MODULE - 2

Principles of Ecology

Ecological Concepts
and Issues

Notes

PRINCIPLES OF ECOLOGY
In the previous module (module-1) you have learnt about the origin and evolution of the
environment. You have also learnt how humans have been interacting with the environment.
In this lesson, which is the first one in the module-2, you will learn some important concepts
of ecology which is an established branch of science.

OBJECTIVES
After completing this lesson, you will be able to:

define the term ecology;

explain the relationship between organism and its habitat with a special mention
of the human species;
recognize the levels of ecological organizations from organism (individual) to
population, community, ecosystem, biome and biosphere;
differentiate between habitat and niche;
describe the concept of species and explain the basic idea of adaptation, evolution
and extinction;
explain the concept of population with reference to organisms;
highlight the characteristics of size, growth, density and dispersion of population;
analyze the demographic factors influencing the changes in population of
organisms;
explain community structure with reference to species diversity, interspecific
interactions and ecological succession.

4.1 DEFINITION OF ECOLOGY

Ecology may be defined as the scientific study of the relationship of living
organisms with each other and with their environment.

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The term ecology was first coined in 1869 by the German biologist Ernst Haeckel. It has
been derived from two Greek words, oikos, meaning home or estate and logos meaning
study. The emphasis is on relationships between organisms and the components of the
environment namely abiotic (non-living) and biotic (living).

Notes

4.2 LEVELS OF ECOLOGICAL ORGANIZATION

Ecology not only deals with the study of the relationship of individual organisms with their
environment, but also with the study of populations, communities, ecosystems, biomes,
and biosphere as a whole (see Fig. 4.1)
A large community unit, characterized by a major
vegetation type and associated fauna, found in a specific
climatic region is a biome
Biomes refer basically to terrestrial areas. The aquatic
systems like the seas, rivers etc. are also divided into
distinct life zones on basis of salinity.

Study of
Levels of
ecological
organization

Types of
study

1. Organisms
(individual)
basic unit of
study

Study of the form,

physiology, behavior,
distribution and
adaptation of
organism in relation
to environment.

2. Population
A group of organisms
consisting of a number
of different populations
that live in defind area
and interact with each
other.
Study of
interaction between
populations and
intraspecific
relationships.

II. Study of human activities

affecting the earth like global
climate, ozone hole etc.
I. Study of physical and
biological features of a
particular biome.

3. Community
A group of organisms
consisting of a
number of different
species that live in
an area and interact
with each other
Study of structure
and composition
of community and
interspecific
interactions
between members
of community.

4. Ecosystem
A communities of
organisms and their
physical
environment,
interacting as an
ecological unit.
Study of the
community in relation
to the structure of its
ecosystem-nutrients
cycling, climate,
energy flow etc.
studied.

Fig. 4.1: Levels of ecological organization and types of ecological studies

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4.3 HABITAT AND ORGANISM

Habitat is the physical environment in which an organism lives. Each organism has particular
requirements for its survival and lives where the environment provides for those needs.
The environmental requirement of an elephant would be a forest. You would not expect an
elephant in the ocean nor would you expect a whale in the forest? A habitat may support
many different species having similar requirements. For example, a single ocean habitat
may support a whale, a sea-horse, seal, phytoplankton and many other kinds of organisms.
The various species sharing a habitat thus have the same address. Forest, ocean, river
etc. are examples of habitat.

Notes

The features of the habitat can be represented by its structural components namely (1)
space (2) food (3) water (4) and cover or shelter (Fig. 4.2).
Earth has four major habitats-(1) Terrestrial (2) Freshwater (3) Estuarine (Where
rivers meet the ocean) and (4) Ocean. The human gut is the habitat of a tapeworm and the
rotting log a habitat of a fungus.
Food

Space
Water

Shelter or
cover

Fig. 4.2: Structural components of a habitat

4.4 NICHE AND ORGANISM

In nature, many species occupy the same habitat but they perform different functions. The
functional characteristics of a species in its habitat is referred to as niche in that common
habitat. Habitat of a species is like its address (i.e. where it lives) whereas niche can be
thought of as its profession (i.e. activities and responses specific to the species). The
term niche means the sum of all the activities and relationships of a species by
which it uses the resources in its habitat for its survival and reproduction.
A niche is unique for a species while many species share the habitat. No two species in a
habitat can have the same niche. This is because if two species occupy the same niche they
will compete with one another until one is displaced. For example, a large number of
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different species of insects may be pests of the same plant but they can co-exist as they
feed on different parts of the same plant. (Fig. 4.3).
Lacebug

Notes

Shoot
moth
larva

Serpentine
leaf miners

Root-feeding white grub

Fig. 4.3: Different species of insects feeding on different parts of the same plant
Another example is the vegetation of the forest. The forest can support a large number of
plant species as they occupy different niches: the tall trees, the short trees, shrubs, bushes
and grasses are all part of the forest but because of varying heights they differ in their
requirements for sunlight and nutrients and so can survive together (Fig. 4.4)
Blackburnian warbler

Bay-breasted warbler

Byrtle warbler

Fig. 4.4: The three species of warbler birds search for insects as food in the forest
at different levels in the tree and so occupy different niches
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The most important resources in the niches of animals are food and shelter while in case of
plants, they are moisture and nutrients (phosphorous and nitrogen).Fig. 4.5 shows the
niche of human beings.

Ecological Concepts
and Issues

Notes

Ant, insect

Goat
Grass

Fox

Fruit

Hen

Cow
Fish

Lion

Crab

Whale
Oyster snail

Fig. 4.5: The ecological niche of human being

INTEXT QUESTIONS 4.1

1. What does the term ecology mean?
______________________________________________________________
2. Define the term niche.
______________________________________________________________
3. Give one point of difference between habitat and niche.
______________________________________________________________

4.5 ADAPTATION
Every organism is suited to live in its particular habitat. You know that the coconuts cannot
grow in a desert while a camel cannot survive in an ocean. Each organism is adapted to its
particular environment. An adaptation is thus, the appearance or behaviour or
structure or mode of life of an organism that allows it to survive in a particular
environment. Presence of gills and fins are examples of adaptation in fishes to aquatic
habitat. In aquatic flowering plants absence of wood formation and highly reduced root
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Notes

Environmental Science Senior Secondary Course

system are adaptations to aquatic environment. Adaptations that can be observed in structure
(Fig. 4.6) or behaviour or physiology of an organism. Adaptations have genetic basis and
have been produced and perfected through evolution. This means that the adaptions have
developed over many generations to help a species survive successfully in its environment.
Examples of basic adaptations that help animals and plants to survive in their respective
environments.

Shape of birds beak.

The thickness or thinness of fur.

Presence of feathers and wings in birds.

Evergreen and deciduous nature of trees.

Presence and absence of thorns on leaves and stems.

A long thin beak is useful for
pulling worms out of mud

The strong beak of parrot is

useful for curshing nuts
This flat beak helps in feeding on
fish, insects and plants in water

Fig. 4.6: Adaptation in the types of beaks in birds: The beaks of different birds are
adopted for feeding on different kinds of food
What is a Species
A species is defined as; a group of similar populations of organisms whose members are
capable of interbreeding, and to produce fertile offspring (children). A tiger, a lion, a lotus
and a rose are examples of different species. Every species has a scientific name, understood
by people of all over the world. Humans belong to species of Homo sapiens. Only
members of the same species can interbreed to produce fertile offspring. Every species
has its own set of genetic characteristics that makes the species unique and different from
other species.
Variation
However, species are generally composed of a number of distinct populations which freely
interbreed even though they appear to be different in appearance.
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Principles of Ecology
Difference in colour of skin, type of hair; curly or straight, eye colour, blood type among
different ethnic groups represent variation within human species. Similarly, different shape
and size of cows, dogs and cats etc. are examples of variation with in each of these species
(Fig. 4.7). In plants, tall and short pea varieties, various shape and size of brinjals exhibit
variation among these plant species. Variations are produced as a result of chance mutation.
Competition and natural selection determines as to which variation will succeed and survive.
Those variations that enable a species to survive in the struggle for existence are encouraged
and promoted.

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Notes

In plants one can observe wide variation in size and shapes of mangoes, brinjals etc.

Fig 4.7: The populations of these four types of dogs look different but all are
capable of breeding among themselves and capable of producing fertile offspring.
All four belong to same species Canis lupus.
Evolution
A valid theory of evolution was propounded by Charles Darwin and Alfred Wallace in
1859. This theory has been extended in the light of progress in genetics and is known as
Neo-Darwinism. It has the following features:
1. Organisms tend to produce more off springs that can be supported by the environment.
2. Mutation (a change in genetic material that results from an error in replication of
DNA) causes new genes to arise in a population. Further, in a sexually reproducing
population, meiosis and fertilization produce new combination of genes every generation,
which is termed recombination. Thus members of the same species show variation
and are not exactly identical. Variations are heritable.
3. An evolutionary force which Darwin termed natural selection, selects among
variations i.e. genes that help the organism to adopt to its environment. Such genes
are reproduced more in a population due to natural selection.

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4. Those offspring which are suited to their immediate environment have a better chance
of surviving, reaching reproductive age and passing on the suitable adaptations to
their progeny.
5. Evolution thus results in adaptation and diversity of the species.

Notes

Sexual reproduction results in

more offspring than
environment can support

Inherited variation expressed in

phenotypes of offspring
Struggle for survival
Some rabbits with thinner
coats die of exposure

Some weaker rabbits die

of disease

Some rabbits lose out in

competition for food and
die

Some slower rabbits are

caught by predators
Healthiest, strongest,
fastest, best insulated
rabbits survive and
breed

Their genes get represented more in the population. Thus National

selection brings about differential reproduction and results in
adaptation

Fig 4.8: Process of natural selection

4.6 SPECIES FORMATION: SPECIATION

The number of species surviving in the world today is the outcome of two processesspeciation and extinction.
Speciation is the process by which new species are formed and evolution is the mechanism
by which speciation is brought about.
A species comprises of many populations. Often different populations of a species remain
isolated due to some geographic barrier such as mountain, ocean, river, etc. Geographic
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isolation occurs when a physical barrier develops between two populations of a species as
you can see in fig. 4.8. The most common way a population undergoes speciation is by
geographic isolation.

The members of a population of a species live in a particular environment and are

capable of breeding with the member of another population of the same species.

The population then becomes separated into two completely isolated populations by
a barrier which prevents their interbreeding and gene exchange. The isolating mechanism
may be a physical barrier like water, mountain, ocean represent geographical isolation.
(Fig. 4.9)

Ecological Concepts
and Issues

Notes

Large interbreeding population

of one species A

Isolation by barrier
BA
RR
IE
R

Sub-population B

Mutation

Sub-population C

BA
RR
IE
R

Large mutant
Small mutant
Natural selection
BA
RR
IE
R

Large size enjoys selection

Small size enjoys selection
advantage (e.g. in cold climate)
advantage (e.g. in warm climate)
Further natural selectionleads to
formulate of two species
BA
RR
IE
R

Species A
Species B
Barrier removed
Species B cannot
breed with species
C or with original
parent species A

Fig. 4.9: Geographical isolation

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Ecological isolation caused by differences in temperature, humidity, pH etc. in the

environment of the two populations.

Reproductive isolation caused by interference in interbreeding between members of

different populations of species i.e. species. When two populations of a species are
unable to interbreed due to reproductive barrier.

Reproductive isolation may occurs due to any one or more of the following reasons:

Notes

(i) When two different populations become sexually receptive at different times of
the year. For example a population of frogs that breeds in May is effectively isolated
from one that breeds in July, though both populations may occur in the same area.
(ii) Members of different populations are not attracted by courtship behaviour towards
one another.
(iii) Pollination mechanism fails, between flowers of two populations.
(iv) Cross fertilization is prevented as sex organs of different populations of a species
do not match.

Mutations occur randomly in isolated populations giving rise to new variation within
each sub-population of these mutations those that help to adapt to the environment are
reproduced in greater numbers in the next generation due to natural selection.

In other words since no two environments are identical, natural selection pressures
that occur on each separate sub-population are different, depending on local conditions
such as climate, disease, predators etc. Natural selection affects each sub-population
differently and so different variations caused by nutrition or recombination in different
subpopulations get established. With the passage of time, the sub populations become
more and more different from each other.

After a long period of time, the sub-populations become very different and get isolated,
reproductively, i.e. they no longer interbreed.

Later even when the barrier is removed the sub-populations are unable to interbreed
and thus subsequently the sub-populations become two different species.

An example of formation of new species

A current example of speciation can be seen in the two species of squirrels Kaibab squirrels
and Abert squirrels that live on opposite sides of the Grand Canyon. Biologists assume
that the two squirrel populations became separate species when about one million years
ago, the Colorado river changed its course, splitting the original population of squirrels into
two. Since the environment on opposite sides of the canyon is different, different
characteristics were favoured on each side of the canyon, by natural selection. After many
years of separation, the genetic differences between the populations became so large that
the two squirrel populations became two separate species. They look different and can no
longer interbreed (Fig 4.10).
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Notes

Kaibab Squirrel (North Rim)

Sciurus kaibabensis

Aberr Squirrel (South Rim)

Sciurus aberti

Fig. 4.10: The Kaibab squirrel of the north rim and the Abert squirrel of the south
rim had common ancestors
4.6.1 Extinction
Ever since life evolved on earth, new species better suited or adapted to the environment
have appeared and older less successful forms have died or become extinct. Extinction is
generally a natural occurrence. It means the dying out of a variety of or a species. The
primary reason for these extinctions is environmental change or biological competition.
Extinction occurs when species cannot evolve fast enough to cope with the changes taking
place in their environment. (Fig. 4.11). Many species have gone extinct during geological
history of the earth. Fossils are, the preserved remains of animals, plants, and other
organisms that lived in the geological past.

(a)

(b)

Fig. 4.11: (a) Fossil of fern plant. (b) Fossil fish

Extinction may take place due to catastrophic natural phenomena such as tsunami, volcanoes
etc. In recent time, human activities such as deporation, over exploitation, environmental

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pollution and environmental change are other factors responsible for extinction. Deforestation
for expansion of industries and human settlements has promoted economic growth but at
the same time it has resulted in habitat loss for many wild plants and animals. Pollution has
killed many an aquatic species.

Notes

INTEXT QUESTIONS 4.2

1. What is meant by the term adaptation? Answer in one sentence.
______________________________________________________________
2. Define : (i) species (ii) variation
______________________________________________________________
3. Name two sources of variation.
______________________________________________________________
4. Name the evolutionary force which brings about greater reproduction of adaptive
variation.
______________________________________________________________
5. Explain the term (i) speciation and (ii) extinction.
______________________________________________________________

4.7 POPULATION
Population is defined as a group of freely interbreeding individuals of the same species
present in a specific area at a given time. For example, when we say that the population of
a city is 50,000, we mean that there are 50,000 humans in that city. However, all populations
of humans living in any part of the world constitute the species Homo sapiens.
A population has traits of its own which are different from those of the individuals forming
the population. An individual is born and dies but a population continues. It may change in
size depending on birth and death rates of the population. An individual is either female or
male, young or old but a population has a sex ratio and age structure, which means, the
ratio of male to female in the population and the various age groups into which the population
may be divided.
The characteristics of any population depends on:
(i) density of the population, (ii) natality (birth rate), (iii) mortality (death rate), (iv) dispersal,
(v) biotic potential (vi) age distribution (vii) dispersion and (viii) growth form.

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Density: The number of individuals per unit area at a given time is termed as population
density. The density of species varies from time to time and from one place to another.
For example, you may notice more plant and animal species in the garden during the
monsoon season. Density of a particular organism in a region is determined by selecting
random samples of a particular dimension size called quadrat from that region.

Ecological Concepts
and Issues

Notes

In case of large, mobile animals like tigers, leopards, lions, deer etc, the density may be
determined by counting individual animals directly or by the pugmarks (foot imprints) left
by the animals in a defined area (Fig. 4.12). Pugmarks of each individual animals are
unique and different from one others. Study of pug marks can provide the following
information reliably if analyzed skillfully:

Presence of different species in the area of study.

Identification of individual animals.

Population of large cats (tigers, lions etc.).

Sex ratio and age (young or adult) of large cats

Hyaena
Wolf
Lion

Pagmark of a cat

Fig. 4.12: Pugmark of a lion/cat (Foot prints) of soft padded wild animals
Counting of human population is called census and is carried out by the Indian government
every 10 years. In census however each individual is physically counted.

Natality: The rate at which new individuals are born and added to a population
under given environmental conditions is called natality. Birth, hatching, germination
and vegetative propagation cause an increase in the number of individuals in a population.
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In case of humans, natality or birth rate is usually expressed in terms of births per
thousand per year.

Mortality: Loss of individuals from a population due to death under given

environmental conditions is called mortality. The number of individuals dead in a year
is calculated for obtaining the mortality rate or death rate. Mortality rate in human
population may be expressed in terms of number of persons dead per thousand per
year.

Dispersal: The movement of individuals of a population out of a region on a permanent

basis is termed emigration while immigration refers to the movement of individuals into
a new area where dispersal includes both emigration and immigration of individuals.
The population of a region is affected by dispersal. Active migration is not possible in
plants though seeds may be dispersed over long distance by wind, water and animals.

Notes

The density of a population thus basically depends on four factors: i) natality, ii) mortality,
iii) immigration and iv) emigration (Fig. 4.13)
Immigration
(+)
(+)
Natality
(-)

(-)
Density

Mortality

Emigration
Fig. 4.13: Parameters of population
Age distribution
Natural populations include individuals of all age groups. It, therefore, becomes necessary
for us to consider age distribution of a population. Age distribution refers to the proportions
of individuals of different age groups in a population.The population may be broadly divided
into three age groups:

pre-reproductive group: comprising of juvenile individuals or children,

reproductive group: consisting of individuals capable of reproduction ,

post-reproductive group: contains aged individuals who are incapable of reproduction.

A rapidly growing population will usually contain a large proportion of individuals in the
reproductive age group; a stationary population (where there is no increase or decrease in
population) contains an even distribution of all age groups, and a declining population
contains a large proportion of old or post-reproductive age of an individuals.
Sex ratio
Sex ratio is an important aspect of population. It refers to the ratio between female and
male individuals in a population
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4.8 POPULATION GROWTH

The growth, stability or decline in number of individuals in a population is influenced by its
relation with the environment.
Populations have characteristic patterns of growth with time, which is depicted by population
growth curves. Two basic forms of population growth curves can be identified. (i) J
shaped growth curve and the (ii) S shaped or sigmoid growth curve.

Notes

Density independent population growth

A forest fire may reduce a dense or scanty population drastically. Extreme weather conditions
like drought, rains, floods, storms and sudden rise or fall in temperatures all act as density
independent factors as they tend to cause sudden reduction in population numbers. The
population growth that is depicted by a J shaped growth curve is called density independent
growth.
Generally the J shaped growth curve is typical of the species which reproduce rapidly
and which are greatly affected by seasonally fluctuating environmental factors such as light,
temperature and rainfall. In this type of curve, population density increases rapidly in
exponential (geometric) progression (total number doubles at regular intervals of time) like
this:
2
8

2
16

2
32

2
64

2
128

till a peak is reached.

This type of exponential growth occurs in nature when a population has abundant supply
of resources. After reaching a peak there is a sudden crash or decline due to environmental
or other factors. Such type of growth may be exhibited by insect populations which show
explosive growth during the monsoon season and then abruptly disappear at the end of the
season.

INTEXT QUESTIONS 4.3

1. Define population.
______________________________________________________________
2. Name at least three characteristics of population.
______________________________________________________________
3. What are the factors on which density of a population depends?
______________________________________________________________

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4.9 COMMUNITIES AND THEIR CHARACTERISTICS

In ecology the term community, or more appropriately biotic community, refers to the
populations of different kinds of organisms living together and sharing the same habitat.
Notes

4.9.1 Organization of a biotic community

The characteristic pattern of the community is termed as structure of the community and
is determined by:

the roles played by its various populations;

the range of its various populations;

the type of area that is inhabited by the populations of the community;

the diversity of species in the community;

the interactions between various populations of the community inhabiting the area.

Members of a community also actively interact with their environment. In a community

only those plants and animals survive which are adapted to a particular environment. The
climate determines the type of environment, hence, the type of organisms in a community.
For example, it is the climate of the area which determines whether a given area becomes
a desert or a forest.
Communities created by human such as lawns or crop communities are such man made
communication are crop communities are relatively simple and consists of only one species
as opposed to a natural community characterized by a large number of species. Man
made communities are very unstable and require great deal of care and constant
manipulation and maintenance.
4.9.2 Stratification
Stratification of a community refers to the vertical layers of the vegetation. Tropical forests
represent a good example of vertical stratification. In moist tropical rain forests up to five
distinct strata or layers of vegetation can be formed. These include from the forest floor to
the top (Fig. 4.14):
(i) Ground layer of mosses and liverworts
associated with dead leaves and other
substances rich in organic matter.
(i) Herb or grass layer,
}
(ii) Short shrub layer
(iii) Tall shrub layer
(iv) Layer of under storey of short trees,
(v) Layer of canopy of lower tress and
(vi) Over storey or emergent tree layer
formed by tall trees.
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The bottom layer

The lower layer
The middle layer

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Strata
Emergent trees

Animal life mostly

flying organisms
Main habitat of
forest animals

Dense canaopy
of lower trees

Notes

Animals rarely
descend to forest
floor

Understory of
shorter trees

Animal descend to
forest floor for
short period

Tall shrubs
Low shrubs

Soil fauna

Seedlings
scattered herbs
and a carpet of
rotting vegetation

Fig. 4.14: Stratification in a biotic community

As you can see in the fig. 4.14 the tropical forest the canopy dominates the area. They
modify the light and moisture conditions for the shorter trees growing under them, which in
turn determine the conditions for the ground vegetation. The vertical stratification of the
plant community determines the structure of the community. The vegetation provides a
number of habitats for the various organisms. Different layers of the community are occupied
by different species of plants and animals. Plants and animals of each layer differ in size,
behaviour and adaptation from those of other layers. The different layers of organisms
minimize competition and conflict among the members of the community. The various
species in the community compete with each other for nutrients, space, light and other
resources. (refer again to Fig 4.4). Stratification is a practical strategy to minimize interspecific
competition.
Community Characteristics
Species diversity
An important attribute of a community is its species diversity.
The different kinds of organisms present in a community represent its species diversity.
The species composition or diversity differs from one community to another. Even in the
same community, there may be seasonal variation in species composition.
Species diversity also influences the stability of the community. A stable community is one
which is able to return to its original condition after being disturbed in some way. Communities
with high species diversity have been found to be comparatively more stable.

