2

Ecosystem

2.1 INTODUCTION
All living organism interact with their natural environment. Interaction results in sustenance o
functional unit in which
life. The
unit that sustains the life is called ecosystem. It is a
natural
all living organism (plants, animals and microorganisms) and non li'ving component (ar, wate
soil and energy) of the environment are linked together through energy flow and nutrient cycle.
the environment
A nutrient cycle is a repeated pathway of a particular nutrient or element from
include the water cycle,
through one or more organisms and back to the environment. Examples
carbon cycle, the nitrogen cycle and the phosphorus cycle.
is derived
The ecosystem was coined by A.E. Tansley in 1935. The word ecosystem
term
of nature or units and System
from Eco +system, Eco' embodies Biotic +Abiotic components
defines ecosystem as a basic functional
means dynamic functional attributes. E.P. Odum (1971) and
factors interacting with each other
unit of nature which consists of living and non living elaborated
for the development and maintenance of the system. In 1975, he further
necessary
the term as "Any unit or area which includes all living organisms,
interacting with abiotic component
and exchange
that the flow of energy leads to clearly defined trophic structure, biotic diversity
so
for
within the system". The alternative term
of materials in living and non living component
used Russian scientist Sukachev is Geobiocoenosis.
by
ecosystem

2.2 STRUCTURE OF ECOSYSTEM

in figure 2.1., and can be categorize
The structure of the Ecosystem is diagrammatically presented
into two components:
1. Abiotic component:
2. Biotic component:

2.2.1 Abiotic Component

life such as air, water, soil and energy:
It includes factors which have no
and organic substances like hu
1. Inorganic substances like carbon, itrogen, water, etc.
protein, carbohydrate, etc.
 26 Basic Environmental Studies
C l i a t i e condition such as temperature, light, moisture und pH.

Solar Radiation Autotrophs Heterotrophs Heat

Green Plants, Animals,
zooplanktons etc.
Material Input Phytoplanktons
Processed Energy
and Material
Plant Dispersal Decomposers
Detritivores, Plant Dispersal
Animal Migration- Fungus etc. Animal Migration

Flg. 2.1. Diagramatic representation of ecosystem

showing interaction of biotic and abiotic factor

2.2.2 Biotic Component

It consists of all living organism that can be categorized into following groups:
1. Autotrophs: Those organisms which can produce their own food like plants.
2. Hetertrophs: Those organisms which depend on others for their food like animals.
They are also called as Phagotrophs.
3. Osmotrophs or Saprotrophs: They are also called as decomposers which are mainly
fungus, bacteria and other microorganisms. They
depend upon the dead and decaying
parts of plants and animals.
Biotic component includes living
organisms like plants, animals and decomposers. They are
further categorized into three
groups on the basis of their functional attributes such as
consumer and decomposer. producers,
(a) Producers: The green plants, phytoplankton's and algae are considered as
or
autotrophs because they can synthesize their own food by producers
bacteria also included in the
are
photosynthesis. Chemosynthetic
producers. They make their own food by extracting
energy (e-) from chemical oxidation. In terrestrial
herbs, shrubs and woody ecosystem, the main producers are
plants. However, in the marine or freshwater, the main
are
phytoplankton's or algae. producers
 Solar Energy
Abiotic Factors
Heat Loss (CO2. Op. N2. Minerals, etc.)
H e a t Loss

Heat Loss

Decomposers Producers
(Detritivores, Funguus, (Plants, Algae)
Microbes)

H e a t Loss

Consumers
Heat Loss
(Herbivores, Carnivores)

Fig. 2.5. Energy flows and material cycles

their food.
(b) Consumers: They depend directly or indirectly on the autotroph/producer for
The consumers can be divided into two groups:
feed plants or animals or
() Macroconsumer or Phagotrophs: These organisms on
both. The order in which they are present in the food chain is herbivores or primary
consumers which feed on plants like cow, sheep. Primary carnivores or secondary
feed on herbivores, e.g. Wolves. Secondary carnivores or Tertiary
consumer
consumers
on both herbivores
feed on secondary consumers, e.g. Lion. Those animals which feed
and carnivores are called omnivores, e.g. Human.
which includes
(i) Microconsumer: They are also known as decomposers or saprotrophs
dead plants or animals. The
bacteria, fungi and microorganisms which decompose
their biomass. Animals like earthworm
decomposed material is reused by plants to form
the organic matter.
or certain nematodes also help to decompose

2.3 TYPES OF ECOSYSTEM

On the basis of origin, there are two type of ecosystem such as:

1. Natural ecosystem 2. Man made or artificial ecosystem

2.3.1 Natural Ecosystem

Such ecosystem operates under natural condition without any interference of human activity.
iS further classified into two types on the basis of type of habitat.
28 Baric Erviro

Fig. 2.2. Natural terrestrial ecosystem (Forest)

(a) Terrestrial ecosystem: It includes forest, grassland, desert, etc. (Fig. 2.2)

Fig. 2.3. Natural aquatic ecosystem (Lake)

(h) Aquatic ecosystem: It includes water bouIES, Smai or large, stagnant or flowing Itis
broadly divided into freshwater andmarine ecosystem. The fresh water ecosystem includ
includes ocean and estuaries
includes
river, lakes, etc. and marine (Fig. 2.3).
pond,
 Ecosystem 29

Fig. 2.4. Artificial (man-made) terrestrial

ecosystem (Rice Fields)
2.3.2 Artificial Ecosystem
Such ecosystems are artificially maintained and manipulated by human beings. It includes
agricultural
fields like rice or wheat fields. Here human beings control the physico-chemical environment
and also the other biotic component of the ecosystem (Fig. 2.4).

