UNIT-2 ECOSYSTEMS & BIODIVERSITY

ECOSYSTEM
“Eco-system is defined as a self regulating group of biotic communities of species
interacting with their non living environment exchanging energy and matter.”
Study of ecosystems is called as Ecology or the study of organisms in their natural home
interacting with their surroundings is called Ecology.
STRUCTURE OF ECO-SYSTEM
The structural attributes (components) of these components are:
 Biotic components
 Abiotic components
1. Biotic components: These constitute all the living members of an eco-system.
Ex. Plants, animals and micro organisms. These are of three types:
 Producers
 Consumers
 Decomposers
Producers- These are constituted mainly by green plants. Green plants trap solar energy and
converts into potential chemical energy in the process called photosynthesis. These species
are also known as Photo- autotrophs.
The plant species which live inside the ocean waters prepare their food in the absence of
sunlight by the oxidation of chemicals and they are known as chemo-autotrophs and the
process is called chemosynthesis. (Sulphur bacteria)
Consumers- Organisms which get their food by feeding on other organisms are called
consumers.
a. Herbivores- they feed on plant species (primary producers) eg- rabbit, insects
b. Carnivores- they food on herbivores and other carnivores eg- frog, snake
c. Omnivores- they feed on both plants and animals. Eg- humans
d. Detritivores- they feed on parts of dead organisms, waste of living organisms etc. Eg-
earthworms, ants.
Decomposers- they derive their food by breaking down the complex organic molecules to
simple organic compounds and finally to inorganic nutrients. Eg- bacteria, fungi
2. Abiotic components: - Abiotic components of an eco-system consist of non living
substances and factors. They are broadly divided into Physical and chemical factors.
 Physical factors include temperature, wind, soil type, water availability, humidity,
precipitation, light, etc.
 Chemical factors include nutrients like Carbon, Nitrogen, Phosphorous, potassium,
topography, pH of the soil, etc.

FUNCTIONS OF ECO-SYSTEM:
Eco-systems have some functional attributes due to which components remain and running
together. The tendency of every eco-system depends on various function performed by the
structural components of the eco-system.
The main functional attributes of eco-system are:
I. Food Chain & Food Web.
II. Energy flow
III. Ecological pyramids
IV. Ecological regulation
V. Ecological succession
I. Food chain: The transfer of food, energy from producers through a series of
organisms with repeated eating and being eaten is known as a food chain.

Grasshopp
Grass Frog Snake Peacock
er

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Types of food chains: There are 2 types of food chains:

a. Grazing food chain: This type of food chain starts from the living green plants goes
to grazing herbivores and onto carnivores, eco-systems with such type of food chains
are directly depend upon the influx of the solar radiation. Most of the eco-systems in
nature follow this type of food chain.

Grass Rabbit Lion

b. Detroiter’s food chain: This type of food chain goes from dead organic matter into
micro organisms and then to organisms which feed on detritivors (decomposers) and
predators. Such eco-systems are not dependent on direct solar energy and chiefly depend
upon the influx of dead organic matter produced in other eco-systems. Ex: bacteria and fungi
feeding on dead organic matter and are eaten by small fish which act as prey to large fish or
birds.

micro-
Dead and Decay small fish big fish/birds
organisms

Food webs: A complex network of interconnected food chains of different tropic levels in a
Biotic community is termed as a food web.
The complexity of any food web depends upon the diversity of organisms in that ecosystem.
Thus, each species of any eco-system is indeed kept under some sort of a natural check so
that the eco-system may remain balanced and this is the significance of a food web.
Example-

Significance of food chain & food web-

a. They maintain the ecological balance by regulating the nutrient cycles.
b. Biological magnification- It is a process in which the concentration of the non-
biodegradable material or any fertilizer accumulates in the food chain. As human
beings occupy the highest position in the tropic level, they get highly bio-magnified
which is harmful. Ex:- DDT (dichloro diphenyl trichloro ethane) is an insecticide used

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for killing insects. Excess usage of this non-biodegradable chemical makes the soil
over nourished and its concentration increases as it passes along the food chain.