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The diversity is calculated both by the number of species (richness) and the relative
abundance of each species (evenness). Relative abundance is measure of relative proportion
of different species occurring in a community. The greater the number of species and more
even their distribution the greater is the species diversity.

Notes

4.10 ECOLOGICAL SUCCESSION

Biotic communities are dynamic in nature and change over a period of time. The process
by which communities of plant and animal species in an area are replaced or changed into
another over a period of time is known as ecological succession. Both the biotic and
abiotic components are involved in this change. This change is brought about both by the
activities of the communities as well as by the physical environment in that particular area.
The physical environment often influences the nature, direction, rate and optimal limit of
changes. During succession both the plant and animal communities undergo change. There
are two types of successions (i) Primary succession and (ii) Secondary succession.
4.10.1 Primary succession
Primary succession takes place an over a bare or unoccupied areas such as rocks outcrop,
newly formed deltas and sand dunes, emerging volcano islands and lava flows as well as
glacial moraines (muddy area exposed by a retreating glacier). where no community has
existed previously. The plants that invade first bare land, where soil is initially absent are
called pioneer species. The assemblage of pioneer plants is collectively called pioneer
community. A pioneer species generally show high growth rate but short life span (Fig
4.15)

Bare rock

Lichens

Small annual
Perennial
plants,
herbs, grasses
lichens

Pioneer Stages

Grasses, shrubs,
shade-intolerant trees

Intermediate stages

Shade-tolerant trees

Climax community

Fig 4.15: The orderly sequence of primary succession

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Primary succession is much more difficult to observe than secondary succession because
there are relatively very few places on earth that do not already have communities of
organisms. Furthermore, primary succession takes a very long time as compared to
secondary succession as the soil is to be formed during primary succession while secondary
succession starts in an area where soil is already present.

Ecological Concepts
and Issues

Notes

The community that initially inhabits a bare area is called pioneer community. The pioneer
community after some time gets replaced by another community with different species
combination. This second community gets replaced by a third community. This process
continues sequence-wise in which a community replaced previous by another community.
Each transitional (temporary) community that is formed and replaced during succession is
called a stage in succession or a seral community (Fig. 4.16). The terminal (final) stage of
succession forms the community which is called as climax community. A climax community
is stable, mature, more complex and long lasting. The entire sequence of communities in a
given area, succeeding each other, during the course of succession is termed sere
(Fig 4.16).
The animals of such a community also exhibit succession which to a great extent is determined
by plant succession. However animals of such successional stages are also influenced by
the types of animals that are able to migrate from neighbouring communities. A climax
community as long as it is undisturbed, remains relatively stable in dynamic equilibrium
with the prevailing climate and habitat factors.
Succession that occurs on land where moisture content is low for e.g. on bare rock is
known as xerarch. Succession that takes place in a water body, like ponds or lake is
called hydrarch.

Annual
weeds

Grasses Shrubs Spruces

and other
perennials

Pines

Plowed
field

12 years
pioneer

220
years

Spruces

Immature oaks

Intermediate Stage

Chestnut

Chestnut

Oak

Oak

Hickory

Black
walnut

Tulip
poplar

Maple

Hickory
Climax Community

200 years (variable)

Fig. 4.16: Secondary succession on land

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4.10.2 Secondary succession
Secondary succession is the development of a community which forms after the existing
natural vegetation that constitutes a community is removed, disturbed or destroyed by a
natural event like hurricane or forest fire or by human related events like tilling or harvesting
land.
A secondary succession is relatively fast as, the soil has the necessary nutrients as well as
a large pool of seeds and other dormant stages of organisms.

INTEXT QUESTIONS 4.4

1.Explain in brief (one to two sentences) the following ecological terms:
(i) Succession._______________________________________________________
(ii) Pioneer species. ___________________________________________________
(iii) Climax community _________________________________________________
(iv) Secondary succession ______________________________________________

4.11 BIOTIC INTERACTION

The biological community of an area or ecosystem is a complex network of interactions.
The interaction that occurs among different individuals of the same species is called
intraspecific interaction while the interaction among individuals of different species in a
community is termed as interspecific interaction.
Interactions between organisms belonging to the same trophic level often involve
competition. Individuals of population may compete for food, space and mates. For
example if a mouse has been eaten by a cat, other cats competing for this resource would
have one less mouse to prey on. The snake another predator of the mice would also have
fewer mice to eat during the night if the cat has succeeded. Direct competition though,
between the cat and snake is not much as they prey at different times. They also eat a
variety of different foods. So competition may be intraspecific as well as interspecific.
Interspecific relationship may be direct and close as between a lion and deer or indirect
and remote as between an elephant and a beetle. This is because interactions between two
species need not be through direct contact. Due to the connected nature of ecosystems,
species may affect each other through intermediaries such as shared resources or common
enemies. Specific terms are applied to interspecific interactions depending upon whether
the interaction is beneficial, harmful or neutral to individuals of the species. The various
possible interactions between two species are given in Table 4.1.

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Table 4.1: Possible biological interactions between two species.
S. No.

Type of interaction

1 Result of

Ecological Concepts
and Issues

Effects of interaction

species 2
I.

NEGATIVE INTERACTIONS

i.

Amensalism

one species is inhibited while the

other species is unaffected

ii.

Predation

Predatorprey relationship: one

species (predator) benefits while
the second species (prey) is
harmed and inhibited.

iii.

Parasitism

Beneficial to one species

(parasite) and harmful to the
other species (host).

iv.

Competition

Adversely affects both species

II.

POSITIVE ASSOCIATIONS

i.

Commensalism

One species (the commensal)

benefits, while the other species
(the host) is neither harmed nor
inhibited

ii.

Mutualism

Interaction is favourable to both

species

III.

NEUTRAL INTERACTIONS

i.

Neutralism

Neither species affects the other

Notes

+ =beneficial; = harmful, 0 =unaffected or neutral

Some types of interactions listed by the effects they have on each partner. O is no
effect, is detrimental and + is beneficial.

4.11.1 Types of Interactions

From the table you can see that in certain types of interspecific associations at least one of
the species is harmed by the other. Such associations are termed as negative, in case
where both the associated species are benefited is a positive association and when the
associated species are neither benefited nor harmed represents a neutral interaction and
include:
1. Amensalism: This is a negative association between two species in which one species
harms or restricts the other species without itself being adversely affected or harmed
by the presence of the other species. Organisms that secrete antibiotics and the species
that get inhibited by the antibiotics are examples of amensalism. For example the
bread mould fungi Pencillium produce penicillin an antibiotic substance which inhibits
the growth of a variety of bacteria. Pencillium benefits apparently by having greater
availability of food when the competition because of the bacteria is removed.
2. Predation: In this type of interaction predator captures, kills and eats an animal of
another species called the prey. The predator naturally benefits from this relationship;

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while the prey is harmed. Predators like leopards, tigers and cheetahs use speed, teeth
and claws to hunt and kill their prey.
3. Parasitism: In this type of interaction, one species is harmed and the other benefits.
Parasitism involves parasite usually a small size organism living in or on another living
species called the host from which the parasite gets its nourishment and often shelter.
The parasite is benefited and the host is harmed. Many organisms like animal, bacteria
and viruses are parasites of plants (Fig. 4.18a) and animals (Fig. 4.18b). Plants like
dodder plant (Cuscuta) (Refer again to fig. 4.18a) and mistletoe (Loranthus ) are
parasites that live on flowering plants. Tap worm, round worm, malarial parasite, many
bacteria, fungi, and viruses are common parasites of humans.

(a)

(i)

Dodder, a parasitic plant is eating up a bush

(ii)
Dodder, a leafless parasitic plant,
growing on the leaf of a grass tree

(b) Ascaris lumbricoides infections. A mass of large round worms from a human infestation.

Fig. 4.17: Parasite-host relationship (a) Plant parasite: Dodder (Cuscuta) plant is
a parasitic weed that obtains moisture and nourishment by attaching to a green,
living plant. (b) Animal parasite: Ascaris or round worms are internal parasites
found in the human intestines
4. Competition: This is an interaction between two populations in which both species
are harmed to some extent. Competition occurs when two populations or species,
both need a vital resource that is in short supply. The vital resource could be food,
water, shelter, nesting site, mates or space. Such competition can be: (i) interspecific
competition-occurring between individuals of two different species occurring in a habitat
and (ii) intraspecific competition-occurs between individuals of same species.
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Intraspecific competition occurs between members of the same species and so it is
very intense.
5. Commensalism: In this relationship one of the species benefits while the other is
neither harmed nor benefited. Some species obtain the benefit of shelter or transport
from another species. For example sucker fish, remora often attaches to a shark by
means of its sucker which is present on the top side of its head. This helps the remora
get protection, a free ride as well as meal from the left over of the sharks meal (Fig.
4.18). The shark does not however get any benefit nor is it adversely affected by this
association. Another example of commensalisms is the relationship between trees and
epiphytic plants. Epiphytes live on the surface of other plants like ferns, mosses and
orchids and use the surface of trees for support and for obtaining sunlight and moisture.
The tree gets no benefit from this relationship nor are they harmed.

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Notes

Fig. 4.18: Commensalism: A shark with suckerfish

6. Mutualism: This is a close association between two species in which both the species
benefit. For example of protocorporation the sea anemone, a cnidarian gets attached
to the shell of hermit crabs for benefit of transport and obtaining new food while the
anemone provides camouflage and protection by means of its stinging cells to the
hermit crab (Fig. 4.19).

Fig. 4.19: Sea anemone, attached to a shell inhabited by a hermit crab

However, some mutualisms are so intimate that the interacting species can no longer live
without each other as they depend totally on each other to survive. Such close associations
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are called symbiosis. An example of such close mutualistic association is that of termite
and their intestinal flagellates. Termites can eat wood but have no enzymes to digest it.
However, their intestine contains certain flagellate protists (protozoans) that have the
necessary enzymes to digest the cellulose of the wood eaten by termites and convert it into
sugar. The flagellates use some of this sugar for their own metabolism while enough is left
for the termite. Both termite and flagellates cannot survive without each other. Another
familiar example of symbiosis is seen in pollination of flowers where flowering plants are
cross pollinated by the bees which benefit by getting nectar from the plants and both
cannot survive without the other.
7. Neutralism: Neutralism describes the relationship between two species which do
interact but do not affect each other. It is to describe interactions where the fitness of
one species has absolutely no effect what so ever on that of other. True neutralism is
extremely unlikely and impossible to prove. When dealing with the complex networks
of interactions presented by ecosystems, one can not assert positively that there is
absolutely no competition between or benefit to either species. Since true neutralism is
rare or non-existent, its usage is often extended to situations where interaction are
merely insignificant or neglible.

INTEXT QUESTIONS 4.5

1. Define (a) ecological succession, (b) symbiosis
______________________________________________________________
2. What type of competition exists between members of a deer herd in an area?
______________________________________________________________
3. What type of relationship is represented by a garden spider feeding on a grasshopper?
______________________________________________________________
4. What type of relationship is represented by a flower being pollinated by a butterfly?
______________________________________________________________
5. Which term best fits the relationship of a person who has a lice feeding on his scalp?
______________________________________________________________
6. Which term means two species live together with each providing a benefit to the other
through the relationship?
______________________________________________________________

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Ecological Concepts
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WHAT YOU HAVE LEARNT

Ecology may be defined as the scientific study of the relationships between each other
and with their environment. The term ecology was coined by Ernst Harckel in 1869 .

Ecology encompasses study of individual, organisms, population, community,

ecosystem, biome and biosphere which form the various levels of ecological organization.

Habitat is the physical environment in which an organism lives (it corresponds to address
of an organism).

Niche refers to the functional position of a species in its habitat.

Species is a group of populations whose individual members are capable of interbreeding

with each other to produce a fertile offspring.

Evolution is the change which gives rise to new species. Mutation and recombination
are sources of variation or differences in the genetic make up or gene pool of a
species. Natural Selection is the mechanism proposed by Darwin and Wallace which
interacts with variation to cause greater reproduction of these genes which help in
adaptive to the environment.

Thus Evolution results in adaptation.

Evolution leads to speciation or formation of new species. Isolation is the factor which
supports specimen. Isolation is of two major types (i) geographical isolation (ii)
reproductive isolation.

Many species, however, have been lost forever and not a single individual belonging
to these species which once existed are now present. Extinction may occur due to
catastrophic events in nature or due to human activities.

Population is a group of interbreeding individuals found in a specific time in a particular

geographical area. The characteristics of a population become evident through the (i)
population density (ii) birth rate or natality (iii) death rate or mortality (iv) dispersion
(immigration and migration) (v) age distribution (vi) sex ratio.

Ecological succession is the successive growth of primary succession occurs in an

area where there is no previous community. Secondary succession forms on existing
natural vegetation.

Biotic interaction refers to the interaction taking place between individuals belonging
to the same species (intra specific) or different species (interspecific). Examples are (i)
competition (ii) predation (iii) parasitism (iv) mutualism (v) symbiosis (vi) commensalism
(vii) neutralism

Notes

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Ecological Concepts
and Issues

TERMINAL EXERCISE
1. Define the terms : Ecology, niche, species, extinction.
Notes

2. What do you understand by Variation and Natural Selection? In what way do they
interact to cause evolution?
3. What is the role of isolation in the formation of new species and keeping them distinct.
4. In what ways have humans caused the extinction of species?
5. What do you understand by (i) natality (ii) speciation (iii) mutation (iv) extinction
6. Explain ecological succession.
7. State and explain community characteristics.
8. What are (i) climax community and (ii) pioneer species?
9. Write an essay on biotic interaction.
10. Define biotic Interaction. Describe any one type of positive, negative and neutral
quotation.

ANSWER TO INTEXT QUESTIONS

4.1
1. Ecology means the scientific study of the relationship of living organisms with each
other and with their environment.
2. The term niche means the sum of all activities and relationship a species has while
obtaining and using the resources it needs to survives and reproduce.
3. Habitat is the physical environment where an organism lives while niche is the sum of
all activities and relationship of a species
4.2
1. The appearance or behaviour or structure or mode of life of an organism that allows it
to survive in particular environment.
2. Species a group of similar populations of organisms whose members are capable of
inter breeding to produce fertile offspring.
Variation- differences in structure due to differences in gene combinations.
3. (i) Gene combination (ii) Mutation

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4. Natural selection

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5. Speciation- is the process by which new species are formed and extinction is dying
out of a variety of or a species.
4.3

Notes

1. A Group of freely interbreeding individuals of the same species present in a specific

area at a given time.
2. i) Density of the population
ii) Natality
iii) Mortality (any other)
3. Mortality, natility, immigration, emigration
4.4
1. (i) Succession is the orderly change of organisms in an environment over time.
(ii) Pioneer species is the name use for the first time assemblage of plants that inhabit
as area undergoing changes during succession. They are the first species in successional
process.
(iii) Climax community is the final stage of succession. It is a relatively stable, long
lasting community.
(iv) Secondary succession is the term used for the orderly series of change s that
begins with the disturbance of an existing community and leads to a climax community
4.5
1. The interacting species can no longer time without each other as they depend totally
on each other to survive.
2. Intraspecific competition
3. Predation as it is preying upon or eating the grasshopper.
4. Mutualism as both are helped by the relationship.
5. Host
6. Mutualism

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Notes

ECOSYSTEM
You know that earth is perhaps the only planet in the solar system that supports life. The
portion of the earth which sustains life is called biosphere. Biosphere is very huge and can
not be studied as a single entity. It is divided into many distinct functional units called
ecosystem. In this lesson you will study about the structure and functions of ecosystem.

OBJECTIVES
After completing this lesson, you will be able to:
explain the concept of ecosystem;
recognize the two major components of ecosystem;
describe ecosystem components by giving example of a pond;.
list a few natural and human modified ecosystems;
explain energy flow through food chain;
differentiate between the various trophic levels- producers, consumers and
decomposers;
construct a food chain and representsterrestrial and aquatic ecosystem;
define food web;
define ecological pyramid, pyramid of number, biomass and energy;
explain ecological efficiency;
explain ecosystem growth or evolution of ecosystem;

explain importance of maintaining balanced ecosystem.

5.1 ECOSYSTEM
In the previous lesson, you learnt that in nature several communities of organisms live
together and interact with each other as well as with their physical environment as an
ecological unit. We call it an ecosystem. The term ecosystem was coined by A.G. Tansley
in 1935. An ecosystem is a functional unit of nature encompassing complex interaction
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between its biotic (living) and abiotic (non-living) components. For example- a pond is a
good example of ecosystem.

Ecological Concepts
and Issues

5.1.1 Components of an ecosystem

Components of ecosystem: They are broadly grouped into:-

Notes

(a) Abiotic and (b) Biotic components

Components of Ecosystem
Abiotic components
Physical factors
Temperature
Humidity
Light
Atmospheric pressure

Biotic components

Inorganic substances
Water
Oxygen
Carbon dioxide
Nitrogen
Producers
(Green plants)

Organic substances
Proteins
Carbohydrates
Lipids

Consumers
(Animals)

Decomposers
(Microorganisms)

(a) Abiotic components (Nonliving): The abiotic component can be grouped into
following three categories:(i) Physical factors: Sun light, temperature, rainfall, humidity and pressure. They sustain
and limit the growth of organisms in an ecosystem.
(ii) Inorganic substances: Carbon dioxide, nitrogen, oxygen, phosphorus, sulphur, water,
rock, soil and other minerals.
(iii) Organic compounds: Carbohydrates, proteins, lipids and humic substances. They
are the building blocks of living systems and therefore, make a link between the biotic
and abiotic components.
(b) Biotic components (Living)
(i) Producers: The green plants manufacture food for the entire ecosystem through the
process of photosynthesis. Green plants are called autotrophs, as they absorb water
and nutrients from the soil, carbon dioxide from the air, and capture solar energy for
this process.
(ii) Consumers: They are called heterotrophs and they consume food synthesized by the
autotrophs. Based on food preferences they can be grouped into three broad
categories. Herbivores (e.g. cow, deer and rabbit etc.) feed directly on plants,
carnivores are animals which eat other animals (eg. lion, cat, dog etc.) and omnivores
organisms feeding upon both plants and animals e.g. human, pigs and sparrow.
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(iii) Decomposers: Also called saprotrophs. These are mostly bacteria and fungi that
feed on dead decomposed and the dead organic matter of plants and animals by
secreting enzymes outside their body on the decaying matter. They play a very important
role in recycling of nutrients. They are also called detrivores or detritus feeders.
5.1.2 Functions of ecosystem
Ecosystems are complex dynamic system. They perform certain functions. These are:(i) Energy flow through food chain
(ii) Nutrient cycling (biogeochemical cycles)
(iii) Ecological succession or ecosystem development
(iv) Homeostasis (or cybernetic) or feedback control mechanisms
Ponds, lakes, meadows, marshlands, grasslands, deserts and forests are examples of
natural ecosystem. Many of you have seen an aquarium; a garden or a lawn etc. in your
neighbourhood. These are man made ecosystem.
5.1.3 Types of ecosystems
Ecosystems are classified as follows:
(i) Natural ecosystems (ii) Man made ecosystems
(i) Natural ecosystems
(a) Totally dependent on solar radiation e.g. forests, grasslands, oceans, lakes, rivers and
deserts. They provide food, fuel, fodder and medicines.
(b) Ecosystems dependent on solar radiation and energy subsidies (alternative sources)
such as wind, rain and tides. e.g tropical rain forests, tidal estuaries and coral reefs.
(ii) Man made ecosystems
(a) Dependent on solar energy-e.g. Agricultural fields and aquaculture ponds.
(b) Dependent on fossil fuel e.g. urban and industrial ecosystems.
You will study the details of natural and human made ecosystems in lesson 6 and lesson 7
respectively.

INTEXT QUESTIONS 5.1

1. List the abiotic components of ecosystem.
______________________________________________________________
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2. List the biotic components of ecosystem.

Ecological Concepts
and Issues

______________________________________________________________
3. What role do decomposers play in an ecosystem?
______________________________________________________________
4. Mention two examples of (i) natural ecosystem (ii) man made ecosystem.

Notes

______________________________________________________________

5.2 POND AS AN EXAMPLE OF AN ECOSYSTEM

A pond is an example of a complete, closed and an independent ecosystem. It is convenient
to study its basic structure and functions. It works on solar energy and maintains its biotic
community in equilibrium. If you collect a glass full of pond water or a scoop full of pond
bottom mud, it consists of a mixture of plants, animals, inorganic and organic materials.
Following components are found in a pond ecosystem.

Basic inorganic and

organic compounds
Bacteria and fungi
(Reducers)

Fig. 5.1: Pond ecosystem

(a) Abiotic components
(i) Light: Solar radiation provides energy that controls the entire system. Penetration of
light depends on transparency of water, amount of dissolved or suspended particles in
water and the number of plankton. On the basis of extent of penetration of light a pond
can be divided into euphotic (eu=true,photic=light), mesophotic and aphotic zones.
Plenty of light is available to plants and animals in euphotic zone. No light is available
in the aphotic zone.

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(ii) Inorganic substances: These are water, carbon, nitrogen, phosphorus, calcium and
a few other elements like sulphur depending on the location of the pond. The inorganic
substances like O2 and CO2 are in dissolved state in water. All plants and animals
depend on water for their food and exchange of gases- nitrogen, phosphorus, sulphur
and other inorganic salts are held in reserve in bottom sediment and inside the living
organisms. A very small fraction may be in the dissolved state.
(iii) Organic compounds: The commonly found organic matter in the pond are amino
acids and humic acids and the breakdown products of dead animals and plants. They
are partly dissolved in water and partly suspended in water.
(b) Biotic components
(i) Producers or autotrophs: synthesize food for all the heterotrophs of the pond. They
can be categorized into two groups:(a) Floating microorganisms and plants
(b) Rooted plants
(a) Floating microorganisms (green) and plants are called phytoplankton (phyto- plants,
plankton floating). They are microscopic organisms. Sometimes they are so abundant
in pond that they make it look green in colour e.g. Spirogyra, Ulothrix, Cladophora,
Diatoms, Volvox.
(b) Rooted plants: These are arranged in concentric zones from periphery to the deeper
layers. Three distinct zones of aquatic plants can be seen with increasing deapth of
water in the following order:
i) Zone of emergent vegetation: . eg. Typha, Bulrushes and Sagittaria
ii) Zone of rooted vegetation with floating leaves . eg. Nymphaea
iii) Zone of submergent vegetation: eg. All pond weeds like Hydrilla , Rupia,
musk grass etc.
(ii) Consumers/Heterotrophs are animals which feed directly or indirectly on autotrophs
eg. Tadpole, snails, sunfish, bass etc.
Pond animals can be classified into the following groups
(a) Zooplanktons are floating animals. Cyclops, Cypris
(b) Nektons are the animals that can swim and navigate at will. Eg. fishes
(c) Benthic animals are the bottom dwellers: beetle, mites, mollusks and
some crustaceans.
(iii) Decomposers: They are distributed through out the entire in the whole pond but in
the sediment most abundant. There are bacteria and fungi. (Rhizopus, Penicillium,
Curvularia ,Cladosporium) found at the bottom of the pond.