2.4 COMPONENT OF ECOSYSTEM

The structural component of ecosystem can be broadly classified into biotic and abiotic
components
through which energy and nutrient flow. Fig. 2.5 represents the energy flow and nutrients cycle
through biotic and abiotic components.

2.5 SIZE OF ECOSYSTEM

The size of ecosystem can vary from very small like cow dung to very large and complex like
sea, forest or biosphere. Sometimes, the ecosystem is present within the ecosystem. For example.
cow dung ecosystem may be present in forest
ecosystem which is contained in the biosphere.
Some ecosystem show well defined boundary like pond but other system do have
not a sharp
boundary. Latter type, of ecosystems is separated by a transition zone caled ecotone where
characters of both the ecosystems are present. The diversity in the ecotone is more as compared
to the ecosystem flanking it.

2.6 FUNCTION OF ECOsvSTEM

As ecological point of view, energy flow follows first law of thermodynamics and shows conversion
from one form of energy to another with reduction in capacity to do work. On the other hand,
the energy is utilized to run the nutrient cycle whereby nutrient gets incorporated into organism
DOuy due to anabolic activities as well as some energy and nutrients liberated from body as a
result of death of an organism.
30 Basic Environmental Studies

invOIves the volume and the

The study of the functional aspect of ecosystem rate at which
a d the rate at which energy floue
clc.) circulate Vs through
material ( Nutrient as C, H, O, N. P.
of productivity and food chain.
it. It can be understood through concept
Flow in the Ecosystem
Nutrient Cycle & Energy
their processes and human also affect ecosystem
affeet human life by .
Every cosvstem
evolution of both entities go hand in hand. The process
by
their activities. In this way. operating
as nutrient Cyele and energy flow. The examples of nutri
in aosvstem can be classified
cle are the water cycle. the carbon cycie, tne oxygen cycle and the nitrogen cvcle Th
The
energy flow is unidirectional process that starts from sun and after reaching earth again is
sent back to space. During this process some amount of energy is trapped and utilized t
run these nutrient cycles on earth. The energy is stored in food material (glucose, starch, fat

etc) or biomolecules like skin (keratin) chitin, Cellulose forming wood or leaf of trees.
Though. every ecosystem is controlled by these cycles and energey flow, but in each ecosystem
its abiotic and biotic features are distinct from each other. All the functions of the ecosystem
are in some way related to the growth and regeneration of its living organisms. These processes
depend on energy from sunlight. During photosynthesis carbon dioxide is taken up by plants
and oxygen is released. Animais depend on plants for food and oxygen.
The water cycle depends on the rainfall, which is necessary for plants and animals to live
The energy cycle recycles nutrients into the soil on which plant life grows. Our own lives
are closely linked to the proper functioning of these cycles of life. If human activities go on
altering them, humanity cannot survive on our earth.

Water Cycle/Hydrological Cycle

The natural sequence through which water passes into the atmosphere as water vapor.
precipitates to earth in liquid or solid form, and utimately returns to the atmosphere through
evaporation. In this cycling process water moves through hydrosphere, lithosphere and biosphere.

Nitrogen Cycle
The Nitrogen cycle is a sequence of events by which atmospheric nitrogen and nitrogenous
compounds in the soil are converted, as by nitrification and nitrogen fixation, into substances
that can be utilized by green plants, the substances returning to the air and soil as a result
of the decay of the plants and denitrification.

Energy Flow
It refers to the flow of energy through a food chain. Energy from sunlight is converted by
plants themselves into growing new plant material which includes leaves. flowers, fruit, branches
trunks and roots of plants. Since plants can grow by converting the sun's energy directly into
their tissues, they are known as producers in the ecosystem. The plants are used by herbivorous
 Ecosystem 31

als as food,
nimals which gives them energy. A large part of this energy is used up for day to
anctions
day functions of these animals such as
breathing, digesting food, supporting growth of tissues,
blood flow and body temperature.
maintaining

26.1 Productivity Ecosystem

of
ductivity of ecosystem refers to the rate of production of organic material from inorganic
Produc

uponents, i.e. the total amount of organic matter accumulated in any one unit time. It can

be observed at three levels;

. Primary Productivity
2 Secondary Productivity
3. Tertiary productivity

2.6.1.1 Primary Productivity

The rate at which radiant energy (Sunlight) is stored in the producers (green plants and
photosynthetic microbes like bacteria and blue green algae) by the process of photosynthesis
and chemosynthesis. It is further divided into two types
(a)Gross primary productivity: It is defined as the total rate of photosynthesis which
includes the organic matter (Synthesized and stored food) used up in the process of
respiration during the measurement period.
rate of storage of organic matter (fat,
(b) Net primary Productivity: It is defined as the
utilization by plant
protein and carbohydrate) in the plant tissue in excess of respiratory
during the measurement period.

2.6.1.2 Secondary Productivity

level and can be defined as the rate
It refers to the productivity at heterotrophs or consumers

consumer utilizes food materials in the respiration

of the energy storage at consumer level. The
assimilation was used by
and converts the food material into different tissue. The term
process
the Odum instead of productivity.

2.6.1.3 Net Productivity

the by It is
matter which is not utilized
consumers.

t refers to the rate of storage of organic

producerswhich has been leftover by the consumers.
tne rate of increase of biomass of primary
t is expressed in C g/m-/day.

2.6.2 Food Chain

into the plants through photosynthesis by
TE transfer of energy from gets assimilated
sun
matter. This organic matter is passed
material (C, H, O) into organic
Onverting inorganic raw with repeated eating and being eaten
through a series of organisms
Ogreen plant source transfer 80-90 % of the potential energy
is lost
called as food chain. At each level of energy
 32 Basic Environmental Srudies

in the form of heat energy. Organisms, whether dead or living, serves as food lor oner organism-

As a result. there is zero wastage in the-ecosystem.

