Module-II

ECOSYSTEM
The interaction and interrelationship between the living community (plants, animals, and
organisms) in relation to each other and the non-living community (soil, air, and water) is
referred to as an ecosystem. Thus, an ecosystem is a structural and functional unit of
biosphere. It is made up of living and non-living beings and their physical environment.
The term ecosystem was first proposed by A.G.Tansley (1935) who defined ecosystem
as follows: “Ecosystem is defined as a self-sustained community of plants and animals
existing in its own environment.”
“Odum (1971) defined ecosystem as any unit that includes all the organisms in a given
area interacting with the physical environment, so that a flow of energy give rise to a
clearly defined trophic structure, biotic diversity and material cycles within the system”.
“Michael(1983) defined ecosystem as a community of interdependent organisms
together with the environment”.
CONCEPT OF ECOSYSTEM:
In an ecosystem, the interaction of life with its environment takes place at many levels.
A single bacteria in the soil interacts with water, air around it within a small space while
a fish in a river interacts with water and other animals. Considering the operational point
of view; the biotic and abiotic components of an ecosystem are so interlinked such that
their separation from each other is practically difficult. So, in an ecosystem both
organisms (biotic communities) and abiotic environment (rainfall, temperature, humidity)
each influence the properties with other for maintenance of life.
Types of Ecosystems: Ecosystem may be natural or artificial.
1. Artificial Ecosystem: These are maintained or created artificially by man. The
man tries to control biotic community as well as physico chemical environment.
Eg: Artificial pond, urban area development, zoo etc.
2. Natural Ecosystem: It consists of Terrestrial and Aquatic Ecosystems which are
maintained naturally.
a) Terrestrial Ecosystem: This ecosystem relates to biotic components living on the
land. Vegetation dominates the community and the types of vegetation affect the
climate, soil structure & a rapid exchange of O 2, water & CO2.
b) Aquatic Ecosystem: This ecosystem relates to biotic community living in water.
The types of water (fresh water, saline water, polluted water) dominate and affect
the pH of water, depth of water, temperature of water etc. Aquatic ecosystem has
been sub-divided into fresh water and saline water based on the quality of
water.
STRUCTURE OF ECOSYSTEM:
Generally ecosystems consist of two basic components.
1.Abiotic component.
2.Biotic component.
Non Living Components (Abiotic)- Non living components are the physical and
chemical factors that directly or indirectly affect the living components e.g. air, water,
land, rock etc. Non-living components are also called Abiotic components. Physical
factors include sunlight, water, fire, soil, air, temperature etc.
Chemical factors include salinity of water, soil nutrients, oxygen dissolved in water etc.
Living Components (Biotic)-Living components in an ecosystem are either producers
or consumers. They are also called biotic components. Producers can produce organic
components e.g. plants can produce starch, carbohydrates, cellulose from a process
called photosynthesis. Consumers are the components that are dependent on producers
for their food e.g. human beings and animals.
Biotic Components are further classified into 3 main groups
1. Producers 2. Consumers 3.Decomposers or Reducers
1. Producer (Autotrophs): The green plants have chlorophyll with the help of which
they trap solar energy and change it into chemical energy of carbohydrates using simple
inorganic compound namely, water and carbon dioxide. This process is known as
photosynthesis. The chemical energy stored by the producers is utilized partly by the
producers for their own growth and survival and the remaining is stored in the plants for