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INTEXT QUESTIONS 5.2

1. What are phytoplanktons?
______________________________________________________________

Notes

2. Where will you search for the decomposers in a pond?

______________________________________________________________
3. How do nektons differ from zooplanktons?
______________________________________________________________
4. From where do the fishes living at bottom of the pond get their food?
______________________________________________________________

5.3 ECOSYSTEM FUNCTIONENERGY FLOW

THROUGH ECOSYSTEM
Food chains and energy flow are the functional properties of ecosystems which make
them dynamic. The biotic and abiotic components of an ecosystem are linked through
them.
5.3.1 Food Chain
Transfer of food energy from green plants (producers) through a series of organisms with
repeated eating and being eaten is called a food chain. e.g.
Grasses Grasshopper Frog Snake Hawk/Eagle
Each step in the food chain is called trophic level. In the above example grasses are 1st,
and eagle represents the 5th trophic level.
Some more example of food chain are given in fig. 5.2.
During this process of transfer of energy some energy is lost into the system as heat energy
and is not available to the next trophic level. Therefore, the number of steps are limited in
a chain to 4 or 5. Following trophic levels can be identified in a food chain.
(1) Autotrophs: They are the producers of food for all other organisms of the ecosystem.
They are largely green plants and convert inorganic material in the presence of solar
energy by the process of photosynthesis into the chemical energy (food). The total
rate at which the radiant energy is stored by the process of photosynthesis in the green
plants is called Gross Primary Production (GPP). This is also known as total
photosynthesis or total assimilation. From the gross primary productivity a part is
utilized by the plants for its own metabolism. The remaining amount is stored by the
plant as Net Primary Production (NPP) which is available to consumers.

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Notes

P = Producer, H = Herbivore, C = Carnivore, C1 = First level carnivore, C2 = Top Carnivore

Fig. 5.2: Some examples of food chain

(2) Herbivores: The animals which eat the plants directly are called primary consumers
or herbivores e.g. insects, birds, rodents and ruminants.
(3) Carnivores: They are secondary consumers if they feed on herbivores and tertiary
consumers if they use carnivores as their food. e.g. frog, dog, cat and tiger.
(4) Omnivores: Animals that eat both plant and animals e.g. pig, bear and man
(5) Decomposers: They take care of the dead remains of organisms at each trophic level
and help in recycling of the nutrients e.g. bacteria and fungi.
There are two types of food chains:
(i) Grazing food chains: which starts from the green plants that make food for herbivores
and herbivores in turn for the carnivores.
(ii) Detritus food chains: start from the dead organic matter to the detrivore organisms
which in turn make food for protozoan to carnivores etc.
In an ecosystem the two chains are interconnected and make y-shaped food chain. These
two types of food chains are:(i) Producers Herbivores Carnivores
(ii) Producers Detritus Feeders Carnivores
5.3.2 Food web
Trophic levels in an ecosystem are not linear rather they are interconnected and make a
food web. Thus food web is a network interconnected food chains existing in an ecosystem.
One animal may be a member of several different food chains. Food webs are more
realistic models of energy flow through an ecosystem (Fig. 5.3).

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Notes

Fig. 5.3: Simple food web

NU

The flow of energy in an ecosystem is always linear or one way. The quantity of energy
flowing through the successive trophic levels decreases as shown by the reduced sizes of
boxes in fig. 5.4. At every step in a food chain or web the energy received by the organism
is used to sustain itself and the left over is passed on to the next trophic level.
NU

NU

Sun light
Autotroph

Light reflected

10,000 kcal

Herbivores
R

1000 kcal

NU = Not utilized

NU
Primary
carnivores

NU
Secondary
Carnivores

100 kcal

10 kcal

NU
Decomposers
Decomposers

R
R

R = Respiration

Fig. 5.4: Model of energy flow through an ecosystem. Boxes indicate the standing
crop biomass and pipes indicate the energy flowing. (NU = Not utilized, R =
Respiration)
5.3.3 Ecological pyramid
Ecological pyramids are the graphic representations of trophic levels in an ecosystem.
They are pyramidal in shape and they are of three types: The producers make the base of
the pyramid and the subsequent tiers of the pyramid represent herbivore, carnivore and
top carnivore levels.
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Environmental Science Senior Secondary Course

(1) Pyramid of number: This represents the number of organisms at each trophic level.
For example in a grassland the number of grasses is more than the number of herbivores
that feed on them and the number of herbivores is more than the number of carnivores.
In some instances the pyramid of number may be inverted, i.e herbivores are more
than primary producers as you may observe that many caterpillars and insects feed on
a single tree. (see fig. 5.5a)
(2) Pyramid of biomass: This represents the total standing crop biomass at each trophic
level. Standing crop biomass is the amount of the living matter at any given time. It is
expressed as gm/unit area or kilo cal/unit area. In most of the terrestrial ecosystems
the pyramid of biomass is upright. However, in case of aquatic ecosystems the pyramid
of biomass may be inverted e.g. in a pond phytoplankton are the main producers, they
have very short life cycles and a rapid turn over rate (i.e. they are rapidly replaced by
new plants). Therefore, their total biomass at any given time is less than the biomass of
herbivores supported by them. (see fig. 5.5b)
(3) Pyramid of energy: This pyramid represents the total amount of energy at each
trophic level. Energy is expressed in terms of rate such as kcal/unit area /unit time or
cal/unit area/unit time.eg. in a lake autotroph energy is 20810 kcal/m/year (see fig.
5.5c). Energy pyramids are never inverted.

Pyramid of Number
Grassland

Pyramid of biomass
grassland

Pyramids of energy
forest

Fig. 5.5: Ecological pyramids

Note : P = Producer; C1= herbivore; C1= Carnivore ; C2= Top carnivore

INTEXT QUESTIONS 5.3

1. Draw a simple food chain.
______________________________________________________________
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2. What is a food web?

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______________________________________________________________
3. Give examples of an inverted pyramids
______________________________________________________________
4. Which type of pyramid gives the true picture of trophic structure of an ecosystem?

Notes

______________________________________________________________

5.4 ECOLOGICAL EFFICIENCY

It is clear from the trophic structure of an ecosystem that the amount of energy decreases
at each subsequent trophic level. This is due to two reasons:
1. At each trophic a part of the available energy is lost in respiration or used up in
metabolism.
2. A part of energy is lost at each transformation, i.e. when it moves from lower to higer
trophic level as heat.
It is the ratio between the amount of energy acquired from the lower trophic level and the
amount of energy transferred from higher trophic level is called ecological efficiency.
Lindman in 1942 defined these ecological efficiencies for the 1st time and proposed 10%
rule e.g. if autotrophs produce 100 cal, herbivores will be able to store 10 cal. and carnivores
1cal. However, there may be slight variations in different ecosystems and ecological
efficiencies may range from 5 to 35%. Ecological efficiency (also called Lindmans
efficiency) can be represented as
I t 100
Ingestion at trophic level t 100
=
It 1
Ingestion at previous trophic level 1

5.4.1 Significance of studying food chains

1. It helps in understanding the feeding relations and interactions among different organisms
of an ecosystem.
2. It explain the flow of energy and circulation of materials in ecosystems.
3. It help in understanding the concept of biomagnification in ecosystems.

INTEXT QUESTIONS 5.4

1. What is the 10% rule of energy transfer in a food chain?
______________________________________________________________

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2. Give formula of Lindmans efficiency.
______________________________________________________________
3. What is the significance of studying food chains?

Notes

______________________________________________________________

5.5 BIOGEOCHEMICAL CYCLES

In ecosystems flow of energy is linear but that of nutrients is cyclical. This is because
energy flows down hill i.e. it is utilized or lost as heat as it flows forward The nutrients on
the other hand cycle from dead remains of organisms released back into the soil by detrivores
which are absorbed again i.e. nutrient absorbed from soil by the root of green plants are
passed on to herbivores and then carnivores. The nutrients locked in the dead remains of
organisms and released back into the soil by detrivores and decomposers. This recycling
of the nutrients is called biogeochemical or nutrient cycle (Bio = living, geo = rock
chemical = element). There are more than 40 elements required for the various life processes
by plants and animals. The entire earth or biosphere is a closed system i.e. nutrients are
neither imported nor exported from the biosphere.
There are two important components of a biogeochemical cycle
(1) Reservoir pool - atmosphere or rock, which stores large amounts of nutrients.
(2) Cycling pool or compartments of cycle-They are relatively short storages of carbon
in the form of plants and animals.
You shall now learn about the bio-geo chemical cycles carbon, nitrogen and water.
5.5.1 Carbon cycle
The source of all carbon is carbon dioxide present in the atmosphere. It is highly soluble in
water; therefore, oceans also contain large quantities of dissolved carbon dioxide.
The global carbon cycle consists of following steps Photosynthesis
Green plants in the presence of sunlight utilize CO2 in the process of photosynthesis and
convert the inorganic carbon into organic matter (food) and release oxygen. A part of the
food made through photosynthesis is used by plants for their own metabolism and the rest
is stored as their biomass which is available to various herbivores, heterotrophs, including
human beings and microorganisms as food. Annually 4-9 x1013 kg of CO2 is fixed by
green plants of the entire biosphere. Forests acts as reservoirs of CO2 as carbon fixed by
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the trees remain stored in them for long due to their long life cycles. A very large amount of
CO2 is released through forest fires.

Ecological Concepts
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Notes

gas

Fig. 5.6: Carbon cycle

Respiration
Respiration is carried out by all living organisms. It is a metabolic process where food is
oxidized to liberate energy, CO2 and water. The energy released from respiration is used
for carrying out life processes by living organism (plants, animals, decomposers etc.).
Thus CO2 is released into of the atmosphere through this process.
Decomposition
All the food assimilated by animals or synthesized by plant is not metabolized by them
completely. A major part is retained by them as their own biomass which becomes available
to decomposers on their death. The dead organic matter is decomposed by microorganisms
and CO2 is released into the atmosphere by decomposers.
Combustion
Burning of biomass releases carbon dioxide into the atmosphere.
Impact of human activities
The global carbon cycle has been increasingly disturbed by human activities particularly
since the beginning of industrial era. Large scale deforestation and ever growing consumption
of fossil fuels by growing numbers of industries, power plants and automobiles are primarily
responsible for increasing emission of carbon dioxide.
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Carbon dioxide has been continuously increasing in the atmosphere due to human activities
such as industrialization, urbanization and increasing use and number of automobiles. This
is leading to increase concentration of CO2 in the atmosphere, which is a major cause of
global warming.
5.5.2 Nitrogen cycle
Nitrogen is an essential component of protein and required by all living organisms including
human beings.
Our atmosphere contains nearly 79% of nitrogen but it can not be used directly by the
majority of living organisms. Broadly like corbondioxide, nitrogen also cycles from gaseous
phase to solid phase then back to gaseous phase through the activity of a wide variety of
organisms. Cycling of nitrogen is vitally important for all living organisms. There are five
main processes which essential for nitrogen cycle are elaborated below.
(a) Nitrogen fixation: This process involves conversion of gaseous nitrogen into
Ammonia, a form in which it can be used by plants. Atmospheric nitrogen can be fixed
by the following three methods:(i) Atmospheric fixation: Lightening, combustion and volcanic activity help in the
fixation of nitrogen.
(ii) Industrial fixation: At high temperature (400oC) and high pressure (200 atm.),
molecular nitrogen is broken into atomic nitrogen which then combines with hydrogen
to form ammonia.
(iii) Bacterial fixation: There are two types of bacteria(i) Symbiotic bacteria e.g. Rhizobium in the root nodules of leguminous plants.
(ii) Freeliving or symbiotic e.g. 1. Nostoc 2. Azobacter 3. Cyanobacteria can
combine atmospheric or dissolved nitrogen with hydrogen to form ammonia.
(b) Nitrification: It is a process by which ammonia is converted into nitrates or nitrites
by Nitrosomonas and Nitrococcus bacteria respectively. Another soil bacteria
Nitrobacter can covert nitrate into nitrite.
(c) Assimilation: In this process nitrogen fixed by plants is converted into organic molecules
such as proteins, DNA, RNA etc. These molecules make the plant and animal tissue.
(d) Ammonification : Living organisms produce nitrogenous waste products such as
urea and uric acid. These waste products as well as dead remains of organisms are
converted back into inorganic ammonia by the bacteria This process is called
ammonification. Ammonifying bacteria help in this process.
(e) Denitrification: Conversion of nitrates back into gaseous nitrogen is called
denitrification. Denitrifying bacteria live deep in soil near the water table as they like to
live in oxygen free medium. Denitrification is reverse of nitrogen fixation.

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Notes

Ammonia

Fig. 5.7: Nitrogen Cycle

5.5.3 Water Cycle
Water is essential for life. No organism can survive without water. Precipitation (rain,
snow, slush dew etc.) is the only source of water on the earth. Water received from the
atmosphere on the earth returns back to the atmosphere as water vapour resulting from
direct evaporation and through evapotranspiration the continuous movement of water in
the biosphere is called water cycle (hydrological cycle). You have already studied that
earth is a watery planet of the solar system, about 2/3rd of earth surface is covered with
water. However a very small fraction of this is available to animals and plants.
Water is not evenly distributed throughout the surface of the earth. Almost 95 % of the
total water on the earth is chemically bound to rocks and does not cycle. Out of the
remaining 5%, nearly 97.3% is in the oceans and 2.1% exists as polar ice caps. Thus only
0.6% is present as fresh water in the form of atmospheric water vapours, ground and soil
water.
The driving forces for water cycle are 1) solar radiation 2) gravity .
Evaporation and precipitation are two main processes involved in water cycle. These two
processes alternate with each other
Water from oceans, lakes, ponds, rivers and streams evaporates by suns heat energy.
Plants also transpire huge amounts of water. Water remains in the vapour state in air and
forms clouds which drift with wind. Clouds meet with the cold air in the mountainous
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regions above the forests and condense to form rain precipitate which comes down due to
gravity.

Notes

Fig. 5.8: Water Cycle

On an average 84% of the water is lost from the surface of the through oceans by
evaporation. While 77% is gained by it from precipitation. Water run off from lands through
rivers to oceans makes up 7% which balances the evaporation deficit of the ocean. On
land, evaporation is 16% and precipitation is 23%.

5.7 HOMEOSTASIS OF ECOSYSTEM

Ecosystems are capable of maintaining their state of equilibrium. They can regulate their
own species structure and functional processes. This capacity of ecosystem of self regulation
is known as homeostasis. In ecology the term applies to the tendency for a biological
systems to resist changes. For example, in a pond ecosystem if the population of
zooplankton increased, they would consume large number of the phytoplankton and as a
result soon zooplankton would be short supply of food for them. As the number zooplankton
is reduced because of starvation, phytoplankton population start increasing. After some
time the population size of zooplankton also increases and this process continues at all the
trophic levels of the food chain.
Note that in a homeostatic system, negative feed back mechanism is responsible for
maintaining stability in a ecosystem.
However, homeostatic capacity of ecosystems is not unlimited as well as not everything in
an ecosystem is always well regulated. You will learn about the scope and limitations
homeostatic mechanisms when you gain more knowledge about ecosystems. Humans are
the greatest source of disturbance to ecosystems.
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Large number of phytoplankton

Increase population of zooplankton due to excess food available

Reduction in phytoplankton

Population of zooplanktons decrease

due to starvation

Population of phytoplankton starts increasing due to less consumption

Ecological Concepts
and Issues

Notes

Fig. 5.9: Homeostasis in ecosystem

INTEXT QUESTIONS 5.5

1. What is a sedimentary cycle?
______________________________________________________________
2. Give an example of gaseous cycle.
______________________________________________________________
3. Why do forest acts as reservoir?
______________________________________________________________
4. Name a symbiotic nitrogen fixing bacteria.
______________________________________________________________
5. What is precipitation?
______________________________________________________________

WHAT YOU HAVE LEARNT

An ecosystem is a functionally independent unit of abiotic and biotic components of

the biosphere.

Climatic regime, inorganic substances, organic compounds, producers, macroconsumers

and microconsumers are of structural components of the ecosystem.

Functional processes an ecosystem are energy flow, food chains, nutrient cycles,
ecosystem development and homeostasis.

All the abiotic factors such as light, temperature, pressure, humidity, salinity, topography
and various nutrients limit the growth and distribution of animals and plants.
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All the living organisms of an ecosystem are interdependent through food chains and
food webs. Removal of any single species of the community causes ecological
imbalance.

Source of energy for all the ecosystems is solar radiations which is absorbed by
autotrophs and passed on to the consumers in the form of food (organic substances).
Energy flow is always down hill and unidirectional.

Gross primary productivity (GPP) is the total amount of solar energy captured and
stored in the form of organic substances by the green plants. Net primary productivity
is the amount of organic substances left in the plant after its own metabolism i.e. GPP
= NPP + plant respiration.

Trophic relationships of the organisms in an ecosystem can be represented graphically

in the form of ecological pyramids the base of the pyramid represents the producers
and successive tiers represent subsequent higher levels.

The nutrients move from the nonliving to the living and back to the nonliving component
of the ecosystem in a more or less circular manner. These nutrient cycles are known as
biogeochemical cycles.

The main components of all the biogeochemical cycles are:a) the reservoir pool that contains the major bulk of the nutrients soil or atmosphere.
b) cycling pool which are the living organisms (producers, consumers and
decomposers), soil, water and air in which it stays temporarily.

TERMINAL EXERCISE
1. Define the following terms.
(i) Autotrophs
(ii) Heterotrophs
(iii) Primary carnivores
(iv) Saprotophs
(v) Omnivores
2. Give reasons whether the following statements are true or false.
(i) Food chains are more stable than food webs.
(ii) Pyramids of energy are never inverted where as pyramid of biomass may
be inverted.

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(iii) A detritus food chain begins with autotrophs.

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(iv) Phytoplankton is the term applied to floating organisms in a pond.

(v) Aphotic is the upper zone of a pond.
3. Give reasons for the following statements:

Notes

(i) We see more wall lizards near the tube light during summer.
(ii) Energy pyramids are never inverted.
(iii) We can not directly use atmospheric nitrogen.
(iv) There is higher concentration of cabon dioxide in the aphotic zone.
(v) Food chains have a limited number of steps
4. What is an ecosystem? Explain its structural components.
5. Define decomposers and give their role in sustaining an ecosystem.
6. Why are ecosystems dynamic in nature? Give the various functional components of an
ecosystem.
7. What is an ecological pyramid? Define and differentiate between different pyramid of
energy and pyramid of numbers.
8. List the various steps of nitrogen cycle in a sequence.
9. The following organisms were identified in a pond ecosystem-Spirogyra, Euglena,
Hydra, Daphnia, arthropod larvae, bass and sunfish. Make a food web and identify
the trophic level of each one of them.
ACTIVITIES
1) Visit a pond near your house and make the following observations:
(a) note the colour of water
(b) transparency (tie a white stone to a thread ,insert it into pond and measure
the depth upto which you can see it)
(c) check its pH with litmus paper
(d) count the number of different types of plants in it (looking at the shape of
the leaves)
(e) Take a small amount of pond water in a petri dish and observe it under the
binocular for different phytoplanktons and zooplanktons.
Make sketches of these organisms that you observed.
2) Observe a park in your locality before and after the rains for one month and record
your observations (count the number of different plant, insects, birds and rodents).

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3) Collect a bowl full of mud from an open space near your house during rainy season
and observe different types of worms in it. bernetic or homeostasis

ANSWER TO INTEXT QUESTIONS

Notes

5.1
1. Physical, inorganic and organic substance.
2. Producer, consumer and decomposers.
3. They help in decomposing dead organic material and dead plants and animals therefore
they are important for recycling of nutrients.
4. (i) Pond, lake, forests, ocean (any two)
(ii) Agriculture, aquaculture
5.2
1. Microscopic floating vegetation in an aquatic ecosystem.
2. At the bottom of pond.
3. Zooplanktons are free floating and whereas nektons can aquatic animal can surim and
narrgate.
4. Bentic animals like bettle, mites, mollusks and Crustrceans formed are by these fission.
5.3
1. Grass rat snake eagle forest deer tiger
2. Food web Inter connected food chains of an area form a food web.
3. Pyramid of number in case of a tree or in a pond.
4. Pyramid of energy.
5.4
1. 10% rule is i.e. related to ecological efficiency and states that the amount of energy
transferred at each tropic level is only 10% of the energy of the previous tropic level.
2.

Ingestion at tropic level t

100
Ingestion at previous level

3. Biomagnifications is the concentration of non-degradable pollutants in the successive

tropic level in a food chain.
5.5
1. Sedimentary cycle It is a type of biogeochemical cycle where the main reservoir is
lithosphere.
2. Nitrogen (N2) and carbon
3. Forests trees have long life and therefore the carbon fixed by them cycles very slowly.
4. Rhizobium
5. Condensation of water vapours to form clouds.
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Natural Ecosystem

Ecological Concepts
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Notes

NATURAL ECOSYSTEM
Whenever you travel long distance you come across changing patterns of landscape. As
you move out from your city or village, you see croplands, grasslands, or in some areas a
forests, desert or a mountainous region. These distinct landscapes are differentiated primarily
due to the type of vegetation in these areas. Physical and geographical factors such as
rainfall, temperature, elevation, soil type etc. determine the nature of the vegetation. In this
lesson you will learn about the natural ecosystems with their varied vegetation and associated
wildlife.

OBJECTIVES
After completing this lesson, you will be able to:

list the various natural ecosystems;

describe the various terrestrial ecosystems;

describe the various aquatic ecosystems (fresh water, marine and estuarine);

recognize ecotones, their significance and the edge effect.

list the major Indian ecosystems;

list the threatened ecosystems-mangrove, wetlands, coastal ecosystems and

islands;

explain the need and methods of conservation of natural ecosystems.

6.1 WHAT ARE NATURAL ECOSYSTEMS

A natural ecosystem is an assemblage of plants and animals which functions as a unit and
is capable of maintaining its identity such as forest, grassland, an estuary, human intervention
is an example of a natural ecosystem. A natural ecosystem is totally dependent on solar
energy. There are two main categories of ecosystems.
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(1) Terrestrial ecosystem: Ecosystems found on land e.g. forest, grasslands, deserts,
tundra.
(2) Aquatic ecosystem: Plants and animal community found in water bodies. These can
be further classified into two sub groups.