Concept of Pyramid
Graphic representation of flow of energv and nutrient cycling
or material transier
through
various food chains (Trophic levels) is called Pyramid. The concept of pyramna was proposed

of pyramid are important.

Dy Cnarlas Eton. To study any ecosystem, three kinds
1. Pyramid of energy: It show always upright condition.
. Pyramid of Bionmass: It may show upright (grassland/forest ecosystem) or inverted

(pond ecosystem).
3. Pyramid of Number: It may show upright (grassland/pond ecosystem) or inverted

(forest ecosystem).
The Food chain can be visualized as into two types:

2.6.2.1 Grazing Food Chain

Grazing food chain starts with green plants, moves to herbivores and then to carnivores i.e.
animal eater. Such food chain depends on the influx of the soBar radiation. Example of grazing
food chain Fig. 2.6:

Energy Producer Primary Secondary Tertiary

Consumer Consumer Consumer

Sun Grass Grasshopper Rat Owl

Fig. 2.6. Grazing food chain

2.6.2.2 Detritus Food Chain

Detritus food chain starts with dead and decayed
organic matter with the help of
(ike bacteria and fungi., etc.) and
then into detritus
feeding
micro-organisms
predators. This food chain 1s not directly dependent on solar organisms (detritivores) and their
energy.
2.6.3 Food Web
Food chains in ecosystem are no 1sO1ated linear chain
but are
interlocking pattern of food cnans KInOWn as to0d web. Food web interlinked with each other. An
is
Such as tronical forest and provides stability to the present in comnlex.
to move 'material and energy d t 1d
Seen as
ecosystem because it provides
eaong and being eaten
in a food many options
chain (Fio 2.7).
 Hawk

Snake

Fox Sparrow
Frog

Rabbit
Rat
Insect

Grass

2.7. Example of complex food web

Fig.
food chain and food web:
Importance of
nutrient cycle and energy flow in ecosystem.
1. Both maintain
the size of populations
chain maintains the ecological balance by maintaining
2. Food substances
biodegradable
of toxic non
also causes biological magnification
3. Food chain carnivore is much affected.
In such cases, top
like various pesticides.
Level
Concept of Trophic
consumers,
same position in a
food chain, as primary
that occupy the food chain,
Any class of organisms of the sequential stages in a
and tertiary Any
consumers.
consumers.
secondary consumers, in turn by primary, secondary, and
tertiary
at the bottom and trophic level.
occupied by producers sometimes considered to occupy
their own
are
Decomposers (detritivores) level to the next is called the
transferred from one trophic
is about 10 percent
The rate at which energy average of only
convert an
at each level convert
Since plants can only
Consumers
ecological efficiency. own organic
tissue.
chemical energy in their food to their at the lowest trophic
level
of the into chemical energy
1 percent of incident sunlight in incident sunlight that
reaches-
approximately of the energy
(the bottom of the food
chain), the percentage
consumer is about 0.0001.'
a tertiary
on 14/01/2016
tp://dictionary.reference.com/browse/trophic-level last visited
 Ecosystem 35

o7 THERMODYNAMICS PRINCIPLES & EcosYSTEM

2.7 THER

Energy is defined as the ability to do work. There are two laws of thermodynamics.
1. Ist Law of thermodynamics: Energy is neither creatcd nor destroyed but it can be
transfornmed from one form to another. Light energy for example can be transformed
into work, heat (solar energy), or potential energy of food (as green plants do) but none
of it is destroyed.
2. IInd Law of thermodynamics: No process involving an energy transformation WIll
unless there is degradation of concentrated form into
spontaneously occur energy from
a dispersed form. For example heat from the hot object tends
a
to become dispersed in
the cooler surrounding. It can also be stated as because some amount of energY 1s
always dispersed into unavailable heat energy, no spontaneous transformation of energy
into potential energy is 100% efficient.

2.8 ENERGY FLOW MODEL IN ECOSYSTEM

There are two model that explain the flow of energy in any ecosystem existing in bi0sphere.

2.8.1 Linear Energy Flow Model

The food chains are familiar to everyone in a sort of way because man himself occupies a

position at or near the end of the trophic level of the food chain. Example

Phytoplanktons Zooplanktons Small fish >Big fish Man

Man eats grains produced from green plants that fix the light energy (primary pfoducers).
He also eats beef of herbivores which feed on plants. Man
also occupies the intermediate
when his diet is composed of both plants
position between primary and secondary consumers
the primary consumers
and animal food. Since only a small part of sun energy is fixed by plants,
the length of the food chain.
that can be supported by a given primary production depend upon
available energy by one order (10) magnitude
Each trophic level in the food chain decreases the
(10 % Rule or Lindmann Principle).
of the two laws of thermodynamics can be
The principle of food chain and the working
the trophic level and the pipe depict the
clarified by energy flow diagram. The box represents
level. Energy inflow balances the energy
outflows as
energy flow in and out, of each trophic
transfer is accompanied by dispersion of energy
into
required by the First law and each energy
second law of thermodynamics.
unavailable heat energy (respiration) as required by
depicting three trophic level (box 1, 2 and 3)
Simplified energy flow diagram (figure 2.9)
in a linear food chain I-Total energy input A- total
assimilation|LA- Light absorbed by plants
P-Secondary productivity, NU-
PG- Gross primary Productivity. PN- Net primary productivity,
assimilated by consumer,'R- respiration.
Energy not used, NA- Energy not
 36 Basic Environmental Snudies