their future use. They are classified into two categories based on their source of food.
a) Photoautotrophs: An organism capable of synthesizing its own food from inorganic
substances using light as an energy source. Green plants and photosynthetic bacteria
are photoautotrophs.
b) Chemotrophs: Organisms that obtain their energy through inorganic molecules such
as iron and magnesium. Ex-Bacteria and fungi etc.
2. Consumers (Heterotrophs): The animals lack chlorophyll and are unable to
synthesis their own food therefore they depend on the producers for their food. •They
are known as heterotrophs (i.e. heteros= others, trophs= feeder).The Consumers are of
4 types:
(a) Primary Consumer: (Herbivores) i.e. Animal feeding on plants, e.g. Rabbit, deer,
goat etc.
(b) Secondary Consumers: The animal feeding on Herbivores are called as secondary
Consumer or primary carnivores. Ex: Cats, foxes, snakes, Dogs etc.
(c) Tertiary Consumers: These are large carnivores which feed on secondary
consumers. Ex: Wolves, Sharks, Whales, turtles etc.
(d) Quaternary Consumers: They are also called omnivores these are largest
carnivores which feed on tertiary consumers and are not eaten up by
any other animals. Ex: lion and Tiger etc.
3. Decomposers or Detrivores: Bacteria & fungi belong to this category. They break
down the dead organic matter of producers & consumers for their food and release to
the environment the simple inorganic and organic substance. These simple substances
are reused by the producers resulting in a cyclic exchange of material between biotic &
abiotic environment.
Eg: Bacteria, Earth worms etc.
Functions of the Ecosystem:
The functions of the ecosystem are as follows:
 It regulates the essential ecological processes, supports life systems and renders
stability.
 It is also responsible for the cycling of nutrients between biotic and abiotic
components.
 It maintains a balance among the various trophic levels in the ecosystem.
Food Chain: The transfer of food energy from the producers (plants) through a series of
organisms (Herbivores, Carnivores) successively with the repeated activities of eating
and being eaten is known as food chain. In an ecosystem(s), one organism is eaten by
the second who in turn is eaten by the third and so on... This kind of feeding relationship
is called food chain. Examples of food chain:
1. Grass→ Grasshopper→ Frog→ Snake→ Hawk.
2. Grass→ Mouse→ Snake →Hawk.
3. Grass→ Rabbit→ Man.
4. Grass→ Mouse→ Hawk.
5. Plant leaf →Caterpillar →Sparrow →Hawk.
Explanation: A caterpillar eats a plant leaf, a sparrow eats the caterpillar, and a hawk
eats the sparrow. When they all die, they are all consumed by micro organisms like
bacteria (or) fungi which break down the organic matter and convert it into simple
inorganic substances that can again be used by the plants. In nature, there are two basic
types of food chains: 1. Grazing food chain and (2) Detritus food chain
1. Grazing food chain: This food chain starts with green plants (primary producers)
and goes to herbivores and on to carnivores.
 Ex: 1. Grass → Grasshopper → Frog → Hawk.
 2. Grass → Grasshopper → Rat → Fox.
 3. Grass → Rabbit → Fox.
 4. Grass → Rat → Snake →Hawk.
2. Detritus food chain: This food chain starts from dead organic matter (dead leaves/
plants / animals) and goes to Herbivores and on to Carnivores and so on.
Ex:1. Leaves or dead plants→ Soil mites→ Insects→ Birds.
2. Dead organic matter→ Bacteria → Insects.
3. Dead leaves → Algae→ Fish→ Man.
FOOD WEB: Food web is a net work of food chains where different types of organisms
are connected at different trophic levels so that there are a number of options of eating
and being eaten at each trophic level. (A trophic level refers to an organism‘s position in
the food chain).
1. Grass→ Grasshopper→ Hawk
2. Grass→ Grasshopper→ Lizard→ Hawk
3. Grass→ Rabbit→ Hawk
4. Grass→ Mouse→ Hawk
5. Grass→ Mouse→ Snake→ Hawk
Differences between food chain and food web