Notes
(i) Fresh water ecosystems, such as rivers, lakes and ponds.
(ii) Marine ecosystems, such as oceans, estuary.

INTEXT QUESTIONS 6.1

1. What is a natural ecosystem?
______________________________________________________________
2. Which are the main categories of natural ecosystems?
______________________________________________________________
3. Give examples of terrestrial ecosystems.
______________________________________________________________
4. Give examples of fresh water ecosystems.
______________________________________________________________

6.2 TERRESTRIAL ECOSYSTEMS

Terrestrial ecosystems are (a) forests (b) grasslands, (c) deserts and (d) tundra
(a) Forests
Forests are large areas supporting rich growth of trees. Depending on the climate and type
of trees they are generally grouped into:
(i) Tropical rain forests
(ii) Temperate deciduous forests
(iii) Boreal or north coniferous forests
(i) Tropical rain forest

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Distribution: These are found in the high rain fall areas on either side of the equator.
Such forests are found in the western coast of India, scattered in south east Asia, some
parts of Africa and south America.

Flora and fauna: Tropical rainforests occur in areas by having high temperature and
high humidity and receives above 200 cm of rainfall per year. Soil is rich in humus.

Natural Ecosystem
These forests have a very rich biodiversity e.g. Brazilian tropical rain forests have
more than 300 species of trees in an area of 200 square kilometer. Trees are tall
growing upto 50 to 60 m. These forests also support epiphytes, like vines, creepers,
woody creepers and orchid etc. These forests are rich in tree dwelling animals such as
monkeys, flying squirrels, snails, centipedes, millipedes, and many insect species are
common on the forest floor.

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Notes

(ii) Temperate deciduous forests

Distribution: They occur mostly in northwest, central and eastern Europe, eastern
north America, north China, Korea, Japan, far eastern Russia and Australia. Trees of
deciduous forests shed their leaves in autumn and a new foliage grows in spring.

Climate: These forests occur in the areas of moderate climatic conditions such as
temperature ranging but 10 to 20oC with a 6 month long winter and an annual rainfall
between 75 to 150 cm. They have its brown soils which are rich in nutrients.

Flora and fauna: Common trees are oak, beach, heath, chest nut, birch, pine. These
forests also show stratification and have a under storey of saplings shrubs and tall
herbs. Prominent grazers include deer, bison and rodents. Rodents play a very important
role in these forests. They feed on seeds, fruits and tree leaves. Black bear, raccoons,
wild cat, wolves, fox and skunks are the omnivores found in these forests. Hibernation
or winter sleep during winter is a common feature of animals found in these forests.
Invertebrate fauna comprises green flies, aphids, certain moths and butterflies.

(iii) Boreal or north coniferous forests:

Distribution: Coniferous forests are also known as Taiga. They extend as a continuous
belt across north America and north Eurasia below the arctic tundra. There is no
counterpart of these forests in southern hemisphere as there is no land at this latitude.
Climate is cold with long, harsh winter, with mean annual temperature below 00C. The
soils are acidic and poor in nutrients.

Flora and fauna: Coniferous forests are characterized by evergreen, drought resistant
and woody. Conifers (gymnosprerms) e.g. spruce, fir and pine trees which bear naked
seeds in cones. The animals found in these forests, are red squirrel, deer, goat, mule,
moose etc. The carnivores which feed upon them are timber wolves, lynxes, bear.
Some common birds are crossbill, thrushes, warblers, flycatchers, robin and sparrow.

(b) Grasslands

Distribution: Grasslands are areas dominated by grasses. They occupy about 20%
of the land on the earth surface. Grasslands occur in both in tropical and temperate
regions where rainfall is not enough to support the growth of trees. Grasslands are
known by various names in different parts of the world.

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Place

Notes

Name of the grassland

North America

Prairies

Eurasia (Europe and Asia)

Steppes

Africa

Savanna

South America

Pampas

India

Grassland, Savanna

Grasslands are found in areas having well defined hot and dry, warm and rainy seasons.
Tropical grasslands are commonly called Savannas. They occur in eastern Africa, South
America, Australia and India. Savannas form a complex ecosystem with scattered medium
size trees in grass lands.

Flora and fauna: Grasses are the dominating plants with scattered drought resistant
thorny trees in the tropical grasslands. Badgers, fox, ass, zebra, antelope are found
grazing on grasslands support the dairy and leather industries. Grasslands also support
large population of rodents, reptiles and insects.

(c) Deserts

Distribution: Deserts are hot and low rain areas suffering from water shortage and
high wind velocity. They show extremes of temperature. Globally deserts occupy about
1/7th of the earths surface.

Flora and fauna: Cacti, Acacia, Euphorbia and prickly pears are some of the
common desert plants. Desert animals include shrew, fox, wood rats, rabbits, camels
and goat are common mammals in desert. Other prominent desert animals are, reptiles,
and burrowing rodents insects.

Adaptations: Desert plants are hot and dry conditions.

(i) These plants conserve water by following methods:

They are mostly shrubs.

Leaves absent or reduced in size.

Leaves and stem are succulent and water storing.

In some plants even the stem contains chlorophyll for photosynthesis.

Root system well developed spread over large area.

(ii) The animals are physiologically and behaviorally adapted to desert conditions.

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They are fast runners.

They are nocturnal in habit to avoid the suns heat during day time.

Natural Ecosystem

They conserve water by excreting concentrated urine.

Animals and birds usually have long legs to keep the body away from the hot
ground.

Lizards are mostly insectivorous and can live without drinking water for several
days.

Herbivorous animals get sufficient water from the seeds which they eat.

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Notes

Camel is known as the ship of the desert as it can travel long distances without drinking
water for several days.
(d) Tundra
The word tundra means a barren land since they are found in those regions of the world
where environmental conditions are very severe. There are two types of tundra- arctic
and alpine.

Distribution: Arctic tundra extends as a continuous belt below the polar ice cap
and above the tree line in the northern hemisphere. It occupies the northern fringe of
Canada, Alaska, European Russia, Siberia and island group of arctic ocean. On the
south pole Anatarctica tundra in the south pole is very small since most of it is
covered by ocean .
Alpine tundra occurs at high mountains above the tree line. Since mountains are
found at all latitudes therefore alpine tundra shows day and night temperature variations.

Flora and fauna: Typical vegetation of arctic tundra is cotton grass, sedges, dwarf
heath, willows, birches and lichens. Animals of tundra are reindeer, musk ox, arctic
hare, caribous, lemmings and squirrel.

Most of them have long life e.g. Salix arctica that is arctic willow has a life span of 150 to
300 years. They are protected from chill by the presence of thick cuticle and epidermal
hair. Mammals of the tundra region have large body size and small tail and ear to avoid the
loss of heat from the surface. The body is covered with fur for insulation. Insects have
short life cycles which are completed during favourable period of the year.

INTEXT QUESTIONS 6.2

1. What are deciduous trees?
______________________________________________________________
2. Explain two common characteristics of the desert.
______________________________________________________________
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3. How are the animals and plants of deserts adapted to heat and drought?
______________________________________________________________
4. Where are Prairies and Steppes are found?
______________________________________________________________

Notes

6.3 AQUATIC ECOSYSTEMS

Aquatic ecosystems refers to plant and animal communities ocuring in water bodies. Aquatic
ecosystems are classified on the basis of salinity into following two types:
(i) Freshwater
(ii) Marine
(i) Fresh water ecosystem
Water on land which is continuously cycling and has low salt content is known as fresh
water and its study is called limnology.
(i) Static or still water (Lentic) e.g. pond, lake, bogs and swamps.
(ii) Running water (Lotic) e.g. springs, mountain brooks, streams and rivers.
Physical characteristics: Fresh waters have a low concentration of dissolved salts.
The temperature shows diurnal and seasonal variations. In tropical lakes, surface temperature
never goes below 400C, in temperate fresh waters, never goes above or below 40C and in
polar lakes never above 40C.

In temperate regions, the surface layer of water freezes but the organisms survive
below the frozen surface.

Light has a great influence on fresh water ecosystems. A large number of suspended
materials obstruct penetration of light in water.

Certain animals float upto water surface to take up oxygen for respiration Aquatic
plants use carbon dioxide dissolved in water for photosynthesis.

Lakes and ponds are inland depressions containing standing water. The largest lake in
the world is lake Superior in North America. Lake Baikal in Siberia is the deepest.
Chilka lake of Orissa is largest lake in India.

Three main zones can be differentiated in a lake:-

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Peripheral zone (littoral zone) with shallow water.

Open water beyond the littoral zone where water is quite deep.

Bentic zone (bottom) or the floor of the lake.

Natural Ecosystem
Aquatic organisms can be floating in water or free swimming or sedentary (fixed), depending
on their size and habit. Microscopic floating organisms such as algae, diatoms, protozoans
and larval forms are called plankton. Rooted aquatic plants, fish, mollusk and echinoderms
are bottom dwellers. (Recall from lesson-5, Fig. 5.1)
Wetlands are areas that periodically get inundated with water and support a flourishing
community of aquatic organisms including frog and other amphibians. Swamps, marshes
and mangroves are examples of wetlands.

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Notes

(ii) Marine ecosystem: Pertains to the seas and oceans including marine organisms.
Distribution: Marine ecosystem covers nearly 71% of the earths surface with an
average depth of about 4000 m. Fresh water rivers eventually empty into ocean. Different
kinds of organisms live at different depths of the sea or ocean.
Salinity of open sea is 3.6% and is quite constant.
The range of temperature variation is much less in the sea than on the land. Hydrostatic
pressure due to water column increases with depth in oceans. It is
1 atm near the surface and 1000 atm at greatest depth. Animals in the deeper layers are
adapted to the high pressure. Some marine organisms such as sperm whales and certain
seals can dive to the great depths and swim back to the surface without difficulty. Tides,
due to gravitational pull of the moon are a common feature of marine ecosystems.
Flora and fauna: Biodiversity of the marine ecosystems is very high as compared to
terrestrial ecosystems. Almost every major group of animals occurs in the sea. Insects and
vascular plant are completely absent in marine ecosystem. Maximum diversity of marine
organisms is found in the tidal zone that is near the shore. Diatoms, algae, dinoflagellates
and jelly fishes are some of the free floating life forms in oceans. Large crustaceans, molluscs,
turtles and mammals like seals, porpoises, dolphins and whales are free swimming animals
that can navigate. Bottom dwellers are generally sessile (fixed) organisms like sponges,
corals, crabs and starfish.
Adaptations:

Light weight animals and plants float in water and move with the water currents.

Animals and plants in ocean are tolerant to high concentration of salts (osmoregulation).
Osmoregulation is the process by which a constant osmotic pressure is maintained in
blood.

Swimming animals have streamlined body. Their body is laterally compressed.

Deep sea forms show bioluminescence (they emit light).

They are dependent for their food on the upper sea zones.
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and Issues

INTEXT QUESTIONS 6.3

1. What is plankton?
Notes

______________________________________________________________
2. What is aquatic ecosystem?
______________________________________________________________
3. Name two plants and two animals which found in marine ecosystem.
______________________________________________________________

6.4 ECOSYSTEMS OF INDIA

India is a vast country and possess many types of natural ecosystems.
(a) Terrestrial

1. Forests
(i) Tropical rain forests
(ii) Tropical deciduous forests
(iii) Temperate broad leaf forests
(iv) Temperate needle leaf or coniferous forests
(v) Alpine and tundra forests
2. Grasslands
3. Deserts
(i) Thar deserts
(ii) Rann of Kutch
4. Mountains The Himalayas
5. Ghats

(b) Aquatic

1. Fresh water ecosystem

2. Marine ecosystem

6.4.1 Terrestrial ecosystem in India

Forests
Forests in India can be classified in different ways, according to their position, atmosphere,
weather condition etc. Some of the common characteristics of various types of natural
vegetation in India includes:

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tropical rain forests,

tropical deciduous forests,

temperate broad leaf forests.

temperate needle leaf or coniferous forests

alpine and tundra forests, etc.

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Notes

Apart from these, there are also some other types of forests are found in India like tidal
forests, Himalayan vegetation, rain forests of southern India, desert region, etc.
(i) Tropical rain forests
The tropical rain forests are playing an important role in natural vegetation in India. These
types of forests include the tropical evergreen forests and tropical semi-evergreen forests
and they are mostly found in places where there is plenty of rainfall and sunshine throughout
the year. Growth of the trees is usually at its best where rainfall is in surplus of 200 cm, with
a short dry season. Such types of forests are found within rainy slopes of the Western
Ghats, plains of West Bengal and Orissa and north-eastern India. Trees grow very briskly
in these forests and attain heights of about 60 m and above. The number of species in these
forests is too vast and too assorted to utilise each one of them commercially. Ebony,
mahogany and rosewood are the main trees of these forests.
(ii) Tropical deciduous forests
Tropical deciduous forests are also known as deciduous (whether it is moist or dry)forests
because they cast leaves for about six to eight weeks in summer. They are also called the
monsoon forests with all their grandeur and beauty. This is so because they form a natural
cover approximately all over India, especially within regions having 200 and 75 cm of
annual rainfall. Most of the tropical deciduous forests are found in the state of Kerala in
India. Apart from Kerala, these forests can be found in the eastern slopes of Western
Ghats and also in the north eastern parts of the peninsular plateau and in the valleys of the
Himalayas. The tropical deciduous forests are pretty substantial, cost- effective and they
demand a lot of maintenance, as they are less resistant to fire. These forests can be divided
into moist and dry deciduous forests. The moist deciduous forests are most commonly
found on the eastern slopes of the Western Ghats. They are also found in the region of
Chhotanagpur plateau, covering east Madhya Pradesh, south Bihar, and west Orissa,
Shiwaliks in the northern India. Important trees of these forests are teak, sal, and
sandalwood.
(iii) Temperate broad leaf forests
It mainly occur between 1500-2400 m altitudes in western Himalayas. Several species of
Oak (Quercus) are found in these forests. Oak species are ever green in the Himalayan
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region. These species show peak leaf fall during summer but never become leafless. Height
of the trees may be 25-30 m. Trees canopy is dense, herbaceaus layer is least developed
and grasses are generally lacking. The Oak forests are often rich in epiphytic flora.
(iv) Temperate needle leaf or coniferous forests
This type of forests are found in the Himalaya over 1700 to 3000 m altitude. These forests
contain economically valuable gymnospermous trees like pine (Pinus wallichiana) deodar
(Cedrus deodara), Cypress (Cypressus torulosa), Spruce (Picea simthiana) and siver fir
(Abies pindrow). Coniferous forests are taller 30-35 m and possess evergreen canopy of
long needle like leaves. Canopy of these trees always remains green. In many species, it is
cone-shaped.
(v) Alpine and Tundra forests
The alpine and tundra forests is another kind of natural vegetation in India. Vegetation
growing at altitudes above 3600 m is usually known as alpine vegetation and it can be
noticed that with the increment of the altitude, the plants show stunted growth. The trees
like silver fir, pine, juniper and birch belong to this category. The alpine grasslands are
mainly found at higher altitudes in this region. The people belonging to the tribal groups like
Gujjar and Bakarwal make extensive use of this region. The vegetations like lichen and
mosses are also found in high altitudinal regions.
The tidal forests provide another variety of natural vegetation in India. They can be
found along the coasts and rivers and they are enshrouded by mangrove trees that can live
in both fresh and salt water. Sundari is a renowned mangrove tree, mainly found in the tidal
forests and it is after this tree that the name Sundarban has been entitled to the forested
parts of the Ganga-Brahmaputra delta.
The Himalayan vegetation is one of the major kinds of natural vegetation in India. The
thick tropical forests in the eastern region of India have a sharp distinction with the pine
and coniferous woodlands of the western Himalayas. Chir pine (Pinus roxburghii) grows
throughout the northwest Himalayas, with the exception of Kashmir. Chilgoza (pine nut),
oak, maple, ash (Fraxinus xanthoxyloides), etc also grow abundantly in the eastern
Himalayas.
The rain forests of Southern India are contributing hugely to the natural vegetation in
India. The most luxuriant rain forests lie on the southwestern coast, in the state of Kerala.
Here the lagoons are canopied by coconut trees and lead to the longest uninterrupted
stretch of rain forests in the country. The Andaman and Nicobar Islands and the state of
Arunachal Pradesh are some of the other regions with well preserved rain forests in India.
Apart from that, dense sandal, teak and sisoo (Dalbergia sissoo) forests also flourish on
the wet Karnataka plateau.

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The Thar Desert presents a wonderful picture of natural vegetation in India. The trees
in this desert are short and stout, and stunted by the scorching sun. Cacti, reunjha (Acacia
leucophloea), khejra (Prosopis spicigera), kanju (Holoptelia integrifolia), Oak
(Calotropis gigantea) etc are common plants in this region. All the above mentioned
varieties of forests and areas are contributing hugely to the natural vegetation in India (Fig.
6.1).

Ecological Concepts
and Issues

Notes

Fig. 6.1 Natural Vegetation

(2) Grasslands
Grasslands are one of the intermediate stage in ecological succession and cover a part of
the land on all the altitudes and latitudes at which climatic and soil conditions do not allow
the growth of trees. In India, grasslands are found as village grazing grounds (Gauchar)
and extensive low pastures of dry regions of western part of the country an also in Alpine
Himalayas . Perennial grasses are the dominant plant community. In some regions grasslands
also support a variety of other herbaceous plants like sedges, legumes and members of the
sunflower family
Grasslands support a large number of herbivores from minute insects to very large mammals.
Rats, mice, rodents, deer, elephant, dog, buffalo, tiger, lion, ferrets are some common
mammals of grasslands. In the north east India, one horned rhinoceros is amongst the
threatened animal of grassland is this region. A large number of avian fauna makes the
grassland colourful.
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(3) Deserts
The Thar desert in Rajasthan is an extension of the Sahara deserts through Arabian and
Persian deserts. They extend from Punjab, Haryana, Rajasthan to Gujarat state.

Notes

Indian deserts are divided into four main types:

hills,

plains with hills,

marshes and

plains with sand dunes.

The distinct Rann of KutchchBhuj in Gujarat forms a separate zone with in Thar deserts
due to its different climatic conditions. It represents vast saline flats. The region of sand
dunes is most spectacular and covers an area of 100,000 sq. km nearly. It extends into
Pakistan. The dunes are highly sandy and contain 0.120.18 mm size grain, 1.8 to 4.5 %
of clay and 0.41.3% of silt.
Since heat and light intensity are very high and sand dunes are shifting, these deserts can
not support vegetation. There are only some thorn forests and dry open grasslands. Indira
Gandhi canal which carries water through Punjab and Haryana enters into Rajasthan
supports some vegetation. The main crops of desert are bajra, millet, wheat, barley, maize,
jowar, guwar. Medicinal plants found here are mehndi, hak, isabgole and gugal.
Indian deserts support many threatened species of birds and mammals, such as Asiatic
lion, wild ass, bats, scaly ant eater, desert fox, Indian gazzel, four horned antelope , white
browed Bushchat, Great Indian Bustard, Cranes and Sandgrouse. Gulf of Kuchch is
distinguished by the presence of living corals, pearl oyster, sea turtles and a large number
of migratory birds like kingfisher, cranes ibis and herons.
(4) Mountains The Himalayas
Distribution: The Himalaya is a great range of mountains that spreads over a westnorthwest to east- southeast over a distance of about 2500 km covering Afganistan ,
Pakistan, India, Nepal, Bhutan and China. In India, it extends from the Indus trench
below Nangaparbat in the west to Yarlungtsangpo- Brahmputra George below
Namchebarwa peak in east.
The Himalayas lying within India occupy nearly 5,31,250 sq. km area
They cover about 16.6% of Indias total geographical area and are spread partially or
completely over 12 states namely: Jammu and Kashmir, Himachal Pradesh, Uttaranchal,
Sikkim, West Bengal, Arunachal Pradesh, Assam, Nagaland, Manipur, Tripura, Mizoram
and Meghalaya.
Himalayas are geographically divided into:
(i) the Eastern Himalayas or the Assam Himalayas: Out of the above the Eastern Himalaya
has a greater diversity of ecosystems like, forests, grasslands, marshes, swamps,
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lakes streams and rivers Eastern Himalayas consists of nearly 8000 species of the
flowering plants. It has many primitive as well as many endemic plant species. Eastern
Himalayas is known as centre of origin of cultivated plants . Many cereals, fruits and
vegetables are cultivated here. E.g. Orchids, Aster, Accasia, Albizzia, Delbergia
species (timber) and many legumes etc.

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(ii) the Central Himalayas or the Nepal Himalayas

(iii) the Western Himalayas: On the western Himalayas cold deserts of Ladakh support
drought and cold resistant varieties of plants and animals e.g. Yak.
(iv) the North-West Himalayas or the Punjab Himalayas
Eastern Himalayas are one of the of the world and has large no animals because of its
varied ecological conditions e.g. Pangolins elephants macaque languor civet.
(5) Ghats
Western and eastern ghats are also important ecosystems of India
Western ghats also known as Sahyadri extend from Tapti river in north to Kanyakumari
in south covering nearly 1,40,000 sq km parallel to the west coast of peninsular India.
They pass through the states of Gujarat, Maharashtra, Goa, Karnatka, Tamilnadu and
Kerala. These ghats are one of the richest biological resources and form distinct ecological
and biogeographical region of India. Western ghats are one of 25 hot spots of the world.
Hot spots are the regions which show maximum biodiversity, richness of species
and endemic forms. These ecosystems are the threatened due to human interference.
June- September are rainy months. The rainfall may vary from 100 to 500 cm. Soil is
mainly red or black in most of the regions and rich in nutrients. 3500 species of flowering
plants have been recorded from western ghats of which nearly1500 are endemic species.
Nearly 209 species of fresh water fishes occur in these ghats of which 120 are endemic.
Similarly out of 219 species of amphibians found here 106 are endemic.
Eastern ghats extend in north south-west strike in Indian peninnsula covering an area of
about 75000 sq. km They are spread through the states of Orissa, Andhra Pradesh and
Tamilnadu. The eastern ghats do not form a continuous range because the great rivers
Mahanadi,Godavari and Krishna cut across them. They are an assemblage of discontinuous
ranges of hills, plateaus and basins. The climate of these ghats may be semiarid to semihumid
with a rainfall ranging from 60 to 160 cm. The vegetation ranges from evergreen trees to
that of dry savannas. The eastern ghats are affected by the human activity. Conservation of
biodiversity here is a big issue today. Special measures are taken to protect this floristic
zone. United Nations Conference on Environment held in Rio de Janerio in 1992 discussed
the issue of conservation of this region.