Producers Consumers
Trophic Levels 1 2
Green Plants Herbivores

NU NA Carnivores
Total Light

and La Pa or A PN A
P
T P

Heat R R

3000-15000- 15
L LA 0.3
PN
P
Source: Odum, E.P.
kcal/m/day
(1971)
Fig. 2.9. Linear energy flow model in the
The energy flow is Ecosystem
greatly reduced at successive trophic level from
to carnivores. Thus at each transfer of producers to herbivores
energy is lost in the form of heat energy from one trophic level
or any other form. There is
another, major part of
to
flow whether we consider it in term of successive reduction in the
total flow (I+A)
component. For e.g. when a total of 3000 Kcal of or secondary productivity and respiration
energy
absorbed (1500 KCal) and 1% is light falling upon green plants,
converted at first only 50% is
tends to be about 10% at trophic level (15KCal) Secondary
the carnivore's level due
successive consumer level.
Although productivity
to more efficient efficiency may
utilization
be upto 20% at
of food.
2.8.2 Y-shaped or Two Channel Energy Flow Model
In
Y-shapedenergy flow, grazing and detritus
food chain
practical than simple channel because are
sharply separated. It is more
i) It confirms to the
basic stratified structure of
() It separates the ecosystem.
grazing and detritus food chain (direct
utilization of dead
organic matter, respectively) in bothconsumption of living
time and space.
plants and
) Macroconsumer and microconsumers differ greatly in
In
Y-Shaped model (figure 2.10) size-metabolism relations.
one arm
detritus food chain. The two represent
arm
represent the the herbivore food
chain and the other
can influence arms differ
primary producers. For example, in marine fundamentally the way in which they
bay, the energy flow via grazing foou
 Ecosystem 37

is larger than via detritus food chain, whereas reverse is true for forest food chain where
t or more of net primary production is normally utilized in detritus food chain. Thus, in
90%
marine ecoOsystem
ecosystem the grazing food chain is the major pathway of energy flow and in the forest
ystem. the detritus food chain is more important.
In heavily grazed grassland, S0o or more of the net production may pass down the grazing
athway but many aquatic systems like shallow water operate as detritus system. Since all the
pathway but
ssimilated
not assi by the grazers, some is diverted to the detritus route. So the impact or
ood is
orazers on the communty aepends on the rate of removal of living plant and the amount of energy
that is assimilated.
in the food
Marine zooplanktons commonly graze more phytoplanktons than they can assimilate, the
excess being egested to the detritus food chain. Thus energy flow along different path is dependent
on the rate of removal of livng plant material by herbivores as well as on the rate of assimilation
on

in their bodies.

Detritus Predator

Grazing Food
Plants Chain

Sunlight

Detritus Food
Chain

Detritus Predator
Fig. 2.10. Y-Shaped energy flow model showing linkage between grazing
and detritus food chain.

2.9 CONTROLS/REGULATIONS ON ECOSYSTEM FUNCTION

The first one called as bottom-
There are two theories that explain the control of ecosystem.
controls ecosystems function.
up control, which states that nutrient supply to the primary producers
the increase in production of producers which
T the nutrient supply is increased, it results in levels will respond to the increased
propagated through the food web. Ali of the other trophic
will cycle faster).
alabtity of food (energy and materials
The second theory, called top-down control, states that predation on grazing animals, ultimately
number of predators, results in low population
ecosystem function. For example, increase in
OIS result in turn in more primary producers
erbivores, and that decrease in herbivores will
Thus, the regulation-of population numbers
d u s e Tewer of them are
being eaten by the grazers.
and overall productivity "eascades" from the top levels of the food chain to thne bottom level
i.e. the producers.

2.10 FOREST ECOSYSTEM

Forest ecosystem covers
nearly 40% of he land in the world. In India, it is estimated that
10% land area is only
occupied by the forest (Fig. 2.11). The different components of forest ecosystem
are as follows:

. Abiotic components: The abiotic conditions decide the type of forest ecosystem. The
torests present in the mountain region vary from that of plain
ike temperature, soil
region. Various abiotic conditions
types, pH and rainfall decide the type of vegetation in the forest which
further varies
along with latitude and altitude. The type of forest ecosystem is also decided
by variation in the soil texture. The dead
organic matter accumulates on the forest floor and
fulfills the requirements needed
by the plants after mineralization and also provides shelter
to the micro-organisms.
2. Biotic
components: The biotic component is
composed of large as well
plants and animals. These
as
microscopic
plants and animals are
unambiguous to each forest. For
coniferous trees are example,
specific to Himalayas and mangrove trees are specific to river
deltas and coastal
regions. In animals, snow leopards are found in the
the leopard and
tiger are found in other forests. The biotic Himalayas while
following categories: component is divided into
(a) Producers: They are of different
types in different stratification. In addition to
herbs and shrubs are also trees,
present in the ecosystem. The trees
deciduous forest 2re (Teak) Tectonica present in the tropical
grandis, (Sal) Shorea rubusta and (Dhak) Butea
frundosa. In temperate
conifer forest, the trees include Abies,
Rhododendron and Juniperus are present. (Chir) Pinus, Cedrus,

Fig. 2.11. Tropical Rain Forest

(b) (Rowa Wildlife
Consumers: They are categorized
into three
Sanctuary, Tripura)
) Primary
Consumers: They are types:
bugs, beetles and herbivores animals
mongoose,
spiders. The
fruit eat1ng larger animal includesincluding ants, flies, leafhoppers,
bats, flying foxes, deer, elephant,
etc. moles, shreWs.
 Ecosystem 39
i) Secondary ConsumerS: These are
birds. carnivore anim:als include snake, lizard, fox ana
i) Tertiary Consumers:
lion and tiger.
They occupy the top
position in the trophic level, for
exanipi
c Detritívores: These are
micro-organisms which decompose the dead
Itincludes fungus and
bacteria. The organic mate
Ganoderma, Trichoderma, Polyporus fungus species includes Aspergillus,
and Alternaria. Coprinus
bacteria includes Bacilus, Clostridium. The
The most common
species or
high in tropical region than
temperate
decomposition of dead organic matter S
high. It is because of the fact that region as the temperature of tropical region
climatic conditions. decomposition occurs 1s
very rapidly due to suitable