ECOLOGICAL PYRAMIDS:
Graphical representation of the trophic levels is called as Ecological Pyramids. It was
devised by an ecologist “Charles Elton” therefore this pyramid are also called
Ecological pyramid or Eltonian pyramids.
Types of Ecological Pyramids:
They are:
1. The pyramid of Numbers (showing population).
2. The pyramid of Biomass (showing total mass of organisms).
3. The pyramid of energy (showing energy flow).
Hence, all producers (micro & macro plants) belong to the I trophic level; all primary
consumers belong to II trophic level and organisms feeding on these consumers belong
to the III trophic level and so on.

1. The pyramid of Number: It shows the relationships among the producers,

herbivores and carnivores at successive trophic levels in terms of their number. Mostly
the pyramid of number is straight (or) upright with number of individuals in successive
higher trophic levels goes on decreasing from base to apex. The maximum number of
individuals occurs at the producers‘level. They support a small number of herbivores.
The herbivores, in turn, support a fewer number of primary carnivores and so on….. Top
carnivores are very few in number. For Example:
(1) In a grass land ecosystem: Grass→ Grasshoppers→ Frogs→ Snakes→ Peacock / Hawk.
(2) In a pond ecosystem: Phytoplankton→ Zooplankton→ Fish→ Crane
The pyramids may be inverted in a few cases: A single plant may support the growth of
many herbivores and each herbivore in turn provides nutrition to several parasites which
support many hyper-parasites. Thus, from the producer towards consumers, there is a
reverse position i.e., the number of organisms gradually shows an increase making the
pyramid inverted in shape.
(3) In a Forest ecosystem: Tree→ Birds / deer →Parasites→ hyper parasites Tree→ Birds→
eagle

2.The Pyramid of Biomass: The amount of organic matter present in environment is

called biomass. In pyramids of biomass, the relationship between different trophic levels
is mentioned in terms of weight of organisms. The pyramid may be upright for grassland
ecosystem and inverted for pond ecosystem. Example: Vegetation produces a biomass
of 1000 kg. Out of this 100 kgs of biomass for herbivores, which in turn only 10 kg of
biomass for primary carnivores that gives rise 1 kg of biomass for second order
carnivores and so on…
1000 100 kgs 10 kgs 1 kg
kgs

Vegetati Herbivor primary Second

on es carnivor ary
es carnivor
es

Hence, a vegetarian diet can support a larger population than a Non – vegetation diet.

3. The pyramid of energy: The amount of energy trapped per unit time and area at
different trophic levels of a food chain with producers forming the base and the top
carnivores at the apex is called pyramid of energy. The energy content is generally
expressed as K cal /m2 / year or KJ / m2 / year.
Large Fish ---126 KJ / m2 / year Small Fish ----840 – 126 KJ / m2 / year Zooplankton ----
7980 KJ / m2 / year Phytoplankton (producers) --- 31080 KJ / m2 / year
Energy flow /Transformation of energy in Ecosystem
The chemical energy of food is the main source of energy required by all living
organisms. This energy is transmitted to different trophic levels along the food chain.
This energy flow is based on two different laws of thermodynamics:
First law of thermodynamics, that states that energy can neither be created nor
destroyed, it can only change from one form to another. Second law of
thermodynamics, that states that as energy is transferred more and more of it is
wasted. The energy flow in the ecosystem is one of the major factors that support the
survival of such a great number of organisms. For almost all organisms on earth, the
primary source of energy is solar energy. It is amusing to find that we receive less than
50 per cent of the sun’s effective radiation on earth. When we say effective radiation, we
mean the radiation which can be used by plants to carry out photosynthesis. Most of the
sun’s radiation that falls on the earth is usually reflected back into space by the earth’s
atmosphere. This effective radiation is termed as the Photosynthetically Active
Radiation (PAR). Overall we receive about 40 to 50 percent of the energy having
Photosynthetically Active Radiation and only around 2-10 percent of it is used by plants
for the process of photosynthesis. Thus, this percent of PAR supports the entire world as
plants are the producers in the ecosystem and all the other organisms are either directly
or indirectly dependent on them for their survival.
The energy flow takes place via food chain and food web. During the process of energy
flow in the ecosystem, plants being the producers absorb sunlight with the help of the
chloroplasts a part of it is transformed into chemical energy n in the process of
photosynthesis. This energy is stored in various organic products in the plants and
passed on to the primary consumers in the food chain when the herbivores consume
(primary consumers) the plants as
food and convert chemical energy accumulated in plant products into kinetic energy,
degradation of energy will occur through its conversion into heat.
Then followed by the secondary consumers. When these herbivores are consumed by
carnivores of the first order (secondary consumers) further degradation will occur.
Finally, when tertiary consumers consume the carnivores, again energy will be degraded.
Thus, the energy flow is unidirectional in nature.
Based on the source of their nutrition or food, organisms occupy a specific place in the
food chain that is known as their trophic level. Producers belong to the first trophic
level, herbivores (primary consumer) to the second and carnivores (secondary
consumer) to the third.(Fig.)