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6.4.2 Aquatic ecosystem in India
Freshwater ecosystem

Notes

Freshwater are terrestrial aquatic ecosystems. Lakes, flood ponds, reservoirs and rivers
are its important components. The total freshwater area of India is about 7.6 million
hectare.

Lakes are naturally formed deep water bodies e.g. Sultanpur lake, Batkal lake
(Haryana).

Flood points are the places that undergo periodic flooding as a river channel overflows
with flood water i.e. natural areas constituting shallow and seasonal water bodies.
Bank of large rivers have flood points.

Reservoir is man made areas holding water irrigation and human use. e.g, reservoirs
formed by dams used for irrigation.

Rivers are the flowing water bodies as you have studied in this lesson. For example
river Yamuna, Ganga and Tapti, Krishna, Kawari, Narmada etc.

Marine ecosystem
India has a long coastline of about 8000 km stretching along nine states and two island
chains. At the coast a number of rivers form estuaries at their confluence with the sea.
There are three gulfs - one on the east coast that is gulf of Mannar and two on the west
coast i.e. gulf of Kutchch and gulf of Khambhat.
The continental shelf (extension of land into the sea) is 200 m in depth but variable in width
along the coast. The Indian ocean is the smallest of the three great oceans.
The tides are very important in determining the marine life. Nearly 14 species of sea
grasses and 120 species of sea weeds are found along the coast. Representatives of
almost all the invertebrate and vertebrate groups are found in the marine ecosystem.
Corals are the most abundant and play a very important role. 199 Species of corals are
known from Indian Ocean. They make coral reefs which are home to a large number of
other sedentary species like many molluscs, crustaceans and coelenterates. The biodiversity
in a coral reef is comparable to that of a tropical rain forest. Sea shore provides feeding
and breeding ground to a number of birds also. Sea crows, whales and dolphins are the
mammals that have secondarily invaded the sea .
Marine fisheries constitute a highly productive sector in India It is a source of food and
employment to the coastal population.

INTEXT QUESTIONS 6.4

1. Name the various zones of the Himalayas.
______________________________________________________________
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2. Where are deserts found in India?

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______________________________________________________________
3. Give two differences between western and eastern ghats?
______________________________________________________________

Notes

4. Give two Plants and two animals which found in grassland.

______________________________________________________________
5. Name three gulf which are found in India.
______________________________________________________________

6.5 THE THREATENED ECOSYSTEMS

Some of the natural ecosystems are very sensitive to misuse by humans and to natural
disasters or calamities. About such activities you will be study in lesson 12. Natural disasters
are sudden natural accidents or events that cause a lot of damage to natural ecosystems
and human life. Some of the important natural disasters are like tsunamies, earthquakes,
landslides, volcanic eruptions and cyclones.
6.5.1 Estuaries
An estuary is a place where a river or a stream opens into the sea. It is a partially enclosed
coastal area at the mouth of the river where its fresh water carrying fertile silt and runoff
from the land mixes with the salty sea water. It represents an ecotone between fresh
water and marine ecosystem and shows a variation of salinity due to mixing of sea water
with fresh water.
Estuaries are very dynamic and productive ecosystems since the river flow, tidal range
and sediment distribution is continuously changing in them. Examples of estuaries are river
mouths, coastal bays, tidal marshes, lagoons and deltas.
Deltas are triangular areas bordering the river valley towards the mouth. They are
associated with the land projecting into the sea in the form of protuberances.
Estuaries are richer in nutrients than fresh waters or marine waters therefore; they are
highly productive and support abundant fauna. In general the phytoplanktons of estuaries
are diatoms, dinoflagellates, green algae, blue-green algae. Towards the sea coast of the
estuaries there are large algae and sea grasses. Near the mouth of the rivers and deltas
there are mangrove forests.
The vast mangrove forests act as barriers for the costal habitat to check the wind speed
during cyclones and high velocity landward winds.

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All the plants and animals in the estuaries are subjected to variations in salinity to which
they are adapted (osmoregulation).
Estuaries have been damaged due to urbanization, industrialization and population growth.
Aquaculture activities such as prawn seed harvesting has caused considerable damage.
Further, pollution due to industrial effluents and always remains have caused eutrophication.
6.5.2 Mangroves
Mangroves represent a characteristic littoral (near the sea shore) forest ecosystem. These
forests grow in sheltered low lying coasts, estuaries, mudflats, tidal creeks backwaters
(current less, coastal waters held back on land), marshes and lagoons of tropical and
subtropical regions. They are distributed over the east and west coast and island of Andaman
and Nicobar. Since mangroves are located between the land and sea they represent the
best example of ecotone.
Characteristics of mangrove ecosystem:(1) The mangrove forests include a diverse composition of trees and shrubs.
(2) Plants are well adapted to high salinity(halophytic).
(3) Resistant to tidal effect.
(4) Tolerant to high temperature.
(5) Roots bear pneumatophore ( or aerial roots ), which is an aerating system.
Mangroves are highly productive ecosystems and the trees may vary in height from 8 to
20 m. They protect the shoreline from the effect of cyclones and tsunamies.
Indian mangroves are distributed along the east and the west coasts and Andaman and
Nicobar islands. Mangroves along the east coast are more luxuriant and considerably
diverse due to the presence of nutrient rich deltas formed by the rivers Ganga, Mahanadi,
Godavari, Krishna and Cauvery.
The animal communities are of two types:
1. Permanent fauna mainly bentic are molluscs, crustaceans, polychaetes, insects and
birds like kingfishers.
2. Visiting fauna includes mollusks, echinomerms, crustaceans and birds which come
from adjacent terrestrial ecosystems and rivers . Tree frogs, crocodiles, turtles and
snakes are also found in these forests. They are breeding and spawning ground for
many commercially important fishes. Sunderban mangroves are the only mangroves
where tiger population is found.
Mangroves in India have been reduced to more than 50% during the last forty years. They

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are subjected to both natural as well as anthropogenic threats. Natural calamities such as
cyclones, tsunamies and anthropogenic activities such as construction of houses and markets
causing soil erosion and soil sedimentation has lead to their destruction. For example in
Sunderbans collection of tiger prawn seeds for trade has greatly affected the other animals
found in these forests.

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Notes

6.5.3 Islands
Islands are land masses surrounded by sea water from all sides They may be far away
from the continent (oceanic island )or may be very close to it (continental island). India has
two main island groups: 1) Andaman and Nicobar islands in Bay of Bengal and 2)
Lakshadweep in Arabian sea. These ecosystems are threatened mainly due to habitat
destruction for resources and tourism. Although industrial pollution is much less on these
islands, oil spills in oceans have greatly affected their fauna and flora. Many endemic
species of turtles and birds have been threatened to extinction. The Government is taking
special measures to protect them.

INTEXT QUESTIONS 6.5

1. Name two threatened ecosystems.
(i) _________________________ (ii)_________________________
2. Where are mangrove ecosystem found in India.
______________________________________________________________
3. Why is estuary a more productive ecosystem than ocean or fresh water?
______________________________________________________________
4. What are islands?
______________________________________________________________

6.6 ECOTONE
Ecotone is a zone of junction between two or more diverse ecosystems e.g. the mangrove
forests. They represent an ecotone between marine and terrestrial ecosystem.Some more
examples of ecotone are grassland, estuary and river bank
Characteristics of ecotone:
(1) It may be very narrow or quite wide.
(2) It has the conditions intermediate to the adjacent ecosystems. Hence ecotone is a
zone of tension.

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(3) It is linear as shows progressive increase in species composition of one in coming
community and a simultaneous decrease in species of the other out going adjoining
community.
(4) A well developed ecotones contain some organisms which are entirely different from
that of the adjoining communities.
(5) Sometimes the number of species and the population density of some of the species is
much greater in this zone than either community. This is called edge effect. The
organisms which occur primarily or most abundantly in this zone are known as edge
species. In the terrestrial ecosystems edge effect is especially applicable to birds. For
example the density of song birds is greater in the mixed habitat of the ecotone
between the forest and the desert.

6.7 PROTECTION OF NATURAL ECOSYSTEMS

Natural ecosystems have been misused by the human being as a result of which the
biodiversity and wild life has been threatened. Increasing human population, its increasing
needs and greed are the root causes of destruction of natural ecosystems. Destruction and
loss of any of the natural ecosystem will result in ecological imbalance and the human being
(the destroyer) himself will become an endangered species. Hence natural ecosystems
need protection
Protection of natural ecosystem demands management of human use of the biosphere
resources such that they give maximum benefits to the present human generation while
maintaining its potential to meet the needs of future human generations. Protection of
natural ecosystems to an environmentalist means to protect animals and plants in their
natural habitat in totality and not the protection of any one species . It can be achieved by
the following methods:-

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Humans should reduce their needs.

Introduction of the species from the other parts of the world and the human interference
should be reduced to minimum into natural ecosystems.

Some of the areas should be earmarked as protected or reserve zones. This can be
achieved by making buffer or transitional zones around the protected area. (Buffer
zone and transitional zones are where only a few humans are permitted to enter)

Species in the detrimental habitats should be shifted to their unexploited natural

habitat. Delhi Development Authority along with Delhi University has jointly established
a Yamuna Biodiversity park in Delhi to protect and restore natural biodiversity lost
from the Yamuna river bank. The same natural habitat is created for the plants and
aquatic birds. Within a span of one year after the establishment of wetland the number
of migratory birds has increased remarkably.

Natural Ecosystem

Zones of megadiversity and hot spots of biodiversity should be protected.

Megadiversity zones are those regions of the world which have largest number of
species. 200 global megadiversities have been identified. India is one of the
megadiversity countries. Hot spots are the richest and most threatened reservoirs of
plant and animal life of the earth. They have maximum number of endemic species. 25
terrestrial hot spots have been identified for the conservation of biodiversity. They
occupy 1.4% of the earths surface and 20% of worlds the human population lives in
these areas. Western ghats and Eastern Himalayas are two hot spots of India.

International and national level efforts should be made for conserving natural ecosystems
e.g. Earth Summit held in June 1992 at Rio di Janerio , Brazil, it was resolved to make
efforts to protect and conserve biodiversity.

Sacred forests and sacred lakes are protected by the tribal communities due to the
religious sanctity accorded to these forests. They are most undisturbed by human
activity and are known as pristine forests. Chipko movement to protect the forests
of Mandal villages a good example of local peoples effort to conserve natural
ecosystems.

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Notes

INTEXT QUESTIONS 6.6

1. Define ecotone.
______________________________________________________________
2. Give four examples of ecotone.
______________________________________________________________
3. Define edge species.
______________________________________________________________
4. Why there are more number of species of song birds in Mangrove forests?
______________________________________________________________
5. What is meant protection of natural ecosystem for an environmentalist.
______________________________________________________________

WHAT YOU HAVE LEARNT

Natural ecosystems are formed as a result of interaction of regional climate with the
regional substrate without the interference by man.

Natural ecosystems can be classified into two types: 1) terrestrial and 2) aquatic.

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Notes

Terrestrial ecosystems are forests, grasslands, deserts and tundra.

Aquatic ecosystems are fresh waters bodies such as rever, lake and marine habitat
such as seas and ocean.

Similar altitudinal and latitudinal variations in the climatic conditions result in nearly
identical.

Distribution patterns of natural ecosystems from sea level to high mountain peaks and
equator to poles.

Tundra biome occurs in the region where the environmental conditions are very severe
and there is very little vegetation below the poles and at high mountain peaks

Forests are the regions densely packed with tall trees.

Deserts like tundra form an extreme condition in the sequence of biomes. They occur
in dry barren regions of the earth.

Wetlands are ecotones between terrestrial and aquatic ecosystems like marshes,
swamps and mangroves.

Ecotone is a zone of junction between two adjoining communities e.g. estuaries,

mangroves and grassland.

We the human beings are responsible for the reduction of natural ecosystems. To
protect our own species it is essential for us to protect them. Therefore to prevent the
further destruction people should be educated and the various methods should be
adopted for the protection of natural environment and ecosystem balance.

TERMINAL EXERCISE
1. What do you understand by natural ecosystem ? Give examples.
2. Give differences between the following:
a. Alpine and arctic tundra
b. Savanna and prairie
c. Tropical and temperate forests
3. What do you understand by biodiversity? Explain its significance.
4. Give two desert adaptations of plants and animals.
5. Describe the various types of forest found in India (in brief).
6. Explain various zones of Himalayas.

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7. Write short note on grassland and deserts found in India.

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8. Explain how deforestation has resulted in ecological imbalance.

9. What is an ecotone? Explain its significance for the edge species.
10. Give two methods of protecting natural ecosystems.

Notes

ANSWER TO INTEXT QUESTIONS

6.1
1. Is an assemblage of plants and animals functions as a unit and is capable of maintaining
its identity.
2. Terrestrial and Aquatic.
3. Forest, grasslands, deserts and tundra
4. Rivers, lakes and ponds
6.2
1. The leaves of these trees shed in autumn and new foliage grows in spring
2. Hot and low ration areas, suffering from water shortage (any other).
3. Animals are fast runners, nocturnal habit conserve water by excreting concentrated
urine.
Plants are mostly shrubs, leaves absent or reduced in size leaves and stems are
succulent, root system well developed.
4. North America and Eurasia
6.3
1. Microscopic floating organisms such as diatoms, protozoan and larval forms re called
plankton.
2. Refers to plant and animal communities occurring in water bodies. Flora and
Fauna of marine ecosystem
3. Vascular plants are completely absent. Diatoms, algae, dinoflagellates and jelly fishes
are free floating forms. Large crustaceans mollusks, turtles and mammals like seals,
porpoises, dolphins and whales are free floating animals. Bottom dwellers are generally
sessile (fixed) organisms like sponges, corals, crabs and starfish.

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6.4
1. The Eastern Himalayas, the Central Himalayas, the Western Himalayas and the NorthWest Himalayas.

Notes

2. From Punjab, Haryana, Rajasthan to Gujarat state.

3. Eastern Ghats
Extended in north-south-west strike
in Indian peninsula. Rainfall may vary
from 60-160 m vegetation ranpees
from evergreen trees to that of
dry savannas.

Western Ghats
Extended from Tapti river to
Kanyakumari. Rainfall may vary
from 100 to 500 cm. 3500 species
of flowering plants and has been
recorded.

4. Plants - Sedges, legumes and sunflower (Any two)

Animals - Rat, mice, deer, elephant, dog, tiger (Any two)
5. Gulf of Mannar, gulf of Kutchch and gulf of Khambhat.
6.5
1. Estuaries, mangroves and islands (any two).
2. East and west coast and islands of Andaman and Nicobar.
3. Estuaries are very dynamic and productive ecosystems since the river flow, tidal range
and sediment distribution is continuously changing in them. They are richer in nutrients
than fresh waters or marine waters therefore; they are highly productive and support
abundant fauna.
4. Island is land masses surrounded by sea water from all sides.
6.6
1. Ecotone is a zone of function between two or more diverse ecosystems. e.g.
the mangrove forest.
2. Mangrove, grasslands, estuary and river bank.
3. The organisms which occur primarily or most abundantly in this zone are known as
edge species.
4. Because of their mixed habitat of ecotone between the forest and the desert.
5. Protection of natural ecosystems to an environmentalist means to protect animals and
plants in their natural habitat in totality and not the protection of any one species.

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Notes

HUMAN MODIFIED ECOSYSTEMS

The greed and need of human being has modified and changed the natural ecosystems
greatly. The main reasons for the modification of natural ecosystems are and 1) increasing
human population 2) increasing human needs and 3) changing life styles. In this lesson you
will learn about different types of human modified ecosystems, the modifications brought
about for their optimum utilization.

OBJECTIVES
After completing this lesson, you will be able to:

list the various human modified ecosystems;

describe the overall changes in the environment due to rapid growth of human
population and industrialization in India;

explain formation of agro-ecosystems and impact of agricultural practices on

natural environment;

mention the impact of human practices - plantation of forests;

analyze the effect of construction of dams and diversion of rivers on ecological

balance;

list merits and demerits of fish culture pond;

describe the features of urban areas as human modified ecosystems and explain
the environmental consequences;

relate industrialization with environmental degradation;

suggest methods to minimize human impact on ecosystems.

7.1 HUMAN MODIFIED ECOSYSTEMS

Human modified ecosystems may or may not depend on solar energy e.g. in an industry
energy is provided in the form of fossil fuel or electricity or both.

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Some examples of human modified ecosystems are:
(1) Agro-ecosystems
(2) Plantation forests

Notes

(3) Urban ecosystems

(4) Rural ecosystems
(5) Aquaculture
(6) Industrial areas
(7) Laboratory cultures
7.1.1 Characteristics of human modified ecosystems
(1) Highly simplified.
(2) Species diversity is very low.
(3) Food chains are simple and small.
(4) Depend on human (anthropogenic) support for survival; need for fossil fuel energy,
fertilizers, irrigation etc.
(5) Attract large number of weeds.
(6) More susceptible to epidemic diseases.
(7) Suffer from soil erosion.
(8) Highly unstable.

INTEXT QUESTIONS 7.1

1
2

Name two human modified ecosystems.

______________________________________________________________
Give two characteristics of human modified ecosystems.
______________________________________________________________

7.2 IMPACT OF INCREASING HUMAN POPULATION

AND INDUSTRIALIZATION ON ENVIRONMENT IN
INDIA
Human population is rapidly increasing in India consequently our demand for natural
resources is also increasing. The industrialization in India is also increasing at a rapid pace.
The increasing population and growing industrialization are severely affecting the environment
in various ways: Some important impacts are briefly described below:

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Pollution: Development of Science and Technology is a boon to mankind in fulfilling

growing human needs, but on the other hand they have caused environmental pollution.
Pollution refers to the addition of any substance in the environment that has direct or
indirect adverse effect on humans (Lesson 10). The consequences of pollution are
many. Industrial accidents that have taken away several lives e.g. in Bhopal, accidental
leakage of MIC (methyl isocyanate) gas from Union Carbide Company killed more
than 2000 people within 12 to72 hours. Many people lost their eyesight and suffered
from serious medical complications.

Global warming: Increasing use of fossil fuels is a leading cause of increasing levels
of CO2 and other green house gases in the atmosphere. Atmospheric build up of green
house gases have caused considerable heating of the earth leading to global warming.
Global warming is causing melting of glaciers and rise in the sea level. Rising sea level
poses a serious threat to low lying coastal areas and specially to thickly populated
coastal cities like Mumbai, Chennai and Kolkata etc.

Human health and disease: An increase in the population is leading to increasing

incidences of epidemic diseases such as AIDS (Aquired Immuno Deficiency Syndrome),
Hepatitis, T.B. (tuberculosis), bird flu, swine flu, Syphilis, Gonorrhoea,cancer and
many more diseases These diseases are caused by environmental pollution or over
crowding.

Over exploitation of natural resources: Rapidly growing population results in over

exploitation of resources. Over exploitation and introduction of a new or genetically
modified species reduce the productivity of natural ecosystems. For exampleintroduction of new (genetically modified) high yielding variety or non- native species
in any natural ecosystem reduces the population of native species. Over harvesting of
edible fishes reduces their reproductive rate and their population start reducing in
number and may become completely extinct after some time.

Deforestation, over grazing, intensive cultivation, over irrigation etc. results in the loss
of top soil and fertility of the land. Prolonged degradation of land leads to desertification.

Water bodies: Rivers, lakes, ponds, estuaries and oceans are being increasing abused.
Rivers and other water bodies are being used for disposal of all liquid effluents and all
other kinds of wastes. Today most of the water bodies suffer from growing pollution.
Pollution of river Yamuna is one such example.

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Notes

INTEXT QUESTIONS 7.2

1. Name any gas that contributes global warming.
______________________________________________________________

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2. Write the full form of MIC and AIDS.
______________________________________________________________
3. What causes soil erosion?
______________________________________________________________

Notes

7.3 AGROECOSYSTEMS AND AGRICULTURAL PRACTICES

Agroecosystems are large areas where commercial crops are cultivated. Crop plants are
sown and harvested by humans for economic purposes. They are also known as crop
ecosystems and mostly cultivated as monoculture (growing only one type of crop) on the
entire field or some times growing two or more crop species in the same field at the same
time.
7.3.1 Characteristics of agro-ecosystems
(1) They are highly simplified ecosystems supporting monoculture of a crop species.
(2) Species diversity is lowest
(3) Highly unstable and not self sustaining.
(4) Attract weeds and susceptible to plant diseases.
(5) Soil are poor, deficient in nutrients, require supplement of chemical or fertilizers.
(6) Need artificial irrigation and water management.
(7) Dependent on human care and management.
7.3.2 Economic importance
(i) Agroecosystems fulfill the basic requirementsof food, fruits, edible oil etc.
(ii) Good quality grains can be produced with high yield.
(iii) Provides livelihood to a large number of people .More than 70 % of Indian population
depends on agriculture.
7.3.3 Disadvantages of agro-ecosystem

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Large scale monoculture of agricultural crops results in severe loss of native biodiversity
including genetic diversity of crop plants.

High yielding varieties of crop plants are more susceptible to disease e.g. smut of
sugarcane, maize and sorghum and rust of wheat and bajra are common plants diseases.
To protect crop from pests and diseases requires large scale use of pesticides and
chemicals which pollute the environment.

Deplete ground water in many areas due to well irrigation.

Human Modified Ecosystems

Run off water from agricultural field laden with fertilizers and pesticides pollute river,
lakes and ponds.

7.4 PLANTATION FOREST

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Notes

It is a man made ecosystem consisting of individuals of a particular tree species . Trees

planted on barren land, private land, village panchayat land, roadsides, canal banks, along
with railway line and on land not suitable for agriculture. The aim is to grow fast growing
trees which are commercially valuable.
7.4.1 Characteristics of plantation forests
(1) Plantation forests are generally monoculture, like oil palm plantation, rubber plantation,
coffee plantation.
(2) Plantation forests have trees of approximately same age.
(3) Plantation forests are highly susceptible to pathogens are pests.
(4) Poor in species diversity.
(5) Requires constant human care and management.
(6) Recently plantations of Jatropa curcare have become very popular for obtaining
biodiesel.
7.4.2 Economic importance
(1) Tree plantation are raised for fruits, oil, rubber, coffee, timber, fire wood, pulp wood
for making rayon and paper industries.
(2) Trees are also planted to serve as wind breaks or shelter belts.
(3) Tree plantations are also raised for controlling soil erosion and for increasing soil fertility.
(4) Tree plantation provides job opportunities and generate income.