Fig. 2.12. Grassland Ecosyestem (Chattarpur,

Madhya Pradesh)
2.11 MOUNTAIN ECOSYSTEM
Mountains play a key role in providing forestfeeding perennial river systems, conserving
cover,
genetic diversity, and
providing an immense resource base for livelihoods through sustainable
tourism. At the same time, mountain ecosystem is
among the most fragile of ecosystems in
terms of susceptibility to
anthropogenic shocks. There has been significant adverse impact on
mountain ecosystems by way of deforestation, submergence of river
valleys, pollution of freshwater
sources, despoliation of landscapes, degradation of human habitat, loss of genetic
of
diversity. plantation
species not conducive to conservation of the mountain environment, retreat of glaciers, and
pollution.
The most significant proximate causes are illegal logging and commercial fuel wood collection,
esides faulty construction of infrastructure, unplanned urbanization and lack of enforcement of
uilding bye-laws, absence or disrepair of sanitation systems, setting up of polluting industries,
arge scale mining of low/unit value minerals, climate change, and excessive use of agricultural
Cnemicals are also prime cause of disturbances in Mountain ecosystem.
40 Basic Environmental Strudies
The
folowing measures need to be taken for conservation of mountain ecosystem:
(a Pronote, proteet and
conserve the forest by reforestation, afforestation and by declarin.
protected areas. ing
b)Adopt appropriate and place specific land planning (such Himalayan and Western
use
Ghat treated
differentially) tern
and watershed management practices for sustainable
development of mountain
ecosystems.
c)Adopt "best
practice" norms for infrastructure construction in mountain regions
or mnimze damage to sensitive to avojd
ecosystems and despoiling of landscapes.
(d Encourage cultivation of traditional varieties of crops and horticulture
by promotion of
organic farming. enabling farmers to realize a
price premium.
(e) Promote sustainable tourism
and access to
through adoption of "best practice" norms for tourism facilities
ecological resources, and multi-stakeholder partnerships to enable local
communities to gain better livelihoods, while
capacities of investors. leveraging financial, technical, and managerial
()Take measures to
regulate tourist inflows into mountain regions to ensure that these
remain within the
carrying capacity of the mountain ecology.
(g) Consider particular unique mountain
scopes as entities with "incomparable values", in
developing strategies for their protection.
2.12 GRASSLAND ECOSYSTEM
The grassland ecosystem roughly constitutes 19% of the earth surface. It has wide range of
vegetation mainly consist1ng of grasses and small annual plants (Fig. 2.12). The
ecosystem receives low rainfall and the soil depth grass land
as well as
the development of quality is poor. Therefore it restricts
a
large number of trees and shrubs, but is
grass cover. The different enough to hold the ofgrowth
components of the grassland ecos ystem
follows: are as
1. Abiotic: The elements like C,
H, 0, N, P and S are made
by CO, nitrate, phosphate, sulphate present in soil available to the organisms
2. Biotic: A range of grasses and herbs are
alongwith water available in ecosystem.
present. Several species of insects, birds and
mammals are these species evolved to
present,
The biotic
adapt to these
wide-open grass covered
areas. components can be seen under following forms in grassland
(a) Producers:Such type of ecosystem is ecosystem:
characterized by various
The main species includes grasses such species of grasses.
Brachiaria and Setaria.
as
Sporobolus, Dichanthium, Cyanodon,
(b) Consumers: The
importan consumers are
buffalo, deer and rabbit as well as other
organisms, insects, termite, millipedes, fox, snakes, frog and birds.
(c) Decomposer: Bacteria and ungi are the chief
decomposers. Fungus species includes
Aspergillus, Penicillium, Fusarium and Mucor. They decompose complex organic
matter into simpler
torm wnicn 18
agaim used by the plants to
produce biomass.
 2.13 DESERTE
ECOSYSTEM
It pies approximately
of ainfall per year. It 17% of Ecosystem 41
the land
water,
versity of
makes desert e of
carth. Desert
plants and
animals is veryanimals ecosystem less ecosystem
ccosystem
The arid and
and
semi-arid low
is
productive. receives
receives only 25-50
of the 25*>
over 10 region of India
and spreads
area and
spreads (lig. 2.13)
(Fig. 2.13). Because cm
scarcity
amals and winter
of mammals an states. covers The Indian desert 127.3 mha
of

on the natural
resourc migratory birds. (38.8%) of India's
fauna is
conservation
conservation base
necessitateHowever,
anservation ofof desert ecosystems, the
adoption
extremely
pressures of
geograpnica
geographical
rich in species
species diversity
diversiny
land degradation. The ecosystems. These rapidly a
n of increasing
different These innovativ
novative
ative and
pressures and g population
populationforfor
as follows:
components of the enhanced by integrated
are measures
measures
desert or arid and practices which
which lead
lead toto
1,
Producers:They form three semi-arid ecosystem are
dunes: These arecommunities:
(a) The Sand »

plants are less

(Jiwanti or
stable and
present
Croatalaria. Dodi,) in
minimum numbers.
The
grasses Leptadenia, (milkweed) Calotropis and Important
include Cenchrus,
(b) The Gravel (rattlepods)
the
ground. Community: It includes the plantsEragrostis
These with
and Pennisetum.
are
adapted stiff woody
gravels. The to
water areas low branches lying on

(c)
important plants are (Bindii) which have large
pebbles and
Rock
Community: The important communitiesTribulus, Aristida and Cleome.
Bukhar Jadi) of plants include
Lepidagathis and (Indigo) Indigofera. (Dudhi) Euphorbia.