The important point to note is that the amount of energy decreases at successive trophic
levels. When any organism dies it is converted to detritus or dead biomass that serves as
an energy source for decomposers. Organisms at each trophic level depend on those at
the lower trophic level for their energy demands.
Moreover, in a food chain, the energy flow follows the 10 percent law. According to this
law, only 10 percent of energy is transferred from one trophic level to the other; rest is
lost into the atmosphere.
ECOLOGICAL SUCCESSION:
Ecological Succession is the phenomenon or process by which a community
progressively transforms itself until a stable community is formed. It is a fundamental
concept in ecology, refers to more or less predictable and orderly changes in the
composition or structure of an ecological community. Succession may be initiated either
by formation of new, unoccupied habitat (e.g. a lava flow or a severe landslide) or by
some form of disturbance (e.g. fire, severe wind throw, logging) of an existing
community. Succession that begins in areas where no soil is initially present is called
primary succession; whereas succession that begins in areas where soil is already
present is called secondary succession.
Clement's theory of succession/Mechanisms of succession
F.E. Clement (1916) developed a descriptive theory of succession and advanced it as a
general ecological concept. His theory of succession had a powerful influence on
ecological thought. Clement's concept is usually termed classical ecological theory.
According to Clement, succession is a process involving several phases:
1. Nudation: Succession begins with the development of a bare site, called Nudation
(disturbance).
2. Migration: It refers to arrival of propagules (a vegetative structure that can become
detached from a plant and give rise to a new plant, e.g. a bud, structure (such as a
cutting, a seed, ) that propagates a plant.
3. Ecesis: It involves establishment and initial growth of vegetation.
4. Competition: As vegetation became well established, grew, and spread, various
species began to compete for space, light and nutrients. This phase is called
competition.
5. Reaction: During this phase replacement of one plant community by another occurs.
6. Stabilization: Reaction phase leads to development of a climax community.
Seral communities:
A seral community is an intermediate stage found in an ecosystem advancing towards its
climax community. In many cases more than one seral stage evolves until climax
conditions are attained.
Hydrosere : Community in freshwater
Lithosere : Community on rock
Xerosere : Community in dry area
Halosere : Community in saline body (e.g. a marsh)
Climax community:The final or stable community in a sere is the climax community or
climatic
Types of Ecosystem:
There are two main ecosystems:
1.Terrestrial Ecosystems: Terrestrial ecosystems are classified into various types
based on temperature and annual rainfall. A few examples of terrestrial ecosystems
are listed below:
a. Grassland Ecosystems
b. Forest Ecosystems
c. Desert Ecosystems
2.Aquatic Ecosystems:Aquatic ecosystems are majorly two types:
a. Freshwater Ecosystems
b. Marine/Saltwater Ecosystems
1. Forest Ecosystem:
A forest ecosystem is an ecosystem of forests and resources. Forests are renewable
natural resources. Forests are formed by a group of plants that are structurally
defined by their trees, shrubs, herbs, climbers, and ground cover. Soil, animals,
insects, microorganisms, and birds are the most important interacting units of a forest
ecosystem.
1. Abiotic Components of the forest include inorganic and organic components
present in the soil along with temperature, rainfall, light, etc.
2. Biotic Components are represented by producers, consumers, and decomposers.
Types of Forest Ecosystems
There are a few types of forest ecosystems listed below:
1. Tropical Evergreen Rainforest: Only a small percentage of tropical forests are
rainforests where average rainfall is 80-400 inches in a year. This forest is
characterised by deep and dense vegetation consisting of tall trees reaching
different levels.
2. Tropical Deciduous Rainforest:The main characteristic of tropical deciduous
rainforest are broad-leaved trees along with dense bushes, shrubs, etc. Two main
seasons – summer and winter – are distinctly visible there. This type of forest is
found in many parts of the world. A large variety of flora and fauna are found here.
3. Temperate Evergreen Forest:Temperate evergreen forest is a type of forest
that is characterised by a smaller number of trees but an adequate number of ferns
and mosses.
4. Temperate Deciduous Forest: Temperate deciduous forest evolves in the moist
temperate region with sufficient rainfall. Here also, winter and summer are well
defined, and trees shed their leaves during winter. Dominant trees are maple, oak,
peach, etc.
5. Taiga/Boreal:Situated just south of the Tundra, Taiga is characterised by
evergreen conifers. The average temperature is below the freezing point for almost
half of the year.