INTEXT QUESTIONS 7.3

1. Name five types of plantations.
________________________________________________________
2. Which type of trees are preferred for plantation forests?
________________________________________________________
3. List any two common features of agro ecosystem and plantation forests.
________________________________________________________
4. Which plant you would recommend to raise a plantation for obtaining bio diesel?
________________________________________________________
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7.5 URBAN ECOSYSTEMS

Notes

Urban life is the life in a city where many people live close together. Presently there seems
to be an urban revolution as people all over the world are moving into towns and cities. In
year 1800, only 5% of the world population was urban-dwelling (50 million people) and in
1985 it increased to 2 billion. At present 45% of the world population is urban population
and by 2030 there will be more than 60% people living in cities.
7.5.1 Characteristics of urban ecosystems
(1) High population density: The maximum population density is observed in Malta Africa.
It is 1100 persons/sq km. Next ranking is Bangladesh with 888persons/sq. km., Bahrin
759 persons/sq km, Netherland 441 persons/sq km and Japan 328 persons/sq km.
(2) Conjestion, shortage of housing and growth of slum areas.
(3) Urban areas import increasing quantity of energy, food and various other materials
from outside to survive.
(4) Generate large quantities of solid and liquid wastes and air pollutants causing problems
of environmental pollution.
(5) More employment opportunities as well as tough competiton.
(6) Better education facilities.
(7) Better medical facilities and health care is provided.
(8) More and diverse sources of entertainment.
7.5.2 Advantages of urban ecosystems
(1) Economically well developed.
(2) Hub of industrial growth.
(3) Centre of commerce.
(4) Multicultural social environment.
(5) Reduced infantile mortality.
(6) Centres of political activity.
7.5.3 Disadvantages of urban ecosystems
(1) Urban areas consume 75% of the earths resources and produce 75% of the waste.
(2) Urban areas are highly polluted since growing number of vehicles and industries emit
large quantities of pollutants.
(3) Suffer from problem of noise pollution is caused by industries and transport.

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(4) Urban ecosystems suffer from serious shortage of water availability.

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(5) High crime rate,unrest and unemployment .

(6) Increasing population density in cities of the world compels some people to live in
slums e.g. in Mumbai 3 million people live in slums pavement and squalter settlements
which lack basic civic facilities like safe drinking water, waste disposed, health care
etc.

Notes

Urban revolution is taking place more rapidly in developing countries like India. The average
growth rate of population twice as fast as the average growth of population. Currently
rate of increase in the population of city dwellers in developing countries is much faster as
compared to the cities of industrialized countries.

7.6 RURAL ECOSYSTEMS

Rural ecosystems are midway between natural and urban ecosystems since the exploitation
of nature and natural resources by humans is relatively much less. Rural people live relatively
close to nature and follow a simple life style.
7.6.1 Characteristics of rural ecosystems

Many villages belong to a single family.

In rural areas people live in small clusters in thatched, mud houses surrounded by farm
lands. In rural areas people are directly or indirectly dependent on agriculture and
consume locally available resources.

Drinking water is largely obtained from wells, canals, lakes or rivers.

Education, healthcare, drainage, sanitation, hygiene, and transport etc. are inadequate
or lacking.

Rural areas are mostly free from air and noise pollution.

The government policies to reduce the migration of people from villages to cities are to
increase the cost of land in the cities and reduce it in the villages. More employment
opportunities should be created in the villages. Some incentives should be given to the
people working in the villages.

INTEXT QUESTIONS 7.4

1. List any two advantages of rural ecosystems.
______________________________________________________________
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2. Why do people tend to migrate from villages to cities?
______________________________________________________________
3. List any two disadvantages of urban ecosystem.

Notes

______________________________________________________________
4. Why do you like to go to a hill station during vacations?
______________________________________________________________

7.7 AQUACULTUREMERITS AND DEMERITS

Aquaculture is the artificial cultivation of aquatic plants or animals. It is primarily carried
out for cultivating certain commercially important edible species of fresh and marine water
fishes, molluscs, crustaceans and aquatic plants. Generally natural water bodies support a
rich biodiversity, very few species are harvested by man. 20,000 species of fish are known
of which only 22 of them are taken largely by man. Fisheries include the extraction of
food from the sea and the fresh water where as aquaculture is rearing of the aquatic
organisms in artificially made water bodies (Fig. 7.1) e.g. culture of fish like carps, tilapia.

Fig. 7.1: Aqualture

There are two types of aquaculture:
1. Fish farming is cultivation of fish in a controlled environment often a coastal or inland
pond, lake, reservoir or rice field (paddy) and harvesting when they reach the desired
size.
2. Fish ranching is a practice of keeping which fishes in captivity for the first few years
in floating cages in coastal lagoons and releasing them from captivity into water bodies.
Adults are harvested when they return for spawning to the lagoons.(for laying eggs)
e.g. Salmon and Hilsa which migrate to rivers to spawn are cultivated by fish ranching
method.

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7.7.1 Fisheries and aquaculture in India
India has a very long coast line for trapping sea food. Marine resources include Bay of
Bengal, Arabian Sea, Indian Ocean, numerous gulfs, coral reefs, mangroves and brackish
waters like lagoons and Chilka lakes in Orissa. Indias inland waters occupy about 1.6
mha (million hectares). They are in the form of major river systems such as Ganges, Yamuna,
Brahmaputra, Narmada, Mahanadi, Cauvery and Krishna and others. Further, there are
canals, ponds, lakes, and irrigation channels where culture fishery can be practised. The
fresh cultured fishes are mostly various species of carps (Labeo, rohita, Catla catla)
Chinese carp, green carp, mirror carps, cat fish etc.

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Notes

Tilapia, trouts, salmons and some more species of fishes are cultured in net pens. Milk fish
and mullets are cultured in enclosures or bamboo fences. Tilapia is a very favourite fish of
many. It is also known as aquatic chicken. They are also grown through small scale
aquaculture by many poor farmers. This fish can grow well even on a low protein diet , and
resistant to many diseases and parasites It can breed rapidly under captivity.
7.7.2 Merit of aquaculture
(1) Ecological efficiency is high. 2 kg. of grains are required to add 1 kg live weight.
(2) High yield in small volume of water.
(3) Improved qualities of fish obtained by selection and breeding and genetic engineering.
(4) Aquaculture reduces over harvesting of fisheries.
(5) High profit.
7.7.3 Demerit of aquaculture
(1) Large inputs of feed, water and land are required.
(2) Loss of native aquatic biodiversity. As it replaced by monoculture of a commercially
important fish species.
(3) Produces large amounts of fish wastes that pollute water bodies.
(4) Destroys mangrove forests or coastal vegetation.
(5) Aquaculture fishes are very sensitive to pesticide runoff from croplands.
(6) In aquaculture ponds high population density is maintained that makes them highly
vulnerable to diseases leading to total collapse of the crop.
(7) Aquaculture tanks or reservoirs are often get contaminated after a few years.

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INTEXT QUESTIONS 7.5

1. What is the difference between fisheries and aquaculture?
Notes

______________________________________________________________
2. Name any two fresh water fishes that are being grown in pond culture.
______________________________________________________________
3. Name the fish that is commonly known as aquatic chicken.
______________________________________________________________
4. In what way aquacultures affect the mangrove forests?
______________________________________________________________

7.8 DAMS, RESERVOIRS AND DIVERSIONS

A dam is a structure built in order to store river or tidal water. Dams, reservoirs and
diversions capture and store runoff water and release it as needed. They are used for:
(1) controlling or moderating floods,
(2) producing hydroelectric power, and
(3) supply water for irrigation, industry and other uses to rural, suburban and urban areas.
Support recreational activities such as swimming and boating.
7.8.1 Advantages of dams
(1) Water released from dams to generate electricity.
(2) Reduce the use of coal and thereby reduce CO2 emission.
(3) Reduce downstream flooding.
(4) Reduce river silting below the dam.
(5) Supply irrigation water for croplands.
7.8.2 Disadvantages of dams
(1) Permanently submerge large areas of forests and crop lands.
(2) Displace large number of native people.
(3) Increase water pollution on account of reduced water flow.
(4) Reduce nutrients replishment of down stream flood plains.
(5) Disrupt spawning and migration of some fish species.
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(6) High cost.

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(7) Large dams i.e. more than 15 meters high (492 feet) increase the risk of inducing
earthquakes specially in earthquake prone areas.
(8) Change physico-chemical quality of water.

Notes

7.9 INDUSTRIALIZATION AND ENVIRONMENTAL

DEGRADATION
A rapid increase in urbanization is resulting in a simultaneous growth of industrialization.
The industrial processes involve mining, manufacturing, metallurgical processing, welding,
grinding and synthesis of chemicals.Industries which are being made by man to make
better use of the primary raw materials produced under natural environmental conditions
cause environmental degradation in the following manner:
Pollution: All these industries discharge several waste gases and particulate pollutants
into the atmosphere. Some of them are as follows:(i) Gaseous pollutants: Oxides of carbon, nitrogen and sulphur.
(ii) Particulate matter: Fine metal dust, fly ash, soot, cotton dust and radioactive substances.
(iii) Burning of plastics: Emit poly chlorinated biphenyles (PCBs) which are harmfull for
lungs and vision.
(iv) Accidental release of some poisonous gases like phosgene (COCl2) and methyl
isocynate (as it happened in Bhopal) are fatal.
(v) Secondary air pollutants formed from complex reactions between primary pollutants,
such as smog and acid rain, which are harmful all living organisms, buildings and
monuments.
Land use and habitat destruction: The natural ecosystems are modified to fulfill the
increasing needs of growing human population 83 % of the earths surface is affected
(excluding Antarctica)by human .Wild life habitat have been degraded,forests have been
cleared which provide habitat for thousands of large and small animals. Industries and
modern transport networks have not only destroyed the natural habitat of animals but
also create noise and thermal pollution. This is seriously affecting growth and reproduction
of wild species of plants and animals resulting in loss of biodiversity.
Human health: Use of various type of chemicals today have serious health implications.
Incidence of cancer, genetic mutations and damage to nervous, immune and hormonal
systems. New disease such as AIDS, mad cow diseases, bird flu and swine flu have
emerged in fast succession due to growing damage to ecology.
Increased sensitivity to diseases: Cultivated species of plants, fishes and other
domesticated animals have become increasingly sensitive to pest and diseases.
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Genetic resistance: An increased use of insecticides, pesticides and antibiotics has speeded
up directional natural selection and caused genetic resistance in the pathogens.
Effect on native populations: Introduction of new alien species or non-native species
reduces the populations growth of native species.

Notes

Stress due to over harvesting: Overgrazing by livestock results in soil erosion and loss
of productivity. Similarly over harvesting of edible fishes reduces population and may
become completely extinct if the over fishing continues for long.
Effect on nutrient recycling: Use of fertilizers in agricultural fields interferes with the
natural biogeochemical cycles.

7.10 METHODS TO MINIMIZE HUMAN IMPACT ON

NATURAL ECOSYSTEMS
Reduce our needs: We should change our habits, curtail our needs and try to conserve
our resources especially food, fuel and water.
Ecoindustrial revolution: The solution to many of the above problems is ecoindustrial
revolution. It refers to a new resource and efficient production system generating minimum
waste. Ecoindustry or industrial ecology is to make industrial manufacturing processes
more sustainable by redesigning the industrial processes along the pattern of natural
processes.

One way is by recycling or reutilizing most of the industrial waste.

Networking of different industries in complex resource exchange web where the waste
of one industry is used as a raw material by for the other and so on.

Industry should strive for higher efficiency of energy and resource use.

INTEXT QUESTIONS 7.6

1. List any two advantages of dams.
______________________________________________________________
2. Name the harmful gas that is released during burning of plastics.
______________________________________________________________
3. How does the introduction of an alieu species affects the indigenous species?
______________________________________________________________
4. What effect does overgrazing by livestock have on grassland?
______________________________________________________________

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Human Modified Ecosystems

Ecological Concepts
and Issues

WHAT YOU HAVE LEARNT

Human modified ecosystems are man made ecosystem, such a agro ecosystem,
aquaculture ponds, cities etc. for his own benefits. They require inputs of fossil fuel for
their survival.

Growth of population and migration of people from rural areas to cities is the root
cause of increased urbanization.

All human modified ecosystems suffer from loss of biodiversity and are not sustainable
on their own.

Most of the current environmental problems are casused by the uncontrolled growth
of human population and growing urbanization and industrialization.

Over harvesting of any species of plant or animal should be controlled to maintain

ecosystem balance.

Agro ecosystems have created many environmental problems such as soil erosion,
ground water depletion and environmental pollution by fertilizers and pesticides.

Ecoindustrial systems should be encouraged to protect the environment.

Notes

TERMINAL EXERCISE
1. Define human modified ecosystems.
2. Give differences between natural and human modified ecosystems.
3. Why the following conditions lead to stress in a population
a) over crowding

b) over harvesting

c) human intervention

4. Give characteristics of human modified ecosystems

5. Write short notes on the following
i) Human population explosion
ii) Industrial pollution
iii) Human health and disease
6. What are the advantages of tree plantation?
7. List some impacts those are leading to environmental degradation?

ANSWER TO INTEXT QUESTIONS

7.1
1. Agro ecosystem, plantation forest, urban ecosystem, rural ecosystem aquaculture (any
two).
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2. (i) Low species diversity, unsustainable and need inputs of human beings in the form
of energy, fertilizers and irrigation and human care to survive etc., They are highly
susceptible to rapid spread diseases. (any two)
7.2

Notes

1. CO2 , Methane
2. Methyl Isocyanate (MIC),
Acquired Immuno Deficiency Syndrome (AIDS)
3. Overgrazing, poor irrigation, over cultration, deforestation
7.3
1. Acassia, Lucaenas (Subabus) Prosopis, Sesbannia, Caruarin Jatropa, Monnga
and neem (any)
2. Fast growing tree species of economic value are preferred.
3. Refer to text
4. Jatropa curcare
7.4
1. Clean and natural environment is available, people have simple life style.
2. For better employment,health and education opportunities and for better living
amenities.
3. Refer to text
4. Highly congested and highly polluted (high levels of water, air and noise pollution),
shortage of living space leading to slum development. (any two)
7.5
1. Aquaculture is the artificial cultivation of aquatic plants and animals whereas fisheries
refers to capturing of fish and othwer aquatic organisms from seas and other fresh
water bodies.
2. Eel, Tilapia, Rohu, Catla, Cat fish (any two)
3. Tilapia
4. Destroys mangrove forest.
7.6
1. They store water, generate hydro electric power increase provide water for crop
irrigation and other domestic uses, reduce downstream flooding (any two).
2. Poly chlorinated biphenyles (PCB)
3. Reduced population of nature species.
4. It results in soil erosion and future loss of productivity.
5. It aims to make industrial manufacturing process is more sustainable by redesigning
them to mini how nature sustain them.

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Human Societies

Human Impact on
Environment

Notes

HUMAN SOCIETIES
Humans have lived in close contact with the environment ever since they first evolved way
back in time between one million to two million years ago. In the beginning they were
hunters and gatherers as you have already learnt in lesson-3. Gradually, with time, humans
began to lead a settled and well organized life. As humans increased in numbers and
progressed culturally, they began to draw more and more from natural resources so much
so that environmental degradation has become a matter of serious concern nowadays.
In this lesson you shall learn about the settlements of humans in villages and cities, related
characteristics, associated life styles and environmental changes resulting from explosive
growth of human population and human settlements.

OBJECTIVES
After completing this lesson, you will be able to:

define urban settlement and differentiate between rural society and urban society;

explain the push and pull factors leading to migration of rural population to cities;

define rural settlements and list the characteristics of rural settlements;

list the special problems of the rural population pertaining to land availability
and land use;

list the effect of modern technology on agriculture and its impact on rural life;

describe the significant features of urban life including facilities as well as its
difficulties specially in the Indian context;

list the special problems of urban areas, changes in life style, land availability;

list the special problems of urban areas like resource consumption and waste generation;

describe the slum dwelling areas and mention urban planning.

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8.1 HUMAN SOCIETIES

Notes

Primitive humans passed the hunter gatherer stage once they discovered the comforts of
food sufficiency through agriculture, convenience of mobility with the discovery of the
wheel and the security of living in a group (see lesson-2). Humans felt the need for shelter
and settled life.
8.1.1 Temporary and permanent settlements
Settlement refers to an organized colony of humans with dwelling units (kutcha huts or
pucca houses) and roads they use for traveling. Hunters, herders, adventurers set up
camps for a limited period of time as temporary settlements. Inhabited villages and urban
agglomerates are permanent settlements. Few dwelling units forming a settlement is a
hamlet while large number of people settling in several clusters of buildings may be found
in the towns and metropolitan cities.
In the agricultural era (lesson-2), rural settlements predominated. With industrial revolution,
urban settlements, got established which are growing today.
8.1.2 Types of settlement: rural and urban
On the basis of size and functions, settlements may be categorized into:
1. Rural (villages) settlements
2. Urban (towns and cities) settlements
There is however, no characteristic criterion to distinguish between the rural and urban
settlements. Rural settlements are chiefly engaged in primary activities such as agriculture,
fishing, forestry, mining, artifact (craft) making, cloth weaving etc. Urban settlements indulge
in nonagricultural activities e.g. industries and manufacturing, trade and commerce, transport
and communication, defence and administration.

INTEXT QUESTIONS 8.1

1. Why did primitive humans decide to lead a settled life?
______________________________________________________________
2. Mention the basis on which settlements may be termed:
(i) temporary and permanent ________________________________________
(ii) rural and urban ________________________________________________

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8.2 URBAN SETTLEMENTS

8.2.1 What are urban settlements
Life in cities and towns is urban life. Traditional cities were usually walled. The walls
separated them from the villages which were mostly found in the countryside. Markets,
dwelling units, brick houses or concrete buildings for administrative bodies, religious
institutions (temples, mosques, gurudwaras, churches, synagogues and palaces and courts)
are common features of towns and cities. Commoners live towards the edges of cities as
they come into cities from villages in search of jobs. Urban people coming from rural areas
to large cities for employment settle down in shanties, at the periphery of cities. With time
and increase in population urban scenario has undergone a big change. Overcrowding and
abundance of concrete structures is a common feature today in most Indian cities.

Notes

Villagers are moving into cities in search of jobs, opportunities and better facilities.
The migration of rural population towards towns and cities in a country is leading to a
conspicuous chaos. As the villagers mingle with the already swollen urban population, they
start facing scarcity of water, sanitation, easily affordable housing, public transport, roads,
safe waste supply and clear air. Inspite of such difficulties, the influx of rural population into
cities is continuing and growing. It is estimated that by 2020, half of the Indian population
will be living in cities.
8.2.2 Occurrence of urban settlementspush and pull factors
The tendency to concentrate in towns and cities is called urbanization. In the 20th century
urbanization has taken place at such a fast pace that there has been an unprecedented
increase in urban population in almost all the countries of the world. Some of the important
reasons for migration of rural folk towards cities are listed below:
1. In search of better opportunities
You have already learnt that apart from agriculture and cottage industries for crafts, villages
do not offer opportunities for any other vocation whereas cities have many avenues for
jobs. Also schools are not well equipped and there are hardly any institutions for higher
studies.
2. For better life style
Superstitions, social taboos and criticism hold back forward-looking villagers from improving
life style so they rush towards cities. Also cities are consistently into trade and economic
expansion as well as territorial expansion. Fifty years ago Delhi was limited to old Delhi
and New Delhi fenced by the river Yamuna. Today Delhi has expanded in all the four
directions and extends upto a great distance beyond the eastern bank of river Yamuna.

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Notes

Environmental Science Senior Secondary Course

3. To overcome poverty
Poverty is rampant in most of the villages and villagers come to cities in search of work and
jobs. Because of poverty, slavery and prevalence of bonded labour are found in villages.
Young villagers run away to cities to break these shackles. Apart from these three major
pull factors villagers have also been pushed towards cities in times of war or famine or
natural disasters. Religious and political persecution are also common in villages. Racial
discrimination forces rural folk to move out of their villages. The factors which push rural
folk out of their villages and pull or draw them towards cities or urban areas are tabulated
in Table 8.1.
Table 8.1: Push and pull factors responsible for migration of villagers towards
cities
Pull factors
Villagers get attracted to cities for the
following.
1. Employm ent.

Push factors
Villagers are forced to move to cities
because of the following.