Fig. 2.13. Dessert Ecosystem (Rajasthan)

.Consumers: The diversity of consumer is low as the conditions are not best suited for
C producers in comparison to other ecosystem. The most common consumers belong to reptiles
42 Basic Environmental Studies

and insects group and adapted to the dry conditions. During night, some nocturnal
nal .rodents and
birds are also found. ln mammals, camel is the most dominant species and also
known d wn as ship
of desert.
1. Decomposers: It includes bacteria and fungus which decompose tne scanty
dead oro
ecosuerganic
matter. The following measures need to be taken to conserve and manage desert
such as: ystem,
(a) Intensive water and moisture conservation through practices based on
traditional (Joha
had
rejuvenation) and science based knowledge, and relying on traditional
infrastructr
6)
cture.
Enhancing and expanding green cover based on local species.
(c) Reviewing the agronomic practices in these areas, and promoting
and varieties, which
agricultural practices
are well adapted to the desert ecosystem.
2.14 THE POND ECOSYSTEM
India's freshwater resources comprise the
single most important class of natural
endowments
enabling its economy and its human settlement
river systems, patterns. The freshwater resources comprise the
groundwater, and wetlands. Each of these has a
unique role, and
linkages to other environmental entities. characteristic
It is the
simplest. aquatic ecosystem which is self sufficient and self
Generally small
ponds dry during summer seasons and regulating in nature.
2.14). Pond ecosystems have recovers again during monsoon (Fig.
following components:
(a) Abiotic Components: The minerals like
N, Ca, 02, CO2 are dissolved
constitute the abiotic components. The other in water that
factors like heat,
important for pond ecosystem. temperature, pH are also

Fig. 2.14. Pond ecosystem in an Indian village. (Beel in Kailashahar, Unakoti, ripura)
 Ecosystem 43

and minerals
photosynthetic bacteria use light
(b) Biotic:

and
plants. phytolanktons
The Sagittaria,
mportant plant species are Typha,
P r o d u c e r s : "

1. process. The
start the photosynthetic
Utricularia Vallisneria, Eichhornia,
and Salvinia. The important
drilla. Azolla. and Closterium.
includes Pandorina, Volvox, Zygnema
algal species mites, crustaceans and
ludes mainly the fishes, insect larvac, beetles,
It includ by the large
The top trophic level is occupied
Consumer:

2. rotifers are zooplanktons.

mollusks. The phytoplanktons and
small fishes.
on both
which feed organic
fishes role in decomposing the
A number of microbes play important bacteria.
Decomposer: actinomycetes and
It includes chiefly fungus,
matter in the ponds.

National Park,
Headed Geese in Kaziranga
Buffalo and Bar
ecosystem (Wild
2.15. Wetland Assam)
Fig.

Restoration: A Success Story

Lagoon
Ecosystem forms the base of
Chilika Odisha in India,
State of
situated in the and around the
water lagoon, farmers living in
Chilika brackish fishers and 400,000
than 200,000 catchments choked
the connection
livelihood security
of m o r e degraded
catchments.
Siltation from
fisheries (from 8,000 mt to
decline in
wetland and its adjoining to a rapid shrinkage of
leading there was
the Bay of Bengal weeds and
consequently
of lagoon with invasive especially
proliferation of livelihoods of communities,
less than 1,000 mt) tremendous impact on the culture also led to
volume. This had a Introduction of shrimp
the area and sustenance.
were to restore
on the lake for of the
intervention

Tishers who depended The objectives the livelihoods

of the lake. and securing
pressures on the ecology its biodiversity
by restoring
approach
with an ecosystem
Cnilka
communities.
of the dependent
 mental Studies

Chilika Development
Authority was constituted in 1991 to implement an
programme such as watershed ecological restos
management,
education and outreach. After these
fisheries development, ecotourism
develo restoration
the lake
efforts following positive changes have
system, reappearance of 6 species of fish-in addition, 43 taken niapment
2 Indian fish, 4
spiny lobster species, Decrease in area under the freshwater weed prawn, 7 crab and
(water hyacinth), Expansion of Eichhornia crass
seagrass meadows and species diversity. Increase in
and habitat of
Irrawaddy dolphin from 70 in 2003 to 152 in 2013. populatie
tion
of the Building on the recove
ecosystem, the lake fisheries have revived significantly-the annual
1747 million tonnes in 2000 to very
catch grew from
also
14,228 million tonnes in 2012. The tourist inflow to om
increased substantially, from 200,000 visitors during 1994-2000 to Chilika has
2008.3 430,000 during 2000
2.15 Wetlands
Wetlands, freshwater or brackish,
to provide numerous ecological services. They
aquatic flora and fauna, as well as numerous provide habitat
The density of birr'3, in species of birds, including migratory
particular, is an accurate indication of the ecological health of a species
wetland. Several wetlands have
sufficiently unique ecological characteristic and have been particular
internationally as Ramsar Sites under Ramsar Convention recognized
services such as freshwater for (1971) (Fig. 2.15). Wetlands provide
agriculture, animal
husbandry, and domestic use, drainage services
provide livelihoods to fisherfolk, sustainable tourism
and recreation.

Fig. 2.16. Chilika Lake & Local

Fisherman
3,
http:/ www.chilika.com/coastal_zone_project.ntm, np:/www.Iczmpodisha.org/last visited
2016
on 15/0/
 Ecosystem 45
ands are now
Wetland getuing threatened because of
dumping offsolid
soi and hazardous waste, introduction of some alien species of tlora,
filling for use of land for
and reclamation for agricultural
of houses and development or construction
purpose to mect
the growing
octting shrinked and severely polluted,
ant
population need. Thus,
causing
wetkands

ater level and

ground water
biodiversity loss) and health adverse environmental (flood, decreasing
sary, which looks at each
wetlands is necess;
impacts on human beings. A holistic view
of
identified
needs, and its own wetland terms of its causal linkages
er natural entities. human
in
with
attributes.
2.15.1 Wetle Wetland Status in India & Conservation
is bestowed with a rich
Strategy
a
diversity wetlands, ranging from
of
high altitude lakes of the
alaas, floodplains and marshes
of the Gangetic Bramhaputra
Green Indian Desert to extensive
alluvial plains, saline flats
of mangroves marshes bordering the country's East and West
astline. As per remote sensing imagery based
assessment India has total of 757,060 wetlands
ering a total area of ca. 15.26 million ha, roughly
equal to 4.6% of its land area (2006-07).
Of this, inlands wetland constitute 69.22%
(10.56 million ha). There are 0.556 million wetlands
with area less than 2.25 ha.