Components of Forest Ecosystem

1.Producers:Producers can synthesis their own food by the photosynthesis process.
All green plants are considered producers of the ecosystem as they convert sunlight
into the chemical energy of food.
2.Primary Consumers: Since the consumers can not prepare their own food, they
depend on producers. Herbivorous animals get their food by eating the producers
(plants) directly. Examples of primary consumers are grasshoppers, deer etc.
3.Secondary Consumers: Secondary consumers draw their food from primary
consumers.
4.Decomposers: The decomposers of the forest ecosystem break down dead plants
and animals, returning the nutrients to the soil so that they can be used by the
producers. Apart from bacteria, ants and termites are important decomposers in the
Amazon rainforest. Millipedes and earthworms also help to break down dead matter.
5.Nutrient Cycle: The nutrient cycle is cyclic. For the proper functioning of
ecosystems, nutrients are required. Carbon, hydrogen, oxygen, and nitrogen
constitute about 95%of the mass of living organisms.
6.Energy Flow: In a forest ecosystem, the grass, which draws its nutrition from sun,
soil and water, is eaten by the grasshopper, which in turn is eaten by frogs, snakes,
and vultures in succession (different trophic levels). In this process of eating and
being eaten, nutrients are passed from one step to the next in a food chain. The flow
of energy that occurs along a food chain is called energy flow. The pyramid of energy
represents the total quantity of energy at each trophic level of a food chain. The flow
of energy is always unidirectional.
Characteristics of Forest Ecosystem
1. Warm temperatures and sufficient rainfall are characteristics of forests, resulting in
the formation of numerous ponds, lakes etc.
2. The forest maintains climate and rainfall.
3. The forest supports many wild animals and protects biodiversity.
4. The soil is rich in organic matter and nutrients, which support the growth of trees.
Functions of Forest Ecosystem
1.Goods Obtained from Forests:There are various types of food products such as
honey, wild meat, fruits, mushrooms, palm oil and wine, and medicinal plants
obtained from forests. Other than edible parts, we can obtain timber, wood biomass,
cork, etc. from forests. The fuel can be extracted from old trees that are buried under
the soil.
2.Ecological Functions:Forests play an important role in maintaining ecological
factors such as climate, carbon storage, nutrient cycling, and rainfall.
3.Culture and Social Benefits:The tribal people who live in the forests treat forests
as nature goddesses. The traditional beliefs and spirituality save wild animals from
hunters and cutting down of trees by urban people. A few modern people visit forests
for recreation.
2.GRASSLAND ECOSYSTEM: Dominated by grass –few shrubs and trees are also found
– rainfall average but erratic (unpredictable); – overgrazing leads to desertification.