3. Better social amenities

1. Overpopulation (often one or more

members move out of large families
and then invite others to come to
cities)

4. Better life style

2. Religious/political persecution

5. Continuous trade and economic

expansion

3. Slavery/bonded labour

2. Better and more opportunities

6. Territorial expansion.

4. Lack of food
5. Racial discrimination
6. Natural hazards and climate change
7. Fragmentation of family owned land

Sometimes village youth go to cities to visit relatives and friends and stay on and settle
down.
More immigrants are attracted to bigger urban settlements.
8.2.3 Characteristics of urban communities
Urban communities are characterized by the following features:
(1) Social heterogeneity
People from diverse backgrounds and cultures throng the cities for better prospects and
like a melting pot get absorbed and live together as urban community. Social amenities
such as schools, hospitals, avenues for entertainment become readily available.
(2) Freedom from social control
Away from home, loneliness and sense of alienation bring about secondary associations.
Such associations flourish in the absence of control, back at home.
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(3) Voluntary associations

Close proximity, diversity and easy contact among socially diverse people bring them
closer. Clubs and associations are established to look into common requirements.
(4) Individualism

Notes

Multiplicity of opportunities, social diversity, lack of familial and social control over decisionmaking leads to more of self interest and facilitate decision-making by an individual and
choose ones career and actions by oneself.
(5) Social mobility
In a city no-one is bothered about the status at birth. Status in cities is largely based on
achievements, competence, efficiency and novelty.
(6) Availability of facilities
Diagnostic clinics, legal services, banks, commercial centres comprising of markets, malls
and departmental stores, hotels and guest houses are available to the city dwellers. It is
undoubtedly a better life for urban youth though a more stressful life. Based on the above,
table 8.3 highlights the major differences between rural and urban settlements.
The impact of migration from village to cities has not been only rosy as shown in table 8.2.
Table 8.2: Impact of migration from village to cities
Type of impact

At origin

Social

Men leave the

women behind

Economic

Environmental

At destination

Too many people

Cannot always cope with
education and health

No land for
farming
Crops decline
No personnel for
service

Unemployment
Economic insecurity
No professionalism/
vocation
Non taxable, low salary,
informal work

Slums develop

Pollution
Trash
Contaminated food and
water
Marginal land

The sadness of leaving the village are echoed in the poem given below:
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Notes

WHAT I LEFT BEHIND, WHAT I HOPE TO FIND

I left home, to come to school
I left farm, to come to food
I left my cows, my sheep,
But did not have time to weep.
Now I know why I cry tonight
Cos I know now what I left behind
and today, what I hope to find.
Cities full of cars and bikes
Restaurants and bars and roaring mikes
But I miss the vast sky
and my kites to fly
And my folks, my friends
Seem vanishing trends
So I cry tonight but what shall I gain
Tomorrow Ill struggle and then day after day again
Bharati Sarkar

INTEXT QUESTIONS 8.2

1. Define urban settlements.
______________________________________________________________
2. State any three factors which compel village youth to migrate to cities and towns.
______________________________________________________________
3. List any three typical features of urban settlements.
______________________________________________________________

8.3 RURAL SETTLEMENTS

8.3.1 What are rural settlements?
Primitive humans began to lead a settled life about 10,000 years ago. The settlements
were village habitations comprised of an enlarged primary group. Such village habitations
are persistent aggregates of human society. Simple living and compact organization
characterises rural societies.
Modern civilization considers urban societies to be superior to the rural societies as,
traditionally, common villagers are economically weak and inferior in skills and expertise.
Rural societies have low population density and limited opportunities. In India villages are
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significant as Indian culture is still preserved in villages. Most of the villages in different
parts of the country have retained their specific cultural and societal features. No wonder
India is the best example of unity in diversity.
8.3.2 Characteristics of rural settlements

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Notes

Rural communities possess special features:

1. Agriculture forms the dominant occupation. Even those not directly working in fields,
have occupations that are indirectly connected to agriculture. Village economy is
based on agricultural economy.
2. Joint family system: Joint family is a social and cultural institution more commonly
found in village communities than in cities.
3. Caste system: Social stratification based on castes is more pronounced in villages.
4. Jajmani system: Each village is grouped into (i) jajmans and (ii) service provider
castes who are paid in cash or kind. Jajmans are land owners. They come from upper
castes while service provider castes are at a middle or lower level.
5. Rural calendar: In Indian villages people understand the Indian samvat and the
Hijri calendars.
6. Simple living: God-fearing and tradition bound villagers lead simple lives untouched
by glamour of city life.
7. Poverty and illiteracy are because of uneconomic land holdings and poor productivity
due to fragmented and barren lands. Colleges, medical facilities, transport and civic
amenities are not available inspite of several rural development schemes of the
government.
8. Averse to mobility and social change: Orthodoxy, illiteracy, superstitions and fear
keep back youth from moving out or changing profession, caste and religion. Rural
social norms have a big influence in preventing violation of traditional norms of rural
society. The punishing authority of panchayats also contributes towards keeping back
rural youth from taking new initiatives or adopting any change.

8.4 DIFFERENCES BETWEEN RURAL AND URBAN

SOCIETIES
The rural life is a world apart from urban life. They are different in many ways as tabulated
below:

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Table 8.3: Differences between rural and urban settlements

S.
No.

Factor

Rural society

1.

Environment

Predominance of nature.
People directly related to
nature.

Human-made environment
predominant. Inhabitants isolated
from nature.

2.

Occupation

Agriculture- cultivators
and their families are in
majority. Few in nonagricultural pursuits.

Mostly industrial workers,

traders, professional and working
in offices. Mostly engaged
administration. All nonagricultural occupations.

3.

Community
size

Small

Much larger than rural community.

4.

Population
density

Comparatively lower
density of population

Large population density.

5.

Social
differences
and
stratification

Much less due to similar

vocation

Differentiation pronounced due to

work related differences in
earnings. Different strata of urban
society noticeable.

6.

Homogeneity
versus
heterogeneity

In racial, cultural and

Much heterogeneity in the same
psychological traits much country and same time.
homogeneity noticeable.

7.

Caste system

Rampant

8.

Mobility

Social mobility based on

Social mobility low.
achievement. Migration towards
Migration of population
towards cities mainly due villages low.
to poverty much more.

9.

Social
interactions

Primary contacts. More

durable and sincere
relationships due to
simplicity.

Notes

Urban society

Much eroded

Numerous contacts and wide

interactions. Casual, short-lived
relations-formal and mostly
superficial.

INTEXT QUESTIONS 8.3

1. What is a rural settlement?
______________________________________________________________
2. Why are villages suffering from poverty?
______________________________________________________________
3. Why are rural-folk more homogeneous socially?
______________________________________________________________

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8.5 AVAILABILITY OF LAND AND LAND USE IN

VILLAGES
Agriculture is the only major vocation in villages. Village community has (1) land owners
and (2) landless agricultural workers. The formers own land and grow crops with the help
of the latter.

Notes

As a consequence of rapid growth in population of a country, need arises for building

roads, dams, railway tracks, houses and industries. Land required for these developmental
activities is acquired from villagers by paying them monetary compensation. This has caused
colossal shrinkage of agricultural land and has also led to change in landscape.
8.5.1 Effect of modern technology on agriculture and rural life
The objective of agriculture, whether traditional or modern is to produce more crops by
providing factors necessary for increased crop production. Modern agricultural technology
has helped to achieve this objective, through the use of mechanised tools and implements,
expansion of irrigation facilities and use of agrochemicals such as fertilizers and pesticides.
Since most crop fields are in the countryside where farmers live in villages, modern
agriculture has had an adverse impact.
Intensive agriculture, which means enhancing crop productivity of the land with the use of
agricultural implements and agrochemicals, along with unplanned urbanization, deforestation
and industrialization have severely polluted the fresh water bodies and ground water
sources.
(1) Runoffs from crop fields carry soil, and chemicals used and pesticides and fertilizers to
water sources. This causes eutrophication and algal blooms about which you will have
learn in lesson 10. Eutrophication kills aquatic life including fish which are an important
source of food for villages.
(2) Excessive irrigation leads to water logging and salinisation of soil (excessive accumulation
of salt content in the soil which in turn adversely affects fertility).
(3) Excessive withdrawal of water from wells for irrigation generally deplete ground water
in many areas resulting in serious water scarcity. Pollution of lakes, rivers and other
water bodies, has deteriorated water quality in many areas leading to acute shortage
of safe drinking water. So has continued use of fertilizers and pesticides which pollute
ground water sources and deteriorate the water quality.
(4) Soil erosion, caused by the strike of sharp modern agricultural implements causes
siltation of rivers. Silt is the mud or soil that gets washed into water bodies as it gets
loosened (soil erosion). Siltation of rivers and lakes reduces their water retention capacity
and lead to flooding.
(5) Continuous cropping on the same land or on marginal lands for increasing food
production leaves no time for soil to revive through the natural processes. Cultivation
of mountain slopes also causes soil erosion. All this causes loss of mineral nutrients.
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8.5.2 Urban life provides facilities as well as difficulties: The Indian context
Urban life has its blessings and curses. India has a population of over 1.2 billion. Lack of
opportunities, poverty, conservative life style and orthodoxy force youth from villages to
migrate to cities and towns. The comparatively easier modes of travel in developing India
today, is another reason for the rural in villages. The job opportunities are limited in villages
and youth no longer wish to continue the occupation of their parents and forefathers. With
better exposure through radio, television and mobile phones providing easy connectivity
young villagers are lured towards cities and towns. Once they reach the cities they encounter
both facilities and difficulties. These are listed below:
Facilities
(i) Batter job opportunities.
(ii) Urban opportunities to about small bussiness.
(iii) Higher wages even unskilled labour is able to save money for sending home.
(iv) Easy availability of various kinds of goods and consumables.
(v) Better means of transport and communication.
(vi) Easily available electricity and tap water. In villages women have to walk long distances
to procure water. Time thus saved provides an opportunity to devote more time to
take care of children and adults can earn money through odd jobs.
(vii)Qualified doctors in hospitals and medical facilities are available.
(viii) Better educational facilities for adults and children are available.
Difficulties
(i) Lack of greenery and of open spaces.
(ii) Poor air quality. Villages are largely pollution free, while in urban areas, air is polluted
due to industries, automobiles, thermal power plants etc.
(iii) Scarcity of water and acute shortage lead to the growth of cheap lead to slums.
(iv) Lack of sanitation and hygiene.
(v) Overcrowding also causes several social problems.
8.5.3 Special problems of urban areas: Changes in life style and land availability
Rapid increase of urban population has necessitated expansion of urban limits. The
requirements of housing, construction of roads, industries and dams has led to encroachment
on agricultural fields and forests. Growing townships invade productive crop fields and
luxuriant forests. Concrete buildings come up on agricultural fields, grazing land and

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deforested areas. Land use changes irreversibly, land is degraded and affecting agricultural
fields on the benefit fringes of urban areas.
In most developing nations high rise condominiums (multistoried flats) are surrounded by
squatters and neighborhood slums which attracts new migrants to cities but inadequate
living space, lack potable water and light, unhygienic conditions from inadequate sanitation
and safe waste disposal causes suffering.

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Notes

Migrants from villages take no time to adopt urban life style which shows up in their
manner of dressing up, feeding habits and interaction with others.

8.6 INCREASED RESOURCE CONSUMPTION IN URBAN

AREAS
As large number of people permanently settle in small areas to form cities and towns, this
leads to increase in the consumption of natural resources. Land availability dwindles as
buildings for housing purposes come up. Increased water requirement of the growing
urban population causes a sharp decline in water availability. Excessive withdrawal of
ground water leads to ground water depletion. To meet the growing requirement of
water, result is drawn from distant areas thus disturbing the routes of natural water bodies
and affecting ecosystems.

8.7 WASTE GENERATION IN URBAN AREAS

Urbanization and industrialization produces colossal quantities of waste. Quantity of Solid
waste form domestic and industrial sources is growing problem. They may be biodegradable
when they may be used for generation of biogas. The nonbiodegradable waste is dumped
in land fills.
Liquid wastes such sewage from domestic sector and industrial effluents are usually
discharged without any treatment causing pollution of rivers and lakes. Sewage treatment
may help but is either lacking or seriously inadequate.
Urbanization leads to economic development. Increasing number of motor vehicles on the
road cause air pollution leading to congestion and traffic jams, apart from causing serious
problem of air pollution.
With rapid advancing urbanization, there is growing shortage of housing. This has led to
formation of large slums which lack basic facilities and infrastructure in cities. In fact, slums
represent the worst form of environmental degradation as they not only contribute towards
environmental pollution but also suffer from crime social problems. A large slum Dharavi
in Mumbai is the largest slum in Asia.

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8.8 SLUMS AND URBAN PLANNING

Migrant from villages coming to cities in search of jobs are generally poor and landless.
After reaching the city, they squat on vacant lands ultimately develops into a slum
which are also known as Jhuggi Jhonpri. Slums are a common feature of the
cities in developing countries.

These are self constructed shelters from scrap materials as plastic, wooden planks,
bamboos, jute, straw, plywood, bricks and mud etc. Often slums proliferate rapidly in
unplanned manner.

Slums are clusters of huts or homes in parts of cities. Kutcha or pucca houses, built
back to back and edge to edge often lack inadequate sun light, or fresh air due to poor
ventilation. Usually they are one- room tenements occupied by several inmates.

Absence of safe disposal of garbage and solid waste, lack of piped water supply and
drainages, electricity creates very precarious situation. Slums are squatter settlements.

Slums suffer from fire hazards particularly during summer due to short circuit and
carelessness of residents.

Notes

INTEXT QUESTIONS 8.4

1. What is intensive agriculture?
______________________________________________________________
2. State two major problems emerging from use of modern technology in farming.
______________________________________________________________
3. What are slums?
______________________________________________________________

WHAT YOU HAVE LEARNT

142

Society formation resulted when humans discovered the security that living in a group
provides. They discarded the hunting gathering culture and created human settlements.

Based on size, settlements may be rural and urban.

Life in cities and towns is urban life.

There are several factors which push rural fold out of villages and pull or attract them
to lead life in cities.

Social heterogeneity, individualistic life style, voluntary group formation, social mobility
and availability of facilities are characteristics of urban life.

Human Societies

But migration from villages to cities has had social, economic and environmental
implications.

Rural or village settlements have characteristics such as agriculture as vocation, joint

family system, caste system.

Poverty and illiteracy of villages makes them orthodox and superstitions.

Rural world and urban world differ with regard to environment, occupation, community
size, population density, social activities etc.

Modern technology has reached the farmers living in villages. Intentive agriculture has
helped in growing more food but use of chemical fertilizers and pesticides has degraded
not only agricultural fields but also environment per se.

Urban life in India has had is benefits like work opportunist, higher wages, availability
of consumables, comfortable day to day living.

Difficulties of urban life are lack of greenery, air pollution, overcrowding social problems.

Urbanisation has led to increased environmental resource consumption and excessive

waste generation.

Slums and squatter settlements are a reality in cities. These upset urban planning and
have specific environmental and social problems.

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Notes

TERMINAL EXERCISE
1. What are the types of human settlements?
2. List the reasons for which humans move from villages to cities.
3. State the differences between rural and urban settlements.
4. What are the facilities that rural youth come across when they migrate to urban areas?
5. Mention the difficulties faced by villagers who migrate to cities.
6. In what ways has the environment been degraded due to modern technology used in
agriculture?
7. Justify the following statement: Urbanization has led to increased resource consumption
and waste generations.
8. Write a short article on slums.
9. How has land use undergone changes with progressive urbanization.
10. Write an essay on problems of urban living.

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ANSWER TO INTEXT QUESTIONS

8.1
Notes

1. It gave them protection from dangers of hunting gathering life/security.

2. (i) Duration of settlement
(ii) Size
8.2
1. Living in cities and towns
2. Poverty/illiteracy/job opportunity/facilities/better social (any other)
3. Social heterogeneity/ lack of social control/voluntary associations/individualism/ any
other
8.3
1. Living in villages
2. Illiteracy/lack of job opportunities/agriculture only vocation/ superstition/ bonded labour/
any other
3. Bound together by language/ caste system/same vocation/ similar life style/ any other
8.4
1. Growing more crops on a small piece of land.
2. Depletion of natural resources/waste generation/ adverse effect of use of chemical
fertilizers/chemical pesticides use.
3. Clusters of huts or houses in parts of cities.

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Deforestation

Human Impact on
Environment

Notes

DEFORESTATION
In the previous lessons you have learnt about environment, its components and various
ecological concepts. You have also acquainted yourself with natural ecosystem and manmade ecosystems. Humans have altered the ecosystems according to their own needs
without thinking about the consequences. Their need combined with greed have caused
much damage to the environment, which will affect the coming generations. The expansion
of agriculture, urbanization and industrialization needed the land which was obtained by
large scale clearing of forests. The deforestation has changed the scenario of developed
and developing countries, and has brought out vast changes resulting into a various
environmental problems. In this lesson you are going to study about deforestation, its
causes and effect on environment.

OBJECTIVES
After completing this lesson, you will be able to:

define forest and describe the shrinking of forest cover throughout the world;

explain the various causes of deforestation;

give examples of exploitation of forest resources;

define biodiversity, give reasons for its rapid decline, express concern about the
consequences of biodiversity loss;

relate the fast depletion of wildlife and explain the concept of endangered,
threatened and exotic species and other forest resources due to deforestation;

describe how deforestation is contributing towards soil erosion, flash floods and
change in climate;

describe the impact of deforestation on tribal communities;

define desert and explain the causes of desertification; and give examples of
desertification in India;

identify the consequences of desertification.

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9.1 FORESTS

Notes

Forests are ecological as well as a socio-economic resource. Forests have to be managed

judiciously not only because they are source of various products and industrial raw materials
but also for environmental protection and various services they provide.
Approximately 1/3rd of the earths total land area is covered by forests. The forests provide
habitat for wildlife, resources such as timber, fire wood, drugs etc. and aesthetic environment.
Indirectly, the forests benefit people by protecting watersheds from soil erosion, keeping
rivers and reservoirs free of silt, and facilitate the recharging of groundwater. Forest plays
an important role in the cycling of carbon, water, nitrogen and other elements.
What is forest? Forest is a complex ecosystem consisting mainly of trees that
support a myriad forms of life. The trees are the most important component that help to
create a unique environment which, in turn, supports various kinds of animals and plants.
Trees are the prime producers for the forest, purify and cool the air and control the climate.
Forests may be subdivided into natural forests and plantations or man made forests. Natural
forests are forests composed of mainly naturally grown indigenous (local) trees while
plantations are forests established by growing trees by humans.
Climate, soil type, topography, and elevation are the main factors that determine the type
of forest. Forests are classified according to their nature and composition, the type of
climate in which they thrive, and its relationship with the surrounding environment. India
has a many types of forests: They range from rain forest of Kerala and North-East to
deciduous forests in the plains, mountain forests to alpine pastures of Ladakh and deserts
of Rajasthan.
9.1.1 Types of Forests
You have already studied the details of the major types of forests in India in
lesson- 6.(Recall Fig.6.2 of lesson-6)
9.1.2 Importance of Forests
Early life of humans on this planet began as forest dweller. In early days human were totally
dependent on forest for food, clothing, and shelter. Even after agriculture was started
humans remained dependent upon the forests for several of their needs. The source of fuel
wood and provide raw materials to various wood industries. Indian forests also provide
many other valuable minor products such as essential oil, medicinal plants, resins, turpentine
etc. Forests are renewable resources which provide a wide variety of commodities. Forests
satisfying aesthetic needs of humans and have been a source of inspiration for the
development of culture and civilization. Forests are home to a very large variety of plants,
animals and micro-organisms. This great richness of flora and fauna which has evolved

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over the years is an important part of nature. Forests provide habitat and food as well as
protection to wildlife species against extremes of climate.
Forests have great biological importance as reservoirs of genetic diversity apart from
playing an important role in regulating earths climate.

Human Impact on
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Notes

Forest carry out many important vital functions given in the following tables.
Table 9.1: Main functions of the forests
Functions

Benefits

Productive functions

Production of various types of wood, fruits and a wide

range of compounds such as resins, alkaloids, essential
oil, latex and pharmaceutical substances.

Protective functions

Provides habitats for various organisms conservation of

soil and water, prevention of drought, shelter against
wind, cold, radiation, noise, sounds, smells and sights.

Regulative functions

Absorption, storage and release of gases (most

importantly carbon dioxide and oxygen), water,
minerals, elements and radiant energy. All such
functions improve the atmospheric and temperature
conditions and enhances the economic and
environmental value of the land .Forests also effectively
regulate floods and drought and all the biogeochemical
cycles.

Timber
India and other tropical countries have particularly abundant timber and heartwood
resources. Timber accounts for 25% of all photosynthetic materials produced on the earth
and about half of the total biomass produced by a forest. A large number of trees are
commercially exploited for timber in different parts of India. Timber-based industries include
plywood manufacture, saw milling, paper and pulp, composite wood, matches, man-made
fibres, furniture, sports goods, and particle boards.
Medicinal plants
About 40% of all the drugs used throughout the world have active ingredients extracted
from plants and animals. Drugs which are derived from natural compounds amount to at
least $40 billion worldwide sales annually. For example quinine is used to treat malaria
(from the cinchona tree); Digitalis is used to treat chronic heart trouble (from the foxglove
plant, Cinchona officinalis); and morphine and cocaine are used to reduce pain;drug for
leukemia from Vinca rosea, taxol from Taxus brevifolia etc; and hundreds of life saving
antibiotics. In recent years more than 5000 species of flowering plants have been analysed
by scientists for the presence of valuable drugs.
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Asprin, which is probably the worlds most widely used drug was developed
according to a chemical blueprint, from a compound extracted from the leaves of
tropical willow trees.
Notes

INTEXT QUESTIONS 9.1

1. Make the list of plants used for medicinal purposes along with the botanical names
and the disease for which they are used.
______________________________________________________________
2. What are the main functions of forests?
______________________________________________________________
3. List various timber based industries.
______________________________________________________________

9.2 DEFORESTATION
Deforestation is a very broad term, which consists of cutting of trees including repeated
lopping, felling, and removal of forest litter, browsing, grazing and trampling of seedlings. It
can also be defined as the removal or damage of vegetation in a forest to the extent that it
no longer supports its natural flora and fauna.
The rapid rate of deforestation in the tropics is a key driving force in the yearly
increase of flood disasters.
Deforestation refers to the loss of tree cover; land that is permanently converted from
forest to non-forest uses such as agricultural pasture, desert, and human settlement.
In the beginning of 20th century about 7.0 billion hectares of forests were present over the
land of our planet and by 1950 forest covers was reduced to about 4.8 billon. If the
present trend continues forests will be reduced to only 2.35 billion ha hectares in 2000 A.D.
In a FAQ/UNEP study it was found that about 7.3 million hectares of rich tropical forests
every year and about 14 hectare of closed forest every minute are lost.

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Table 9.2: Forest cover as per 2001 assessment
Area (km2)

Class

Human Impact on
Environment

Percent of geographic area

I. Forest Cover
a) Dense

416,809

12.68

b) Open

258,729

7.87

Total Forest Cover*

675,538

20.55

47,318

1.44

Total Non-forest**

2,611,725

79.45

Total Geographic Area

3,287,263

100.00

Notes

II. Non-forest
Scrub

*includes 4,482 km2 under mangroves (0.14 percent of countrys geographic area)
**includes scrub

Forest Cover Assessment 2001

Dense forest
Open forest

Total forest cover = 20.55%

Non forest

Fig. 9.1: Forest cover in India

9.2.1 Extent of forest loss in India
India is an agricultural country. The country is losing its forest cover steadily because of
clearing forests of is done for agricultural purpose, cattle grazing and plantation crops such
as tea, coffee etc.
Deforestation is one of the most serious and widespread environmental problems which
India is facing. In India surveys conducted in early seventies and found a forest cover of
about 22.7%only instead of 33% considered desirable according to National. Forest
Policy.

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Notes

Environmental Science Senior Secondary Course

Soon after independence, rapid development and progress saw large forest tracts
fragmented by roads, canals, and townships. There was an increase in the exploitation of
forest wealth. In 1950 the Government of India began the annual festival of tree planting
called the Vanamahotsava. Gujarat was the first state to implement it. However, it was
only in the 1970s that greater impetus was given to the conservation of Indias forests and
wildlife. India was one of the first countries in the world to have introduced a social forestry
programme to introduce trees in non-forested areas along road sides, canals, and railway
lines.

9.3 CAUSES OF DEFORESTATION

The most common reason for deforestation is cutting of wood for fuel, lumber and paper.
Another important cause relates to the clearing of forest land for agriculture, including
conversion to crop land and pasture (Fig. 9.2).
Over-grazing
Agriculture

Causes
of
deforestation

Industry

Developmental project

Fuel wood

Fig. 9.2: Various causes of deforestation

The main causes of deforestation are:

150

agriculture;

shifting cultivation;

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demand for firewood;

demand of wood for industry and commercial purposes;

urbanization and developmental projects;

other causes.