India is a signatory
Ramsar Convention and is committed to
to
wise use' of all wetlands
in her territory. As on date, 26 sites have been
designated as Wetlands of International importance
under the Convention. Conservation of wetlands is one of the
high priority areas of MoEFCC.
The Ministry has been providing financial support to State Governments for
implementing action
plan for conserving wetlands under the National Wetland Conservation
Programme (NWCP)
since 1986. In 2001, National Lake Conservation Plan (NLCP) was introduced to address
pollution
issues in urban and semi-urban environment through interception,
diversion and/or treatment of
pollution load entering the lake.
As December 2012, nearly 150 priority sites have been prioritized for conservation and
on

management under the two schemes. In February 2013, the Ministry has since launched the
National Programme on Conservation of Aquatic Ecosystem (NPCAE) for conservation of both
lakes and wetlands with a significant increase in allocation of resources.
 46 Basic Environmental Studies

1367 out of 3513 wetlands in Assam are under severe threat due to invasion of vario
urious
alien aquatic weeds (Water Hyacinth).

2.15 SUcCESSION
Succession can be defined as the appearance in an orderly sequence or different
communiti.
over a period of time in the given area. Community is an assemblage ot interacting populatior
Occupying a given area.
It
begins with the small pioneer species entering the new area and paving the way f
bigger and complex varieties of species. The various intermediate stages in the process ofpla
Succession are called "seral communities" and each
community is called "Climax".
stage is called a seral stage. The fina
2.15.1 Types of Succession
On the basis of source of
energy and nutrition, interaction/colonization, succession can be divided
into three different types:

A. On the basis of Source of

Energy and Nutrition
i) Autotrophic succession: In autotrophic
succession, rate of production is always more
than the rate of
respiration. Initially primary producers are present in
of production is more than majority and rate
of production and
respiration but later biomass of
organism increase and ratio
respiration become one. The diversity of species increases with
in organic matter and available increase
energy. The biomass also increases in the
climax community.
i) Heterotrophic succession: The ratio of
the initial of
respiration is greater than production during
phase heterotrophic succession. The numbers of
more in the early development. Such type of succession starts heterotrophic
in the area
animals are
in the organic
matter. For example, small areas of
which is rich
rivers and streams
large amount of sewage or leaf litter. which receives
B. On the basis of Colonization:
ii) Primary succession:
Primary succession occurs in the area where
occupied irst tume by the few environmental conditions
are elementary and that area is
This type of succession is called
primary succession. It simple living organisms.
harren area, like rocks, which were not always starts in an
an uninhabited,
initiany oCcupied by
the conditions of the area were not Iavourable any type of
tor the
existence community and
of anv life
Secondary uccession: Secondary succeSsIOn ocCurs m
the area
Occupied by some types of community. I ne which was previously
has been arca wmCn1s under
devastated by some natural or human influenced the process of colonization
cold
deforestation, excessive grazing or abrupt cnanges in the activities like
burning
climatic conditiona of forests,
 Ecosystem 47
vears, that area is
again oCcupied
Succession. The process of secondary bysuccession
some new
is
community. It is called secondary
succession as the area already had enough always much higher than the
nutrients and primary
other favourable factors, contributed
by previously occupied
community which speed up or
accelerates the succession process.
C. On the basis of lnteraction:

(V) Autogenic succession: In mOst of the

cases, the
the process of
early succession in the given community which is formed during
area, react itself with the
thus modifies the environment and current environment
results in the
some new modified community. Such
replacement of its own community by
succession is called
(vi) Allogenic succession: In some autogenic succession.
cases, one
due to some other forces than the community is replaced by another community
effects of
called allogenic succession and it may occur incommunities on the environment. This is
ponds where the nutrients and other
a
highly disturbed or eroded area or in
and in turn the communities.
pollutants enter from outside and modify the environment

2.15.2 Kind of Succession

The succession can be broadly classified into two
habitat.
major kinds depending on the nature of the