Three types – depending on the climate

1. Tropical grass lands – found near the boarders of tropical rain forests. Eg. Savannas
in Africa. Animals– Zebra, giraffes etc. – fires are common in dry seasons – high in
photosynthesis – deliberate burning leads to release of high CO 2 – global warming.
2. Temperate grasslands – flat and gentle slopes of hills. Very cold winter and very
hot summer - dry summer fires do not allow shrubs and trees to grow – soil is quite
fertile – cleaned for agriculture.
3. Polar grasslands – found in arctic polar region – organism – arctic wolf, fox, etc. – A
thick layer of ice remains frozen under the soil surface throughout the year – known as
permafrost – summer insects and birds appear.
Components: Structural Components:
I. Abiotic Components → abiotic components are physical components present in soil
& atmosphere (Ex) temperature, light, rainfall, minerals.
II. Biotic Components
Producers → plants absorbs sunlight & produce food by photosynthesis. Ex-trees,
shrubs, plants Consumers
Primary consumers → Called herbivores/plant eaters- depend on plants for food. Ex.
Insects, rat, goat, deer, cow, horse etc.
Secondary consumers → Called primary carnivores/meat eaters. Depend on herbivores
for food Ex. Frog, birds, cat, snakes, foxes etc.
Tertiary consumers → Called Secondary carnivores, feed on secondary consumers. Ex:
Tigers, lions etc.
Decomposers → Organisms which feed on dead organisms, plants & animals &
decompose into simpler compounds.
DESERT ECOSYSTEM Desert occupies about 35% of our world’s land area. It is
characterised by less than 25 cm rainfall. The atmosphere is dry.
Types:
1. Tropical desert-found in Africa-Sahara and Rajasthan – Thar
2. Temperate desert-south California-Mojave
3. Cold desert-China-Gobi desert
Characteristics:
1 Air is dry.
2 Climate is hot.
3 Annual rainfall is less than 25 cm.
4. Vegetation is poor Structure and functions of the desert Ecosystems
1. Abiotic Components - Eg. Temperature, rainfall, sunlight, water, etc.
2. Biotic Components
1. Producers Eg. Shrubs, bushes, some grasses and few trees. In deserts mostly
Succulent (e.g., cacti) plants are found available. They have waxy layer on the outside to
protect them from the sun.
2. Consumers Eg. Squirrels, mice, foxes, rabbits, deer and reptiles These animals dig
holes in the ground to live in. Most of the animals can extract water from the seeds they
eat.
AQUATIC ECOSYSTEM:
It deals with water bodies and biotic communities present in them- Classified as fresh
water and marine ecosystems. Fresh water systems are classified as lentic and lotic
ecosystems.
1. Pond Ecosystem: A Pond as a whole serves a good example of freshwater
ecosystem
 Abiotic Components: The chief components are heat, light, pH of water, CO 2,
oxygen, calcium, nitrogen, phosphates, etc.
 Biotic Components: The various organization that constitute the biotic component
are as follows:
a) Producers: These are green plants, and some photosynthetic bacteria. The producer
fix radiant energy and convert it into organic substances as carbohydrates, protein
etc
b) Macrophytes: These are large rooted plants, which include partly or completely
submerged hydrophytes, eg Hydrilla, Typha etc.
c) Phytoplankton: These are minute floating or submerged lower plants eg algae.
d) Consumers: They are heterotrophs which depend for their nutrition on the organic
food manufactured by producers.
 Primary Consumers: – Benthos: These are animals associated with living
plants ,detrivores and some other microorganisms –Zooplanktons:
These are chiefly rotifers, protozoans, they feed on phytoplankton
 Secondary Consumers: They are the Carnivores which feed on herbivores, these
are chiefly insect and fish, most insects & water beetles, they feed on
zooplanktons.
 Tertiary Consumers: These are some large fish, turtles, which feed on small fish
and thus become tertiary consumers.
 Decomposers: They are also known as microconsumers. They decompose dead
organic matter of both producers and animal to simple form. Thus they play an
important role in the return of minerals again to the pond ecosystem, they are
chiefly bacteria, & fungi.
2.Ocean Ecosystem: This is more stable than pond ecosystem, they occupy 70 % of
the earth surface.
 Abiotic Components: Dissolved oxygen, light, temperature, minerals.
 Biotic Components:
  Producers: These are autotrophs and are also known Primary producers. They
are mainly, some microscopic algae (phyto-planlanktons) besides them there are
mainly, seaweeds, as brown and red algae also contribute to primary production.
 Consumers: They are all heterotrophic macro consumers
 Primary Consumer: The herbivores that feed on producers are fish, etc.
 Secondary Consumers: These are carnivores fish feeding on herbivores.
 Tertiary Consumers: These includes, other carnivores fishes like Sea Turtle,
Sharks etc.
 Decomposers: The microbes active in the decay of dead organic matter of
producers, and animals are chiefly, bacteria and some fungi.
3.River Ecosystem: As Compared with lentic freshwater (Ponds & lakes), lotic waters
such as streams, and riverhave been less studied. However, the various components of
an river and stream ecosystem can be arranged as follows.
 Producers: The chief producers that remain permanently attached to a firm
substratum are green algae as Cladophora, and aquatic mosses.
 Consumers: The consumers show certain features as permanent attachment to
firm substrata, presence of hooks & suckers, sticky undersurface, streamline
bodies, flattened bodies.. Thus a variety of animal are found, which are fresh
spongy and caddis-fly larvae, snails, flat worms etc.
 Decomposers: Various bacteria and fungi like actinomycetes are present which
acts as decomposer.