Notes

(1) Agriculture
The expanding agriculture is one of the most important causes of deforestation. Man has
always modified the natural ecosystems in such a way that environment becomes more
favourable for crop growth whether using traditional or modern methods of agriculture. As
demands for agricultural products rises, more and more land is brought under cultivation
and for that more forests are cleared, grasslands and even marshes, and lands under water
are reclaimed. Thus there is much more ecological destruction than gain in term of crop
yield. The forest soil after clearing are unable to support farming for long periods due to
exhaustion of nutrients. Once the soils become unfit for cultivation, the area suffers from to
soil erosion and degradation.
(2) Shifting cultivation
Hunting and gathering has been the main form of sustenance practiced in the earlier periods
of human history. Shifting cultivation or Jhoom farming is a 12000-year old practice and a
step towards transition from food collection to food production. It is also known as slashuse (inAnnually
billion m3) aboutWood
Region and-burn
Total
wood ofWood
use (%)
method
farming.
5 lakhs
ha (hectares) of forest is cleared
consumption
for this(in
type
of farming.
In this type
of cultivation
there isFirewood
a limited use of tools with not very
billion
m3)
Firewood
Industrial
Industrial
high
level
of
mechanization.
However,
this
method
of54cultivation causes extreme
Global
3.2
1.5
1.7
46
deforestation,
as after 2-3
years of1.476
tilling, the land
the mercy of nature to recover.
Developing countries
1.8 (57%)
0.324
18 is left to82
Developed countries
0.224
84 local needs
16 or onsite demands to meet
This type1.4
of(43%)
cultivation1.176
was always
meant to fulfil
the requirements of the cultivating villagers. Even today, shifting cultivation is practiced in
the states of Assam, Manipur, Meghalaya, Mizoram, Nagaland, Tripura and Andaman
and Nicobar Islands.
(3) Demand for firewood
Firewood has been used as a source of energy for cooking, heating etc. Almost 44% of
the total global wood produced fulfils the fuel requirements of the world. Close look at the
pattern of utilization of wood produced will show that the developed countries utilize 16%
of their share for fuel requirements. India consumes nearly 135-170 Mt (Million tonnes) of
firewood annually and 10-15 ha of forest cover is being stripped off to meet the minimum
fuel needs of urban and rural poor.
Table 9.3: Use of wood

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(4) Wood for industry and commercial use
Wood, the versatile forest produce, is used for several industrial purposes, such as making
crates, packing cases, furniture, match boxes, wooden boxes, paper and pulp, plywood,
etc. 1.24 lakh ha of forest have been cut for various industrial uses. Unrestricted exploitation
of timber as well as other wood products for commercial purposes is the main cause of
forest degradation. The paper industry accounts for about 2% of countrys annual
consumption of wood and 51% this requirement is met by bamboo wood. This has led to
the depletion of bamboo stocks in most of the peninsular India. For example the apple
industry in the Himalayan region has led to the destruction of fir and other tree species, for
making wooden boxes used for transporting apples. Similarly, plywood crates were used
for packing particularly tea and other produce.
(5) Urbanisation and developmental projects
Often urbanisation and developmental activities lead to deforestation. The process of
deforestation begins with building of infrastructure in the form of roads, railway lines,
building of dams, townships, electric supply etc. Thermal power plants, mining for coal,
metal ores and minerals are also important causes of deforestation.
Nowadays you must have heard about the Tehri power project which is a 260.5m high
earth and rock fill dam near the Tehri town in Garhwal Himalayas. The project site is
situated a little downstream the junction of Bhagirathi and Bhilganga rivers. An estimated
4,600 ha of good forest land will be submerged under water. This has displaced an estimated
3,500 odd families.
(6) Other causes
Recent developments everywhere in world have caused large scale environmental
degradation, especially in tropical forest areas. The large amounts of resources living and
nonliving (minerals, river, land) found in these forests have attracted both industry and
other developmental agencies, which have severely depleted forest cover.
Forests may sometimes suffer from natural calamities such as overgrazing, floods, forest
fires, diseases and termite attack.

9.4 FORESTS AND TRIBAL SOCIETY

About 4% the worlds population lives in special territories .These indigenous or tribal
people have claims on a particular place; they have cultural, spiritual and economic ties
with the particular area and in most cases they have ability to manage the area and sustain
it. In this way they protect the biodiversity of that particular area and the local culture,
including knowledge and resource-management skills of the local community.
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For example, the tribal people knew the agricultural practices which were ecologically
sound and these were passed from generation to generation for many centuries. They
knew how to grow different kinds of food and fibre crops simultaneously on the same
plots and keep the land productive for several years in a row, and then plots were left to
recover for several years to grow back into forests, before clearing the area again to begin
the cycle afresh.

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Notes

In India the tribal populations constitute about 7% of the Indian population. They
live in some 450Communities or tribal units of different sizes.

INTEXT QUESTIONS 9.2

1. List the causes for deforestation.
______________________________________________________________
2. Where is Tehri power project?
______________________________________________________________
3. List the names of the Indian states, where shifting cultivation is still practised.
______________________________________________________________
4. Give reasons how the tribal communities were able to live in forest without harming it.
______________________________________________________________
5. What percentage of total wood produced in developing countries is utilized for fuel
requirement? (Refer to table 9.3).
______________________________________________________________

9.5 CONSEQUENCES OF DEFORESTATION

Deforestation affects both physical and biological components of the environment.

Soil erosion and flash flood

Climatic change

Loss of biodiversity

(1) Soil erosion and flash flood

A shrinking forest cover coupled with over exploitation of ground water has accelerated
erosion along the slopes of the lower Himalayas and Aravali hills, making them prone to
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landslides. Destruction of the forests has altered rainfall pattern. In 1978 India suffered
some of the worst flooding in its history. There was two days of heavy rainfall and 66,000
villages were inundated, 2,000 people drowned, and 40,000 cattle were swept away. In
2008 Bihar state suffered worst flood in the river kosi. Several lives were lost and a huge
number of cattle were swept away. Lack of forest cover has resulted in water flowing off
the ground, washing away the top soil which is finally deposited as silt in the river beds.
Forests check soil-erosion, landslides and reduce intensity of flood and drought.
The loss of top soil is in India, is 18.5% of the global soil loss. This is indeed very
serious, considering the fact that India has only 2.4% of the land area of the world.
(2) Climatic change
Forests enhance local precipitation and improve water holding capacity of soil, regulate
water cycle, maintain soil fertility by returning the nutrients to the soil through leaf fall and
decomposition of litter. Forests check soil-erosion, landslides and reduce intensity of flood
and droughts. Forests, being home of wildlife are important assets of aesthetic, touristic
and cultural value to the society.
Forests have profound effect on the climate. Forest absorbed carbon dioxide from the
atmosphere and help in balancing carbon dioxide and oxygen in the atmosphere. The
forests play a vital role in maintaining oxygen supply in the air, we breathe. They also play
a vital role in the regulation of water (water cycle) in the environment and act as environmental
buffers regulating climate and atmospheric humidity.
Heat build-up in the atmosphere is one of the important problems of the century known as
green house effect is the partly caused by the result from deforestation. The entire
Himalayan ecosystem is threatened and is under severe imbalance as snow line has thinned
and perennial springs have dried up. Annual rainfall has declined by 3 to 4%. Chronic
droughts have begun even in areas like Tamilnadu and Himanchal Pradesh where they
were not known earlier.
(3) Biodiversity
Biodiversity include all variety of life forms. Biodiversity - (biological diversity) is a
measure of variation, the number of different varieties, among living things. Biodiversity
can be expressed in number of ways, which includes the number of genetic strains
(differences) within species and the number of different ecosystem in an area. The most
common expression of biodiversity is the number of different species, within a particular
area (local biodiversity), or in a specific habitat (habitat biodiversity) or in the world (global
biodiversity). Biodiversity is not static. It changes over the time during evolution new species
have come up while some species become extinct.
Our knowledge is incomplete at the global level; nearly 1.4 million species have been
identified. Different species inhabiting the earth have been estimated to vary between 10

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and 100 million. There is lot of concern about preserving biodiversity. You will study more
about biodiversity conservation in lesson 15. The one good reason for preserving
biodiversity is that it provides wide variety of products for human use and welfare. It is a
great potential resource for agriculture, medicine and industry.
There are several causes for biodiversity loss:

hunting, poaching and commercial exploitation.

elimination and disturbance of wildlife habitats.

selective destruction of habitat/ life forms.

domestication.

introduction of new alian species in new area which threaten the indigenous species.

use of pesticides.

pests, medical research and zoos.

Human Impact on
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Notes

All the above factors adversely affect biodiversity.

9.5.1 Extinct species
Ultimate fate of every species is extinction but after industrialization this rate has increased
tremendously. The extinct species only exist in museums and photographs. The most noted
example of extinct species is passenger pigeon.
Threatened species
Several plant and animal species are threatened by the possibility of being on the verge of
extinction but the seriousness of this threat varies. International Union of Conservation of
Nature (IUCN) has categorized threatened species into four categories which are:
(i) Endangered

A species is considered endangered when its numbers are few and

its homeland is very small, or both and if special protection is not
given it may become extinct .for example the lion tailed monkey
from rain forests and Sholas of south India.

(ii) Rare

These are those species whose number is few or they live in such
small areas or such unusual environment (endemics), that they could
quickly disappear.The Great Indian Bustard (Ardeotis nigriceps )
is an example of rare species of India. (Fig. 9.3)

(iii) Depleted

These are the species whose numbers are greatly reduced from
those of the recent past, and they are continuing to decrease. It is
the continued decrease, which is the main cause of concern. Animals/
plant in this category can quickly change to a rare or endangered
category. In the past few years, the fur of the clouded leopard
(Neofelis nebulosa) was sold illegally in Kashmir markets.
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(iv) Indeterminate Those species that seem to be in danger of extinction but their true
information regarding their status is not known are the indeterminate
species. The snow leopard (Leo uncia) was classified as
indeterminate species in 1968, and was declared endangered in
1970. You probably know that the snow leopard is hunted for its
thick beautiful fur.

Fig. 9.3: Great Indian bustard

9.5.2 Loss of wild life
Over the past 2000 years, 600 species of animals have become extinct or are going to be
extinct from the earth. Similarly, about 3000 species of plants need to be conserved. The
shrinkage of green cover has adverse effects on the stability of the ecosystem. Poaching is
another factor causing depletion of wildlife. The roll call of victims is endless. In Africa, in
recent years, nearly 95 per cent of the black rhino population has been exterminated by
poachers for their horns and over one third of Africas elephants have been wiped out for
ivory. The scarlet macaw once common throughout South America has been eliminated
from most of its range in Central America. Several species of spotted cats such as the
ocelot and jaguar are in danger of extinction due to demand of their fur.
9.5.3 Loss of wildlife in India
India has nearly 45,000 species of plants and 75,000 species of animals. This biological
diversity ought to be preserved for maintaining stability of ecosystems. Deforestation coupled
with desertification has destroyed the natural treasure of the earth to a large extent.
The population of elephant, lion and tiger is fast diminishing. Cheetah is already extinct.
Elephants once found all over India have now disappeared from Andhra Pradesh, Madhya
Pradesh and Maharashtra. The Asiatic lion which was very common in Asia has practically
vanished from Asia except for a few hundred sq km (square kilometer) of Gir forest in
India.
In India four species of mammals and three species of birds have been extinct in the last
100 years. Another 40 species of mammals, 20 species of birds and 12 species of reptiles
are considered highly endangered due to overexploitations, of forests.
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INTEXT QUESTIONS 9.3

1. Name an endangered species in India.
______________________________________________________________
2. List the main causes for the depletion of wild life.
______________________________________________________________
3. Name the mammal that is already extinct from India.
______________________________________________________________
4. Name the mammal that was once common in Asia is now found in few hundred
kilometer at Gir forest in India?
______________________________________________________________
5. Define biological diversity.
______________________________________________________________

Notes

9.6 DESERTIFICATION
What is desertification? It can be defined as the diminution or destruction of the
biological potential of the land which can ultimately lead to desert like conditions.
The arid and semi-arid areas where climate is dry, restoration is very slow, mining and
overgrazing etc. adds to several other desertification pressures. Desertification is a systemic
phenomenon resulting from excessive felling of trees which manifests itself in the loss of soil
fertility, high wind velocity, low precipitation, increasing aridity and extremes of temperatures
in the affected area.(Fig.9.4)

Fig. 9.4: Excessive felling of trees leads to desertification

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Desert supports very little of vegetation and animals which are especially adapted to
extremely unfavorable conditions. Although desertification can develop from natural causes
alone, in a majority of instances human intervention promoted arid conditions in an already
dry areas. This can happen in any climatic zone or ecosystem, resulting from exploitative
interaction of man with the natural ecosystem. Most of the deserts of recent origin have
resulted form any one or more of the following human activities.
(i) Uncontrolled and overexploitation of grazing land, indiscriminate cutting of trees and
forest resources leading to drought, soil erosion, deterioration of soil fertility which
results in stunted plant growth.
(ii) Excessive mining in arid and semi-arid regions for extraction of minerals, coal or
limestone resulting in loss of trees, and green cover, and leading to total destruction of
conditions conducive to vegetation growing.
(iii) Uneconomic land use for agriculture by cultivation on marginal lands affecting adjacent
fertile lands and causing soil erosion.
(iv) Intensive and uneconomic exploitation of water resources leading to fall in water table,
seepage and problems of excessive salinisation of soil.
Table 9.4: Extent and causes of land degradation of the world
Area

Causes of land degradation

580 million ha Deforestation -- Vast reserves of forests have been degraded by

large scale logging and clearance for farm and urban use. More than
200 million ha of tropical forests were destroyed mainly for food
production.
680 million ha Overgrazing About 20% of the worlds pasture and range lands
have been damaged. Recent losses have been most severe in Africa
and Asia.
137 million ha Fuel wood consumption About 1730 million m3 of fuel wood are
harvested annually from forests and plantations. Wood fuel is the primary
source of energy in many developing regions.
550 million ha Agricultural mismanagement Loss of soil due to water erosion is
estimated at 25,000 million tonnes annually. Soil salinization, water
logging, chemical degradation and desertification affect about 40 million
ha of land globally.
19.5 million ha Industrialization and urbanization Urban growth, road
construction, mining and industry are major factors in land degradation
in different regions. Valuable agricultural land is often lost.

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9.6.1 Extent of desertification
About 76.15% of the total Indian desert area has resulted from manmade desertification
process. Another 19.5% of the total area is subjected to medium or slight desertification.
This area is concentrated mostly along the eastern Rajasthan in the north-east to southwest zone parallel to the foothills of Aravalis.

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Notes

Most of the deserts, in India are found in the states of Rajasthan and Western Gujarat,
where about 23.8 mha area has been affected by desertification. About 4.34% of this area
lies in the extreme West of Rajasthan in Jaisalmer district. This desert is concentrated
along a belt in Ganganagar, Churu, Bikaner, Jaisalmer, Barmer, Jodhpur, Jalore, Jhunjhunu
and Nagaur districts. The predominant processes of desertification in this belt are the
expansion of sand cover and shifting sand dunes by wind erosion.
Natural desertification
In the Asia and pacific region an area of about 4.361 lakhs ha has resulted from
natural desertification. These areas can be classified as subtropical, cool coastal,
rain shadow and interior continental deserts. Besides these, Polar regions of the
world also represent a type of desert, where water is no doubt present in plenty, but
being in the form of ice, it is not available for plants and animals. The Gobi desert of
north western Asia is a cold desert. The Ladakh region of Jammu and Kashmir
covering an area of 0.7 lakh sq. km. and located at an altitude of about 11,000 feet
where extreme cold conditions prevail for about 5-6 months in a year, is also a cold
desert.
9.6.2 Thar DesertA case study
The Thar Desert exhibited spectacular biological diversity because of its evolutionary history
and geographical location. This is a extensive region of sandy desert in northwestern India
and eastern Pakistan. The Thar Desert is about 805 km long and about 485 km wide.
Rainfall is sparse averaging from 127 to 254 mm annually and temperature rises as high as
52.8oC in July.
(i) Plants
Ecologically, vegetation of the major part of Thar Desert region falls under the category of
thorn forest type. However, the natural vegetation cover has become progressively
transformed due to prolonged and intense human interference. Nevertheless, natural
vegetation makes a substantial contribution to the productivity of trees like Khejri which
are highly valued and conscientiously maintained. There are as many as 700 species of
plants amongst which grasses alone account for 107 species. Large-scale destruction of

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natural vegetation from this part of the country is due to heavy pressure of overgrazing by
livestock, making regeneration of plants process in the desert very difficult.
Human activities and - more fundamental - underlying structural factors and material
processes in our society are causing species to vanish at a rate unequalled since the
doomsdays of the dinosaur. Theres no time to waste. We must protect biodiversity now,
for our next generation.
(ii) Animals
Thar desert is fascinating. The Asiatic lion, used to inhabit the plains of Rajasthan, Punjab
and Sind in the recent past. It is on record that the last lions occurring in the desert were
shot during 1976. The cheetah now extinct in India was at one time found in the Kathiawad
region. Similarly, leopards and caracal lynx, the wild boar, wild ass, Asiatic wolf, etc. have
also met the same fate. Among other mammalian fauna, Indian gazelle, blue bull and black
buck are also in the list of endangered animal species.
Predominant bird species are also very scanty, particularly in sandy habitats of western
Rajasthan. The great Indian bustard, houbara, and lesser florican populations in the Thar
Desert are dwindling as compared to that in the recent past. Pea-fowl, being a national
bird, is well protected by people.
Among reptiles, two species of crocodiles and turtles are now restricted to Jawai-dam in
Sirohi district at the foot hills of Aravali. The large terrestrial reptile, the rock python found
on the foothills of Aravali is also vanishing from the desert.
Thus, looking at the past history of Thar desert, a large number of animals are at the verge
of extinction and some .have vanished.

INTEXT QUESTIONS 9.4

1. What is desertification?
______________________________________________________________
2. List any three human activities that have resulted into desert formation.
______________________________________________________________
3. Name the two states where most of the deserts found in India.
______________________________________________________________
4. Name a mammal, a bird and a plant that were once found in large numbers in thar
desert but are now in the list of endangered species.
______________________________________________________________
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WHAT YOU HAVE LEARNT

Forests are the backbone of the life forms and the life on earth is sustained through
them.

There are three major functions of the forests i) productive functions .ii) protective
functions iii) regulative functions.

Timber and several models obtained from plants for medicine are still provided by
forests.

Tribal people totally depended on forests for food, shelter and clothing; in turn they
also conserve the forests.

Deforestation of forests is caused due to shifting cultivation, demand for timber, for
paper and pulp, commercial wood and fire wood, and mining operations.

Deforestation also causes soil erosion and floods, climatic changes, loss of wild life.

Loss of biodiversity during deforestation is immense because several unknown species

of biota is lost forever from our planet earth.

Extinct species are those that were unable to survive in the changed environment and
thus perished.

Threatened species are likely to become extinct if their environment deteriorates further,
endangered species are few in number and their homeland is very small and any
deterioration in environment can make them extinct.

Depleted species are those whose number have decreased in the recent years and are
continuing to decrease. Indeterminate species are those species whose status is not
known due to lack of information.

Desertification is a natural phenomenon but it is often accelerated by human activities.

they are uncontrolled grazing, indiscriminate cutting of forests, excessive mining,
uneconomic use of agriculture land, exploitation of water resources.

Deforestation and desertification are two interlinked problems which have arisen from
the overexploitation of natural resources through human activities causing irreparable
damage to earth.

Notes

TERMINAL EXERCISE
1. Write any three functions of the forest, which function you think, is the most important
and why?
2. Discuss why deforestation is one of the most important factors for wild life loss in the
whole world.
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3. Match the definition of words given in column A with column B
Column A

Column B

(a) Rare species

i)

A species is considered endangered when its numbers

are few and its homeland is very small, or both and if
special protection is not given it may become extinct

(b)Indeterminate species ii)

These are those species whose number is few or they live

in such small areas or such unusual environment
(endemics), that they could quickly disappear.

Notes

(c) Endangered species

iii) These are the species whose numbers are greatly reduced
from those of the recent past, and they are continuing to
decrease.

(d)Depleted species

iv) Those species that seem to be in danger.

4. Make a project on habitat destruction and wild life loss by giving at least example of
five animal species and five plant species, try to give photograph/drawing of the species.
5. Make a list of extinct animal and plant species from India by going through various
books and magazine.
6. The development projects have harmed the tribal society the most give your views
on the above given statement.
7. Discuss deforestation results in desertification.
8. Write an essay on the importance of forest in human life. Support your answer with
diagram.

ANSWER TO INTEXT QUESTIONS

9.1
1.

Plant

Medicinal use

a. Cinchona Officinalis

Treatment of malaria

b. Dititalis purspusla

Treatment of chronic heart disease

c. Vinca rosea

Treatment of cancer

d. Taxus brevifolia

Treatment of cancer

2. Protective function, productive function and regulative function.

3. Plywood manufacture, saw milling, paper and pulp, composite word, Matches, Man
made fibres, furniture, sport goods and particle boards.
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9.2
1. Agriculture, shifting cultivation, demand for fire wood and timber, development projects
requiring land and raw materials.
2. Near Tehri town, at the junction of Bhagirathi and Bhilganga.

Notes

3. Manipur, Meghalaya, Mizoram, Nagaland, Tripura, Andman and Nicobar Islands.

4. Tribal people used ecologically sound agricultural practices and the knowledge of
such practices were passed on to the next generations for centuries.

they grew multiple crops simultaneously for some years and then plots were left to
recover and grew back into forests

they have cultural and economic ties with the forest they live in and have the ability
to sustain it and protect it.

5. 82%
9.3
1. Lion tailed monkey
2. Commercial exploitation

Introduction of exotic species

Habitat loss/ disturbance in habitat

Domestication

Use of pesticides

3. Cheetah
4. Asiatic Lion
5. All forms of life including plants, animals and micro organisms in nature constitute
biological diversity.
9.4
1. Destruction of the biological potential of the land which can lead to desert like
conditions.
2. Over exploitation/ uncontrolled grazing/ indiscriminate felling of trees / intensive and
uneconomic exploitation of water resource leading to fall in water table/ uneconomic
land use for agriculture. (Any three)
3. Rajasthan and Gujarat
4. Wild boar/wild ass Mammal
Great Indian bustard Bird
Kehjri Plant
163