(A) Xerosere Succession

(B) Hydrosere Succession

(A)Xerosere
Xerosere succession occurs in dry conditions like bare rocks (Fig. 2.16) sand dunes and salt
deserts.
Stages of Xerosere: It involves
following stages:
1. Crustose Lichen stage: It starts in the bare rock where
life existed previously. The
no
rocks arelarge and solid that
provides no space for the rooted trees to grow. The first
stage, that gets established in the area is called pioneer stage. It includes
lichens such as, Rhizocarpon, Rhinodina, and Licanora. They have web of
species of
root like
structure that adhere to the surface of the rock and help to absorb the moisture
from
the
surrounding environment. The propagules of these lichens reach to the area through
air. These lichen
species produce acids which corrode the rock that help in genesis of
SOil. They trap and collect soil
particles from the wind which also contributes in the soil
formation. When they die, their thalli decompose to form humus and get mixed with the
ncipient soil. Dead material also makes the environment unfit for the growth of other
existing crustose lichens but make it fit for the growth of foliose lichens.
 Hock Herbs Shrubs Wooden trees Cimax
Fig. 2.16.Diagram showing the various stages of Xerosere succession
2. Foliose Lichen Stage: It is the second
stage of succession in which foliage lichens like
Dermatocarpon and Parmelia grow gradually due to the slow process of soil formation
These leafy lichens do not allow
sunlight to reach the crustose lichen which causes the
death of these lichens. The foliose lichens
accumulate more soil particles and water
from air and help to form soil. The dead remain of these foliose lichens
decompose to
form humus which mixes with soil
particles and help in building the substratum and
improving the soil moisture contents.
3. Moss Stage: As result of death of crustose and
a
foliage lichens, more formation of
soil takes place and humus is formed from the dead and decomposed lichens which
further increases the fertility of the soil. At-this stage mosses like Grimmia, Tortula and
Polytrichum start growing. The mosses now establish them over foliose lichen. Soil
formation continues from dust, and dead and decomposed bodies of mosses. Water content
of soil increases further due to thick layer of soil that facilitates growing of herbs.
4. Herbaceous Stage: Due to increase in the content of humus and mineral salt in the
soil, the annual herbs start growing in the area. Later, the biennial and perennial plants
also grow. Among the plants, Aristeda, Leucas, Euphorbia and Cynodon are the most
common species.
5. Shrub Stage: At this stage, quality and quantity of humus and soil moisture is further
increased. The soil living.bacteria and fungi grow further. Different types of shrub like
Rhus, Phytocarypus, Cassia, Solanum and Croton begin to grow. The shrubs modify
the habitat and the dead parts of the lea ves, stems and roots of these shrubs mpo se
to enrich the soil by humus. The water holding capacity of the soil increases further due
to shading of the soil by these dense shrubs. The increased humidity favours the growth

of the seedlings of the tree.

The succession terminates in a climax community ia

7. Forest Stage or climax Stage: to the establisha
tree stages which develop prior
the forest. There are many intermediate climatic conditions,
forest type depends upon
of a climax community. The
 gets
( B ) H y d r o s e r e

Hydrarch succession o c u r s in a pond and its Initial aquatic community finally

or or funning.
munity (Fig. 2.17). The water may be stagnant
medium
drosere
terTestrial
converte
into a follows.
are as

hvdrosere
consists of hydrophytic specics. The various distinct ages
dominated
is
The
stage: The depth of pond or lak is ore than 10 fcct which
Submerged Elodea,
1. certain macrOscopic algac like Najas, Vallisneria,
Besides
phytoplanktons.
by amoeba,
Hyd irilla and Utricularia occupy the water body. In animals,
Ceratophyllum, insect larvae,
and Euglena are commonly found. Other animals include
aramecium sink
and Daphima. The remams qf these organisms due to death and decay
Cvclops streams are
bottom which fornis the humus, The eroded soil particles brought by
to the
of the pond.
in dead nass of vegetation that gradually decreases the depth
deposited T he new
the pond becomes less suitable for the submerged vegetation.
As a result.
the older plants and provides space to the new vegetation.
habitat replaces
Woodland Stage Marsh Meadow Stage
Reed Swamp Stage

omearged atage Floating Stage

of Hydrosere succession.
Fig. 2.17. Lake showing the various stages
Arun Kumar Maurya)
(Khajiar Lake, Himachal Pradesh; Image: Dr
2. Floating Stage: The depth of water further decreases to 6-8 feet. The floating plats
Monochoria and
Nymphaea, Nelumbo, Trapa, Aponogeton,
'

like Castalia,
Limnanthemum make their appearance. These are all rooted hydrophytes with large
animals are
leaves. The inhabiting gill breathing snails, frogs, diving beetles, turtles
Hydra,
and snakes. The depth of pond further decreases due the soil building process and the
pond is invaded by swamp plants.
3. Reed Swamp stage: amphibious stage. The depth of pond further
It is also known as

decreases to 1-4 feet. The vegetation is represented by Typha,

Carex, Pontideria,
have much branched rhizomes
Mariscus, Sagittaria and Scirpus. The reed swamp plants
and constitute dense vegetation. During reed swamp stage, floating animals are replaced

by dragon flies, lung breathing snails, water scorpion and scavenger beetles. The bottom
Is inhabited by annelids. The water depth further decreases and provides habitat to the
 Basic Environmental Studies

next stage.

4. Marsh Meadow Stage: The reed swamp community disappears due to decrease in the
depth of water level and increasing amount of light in the pond. The plants like Juncus
Cyperus and Carex invades the area. They have tough rhizomes with slender and copious
roots. In animals, Psidium and Annodonta are commonly found. At the end ot the
stage. the soil become devoid of water content and depends upon the rainfall for its
water requirement..

5. Woodland Stage: The wood land stage consists of shrubs and trees. Shrubs like Cornus,
Salix and Cephalanthus and tree like Populus and Alnus occupy the region. In the
woodland stage, terrestrial forms of animals invade the area. The Plants react with the
environment by producing shades and by decreasing the water table due to transpiration
and provide conditions for the higher stages of community.
6. Climax Stage: The dead and decaying part of wood land plants causes the accumulation
of the humus. As a result humid soil is enriched with bacteria, fungus and other micro
organisms. The soil is further enriched with organic matter. During succession, the change
in species composition and number and kind of autotrophs and heterotrophs occur. In
the Tropical climax community, a tropical rain forest develops while in the temperate
region mixed forest of Acer Ulmus and Quercus develop.

QUESTIONS
Define Ecosystem?
Define biotic and abiotic components of the environment?
Differentiate between food chain and food web?
Discuss pond as an example of ecosystem?
Describe the process of energy flow in an ecosystem?

What are the biotic factors of ecosystem?

What is the difference between autotrophs and heterotrophs?
What is decomposer?
Give an example of grazing food chain?
What do you understand by succession?

Mention three characteristics of succession?

sre-TIANC-