II. Energy flow- All eco-systems are energy driven complexes. The energy concerned
to eco-system is light energy, chemical energy, heat energy and the source of all these
energies is “solar energy”. This energy gradually transfers to light, chemical and heat energy.
1% of total energy falling on plants used for photosynthesis and this is only source of energy
for proper functioning of the eco-system.
The fixation of solar energy by the plants and its utilization in the form of food by
living organisms obey the 2 laws of thermodynamics.
1st law: Energy can neither be created nor destroyed; it can only transfer from one form to
another.
2nd law: It states that every transformation of energy is accompanied by a simultaneous
degradation of energy from concentrated form to disperse. Flow of energy is always uni-
directional.
Energy Flow Models:
Energy flow in various trophic levels of an ecosystem can be explained with the help of
various energy flow models. They are;
A. Universal Energy Flow Model
B. Single Channel Energy Flow Model
C. Double channel or Y-shaped flow model
Universal energy flow model:
This model tells, as the energy flow takes place, there is a gradual loss of energy at every
level as indicated in the picture. This occurs mainly due to respiration, locomotion and other
metabolic activities.

Single energy flow model:

The flow of energy takes place in a unidirectional manner through a single channel of
producers to top carnivores, and illustrated the gradual decline in energy level due to loss of
energy at each successive trophic level in a grazing food chain.

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Double channel or Y-shaped flow model:

In nature, both grazing and detritus food chain operate in the same ecosystem. However, it is
the grazing food chain which predominates. The double channel or Y-shaped flow model of
energy flow shows the passage of energy through two food chains which are separated I time
and space.

III. Ecological pyramids:

The graphical representation of structure and function of tropic levels of an ecosystem,
starting with producers at the top and each successive tropic level forming the apex is known
as an ecological pyramid.
In a food chain starting from the producers to the consumers, there is a regular decrease in the
properties (i.e., energy, biomass and the number of organisms) Since some energy is lost in
each tropic level, it becomes progressively smaller at the top.
Ecological pyramids are of three types:

1. Pyramid of Numbers
2. Pyramids of Energy and
3. Pyramid of Biomass
Pyramid of Numbers It represents the number of individual organisms present in each
tropic level.
Ex: A grassland Ecosystem
Producers are grass (small in size and large in number. Hence they occupy the first tropic
level. The primary consumers are rats occupying the second tropic level. It is worthwhile to
note that rats are less in number than grass. Secondary consumers are snakes which occupy
the third tropic level and they are lesser in number than rats. Tertiary consumers are Eagles
that occupy the next tropic level. This is the last tropic level where the number and size of the
tropic level is the least as shown in the diagram.

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Pyramid of Energy It represents the amount of energy present in each tropic level. The rate
of energy flow and the productivity at each successive tropic level is shown in the figure
below.
At every successive tropic level, there is a heavy loss of energy (almost 90%) in the form of
heat. Thus, at each tropic level only 10% is transferred. Hence there is a sharp decrease in
energy at each and every successive tropic level as we move from producers to top
consumers (carnivores).
Pyramid of energy is depicted in the figure below.

Pyramid of Biomass: It represents the total amount of biomass (mass or weight of

biological material) present in each tropic level. Considering the example of a forest
ecosystem, there is a steady decrease in the biomass from the lower tropic level to the higher
tropic level. The producers (trees) contribute a major amount of the biomass. The next tropic
levels are the herbivores (insects and birds) and carnivores (snakes, foxes, etc). The top of the
tropic level consists of very few tertiary consumers (Ex: Lions and Tigers) whose biomass is
very low. The pyramid of biomass is shown below

Ecological production: The rate of production of organic matter or biomass is called

productivity.
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This is of 2 types:
i) Primary productivity: it is defined as the rate at which the radiant energy is converted
into organic substances by photosynthesis or chemo-synthesis by the primary producers. It is
of 2 types:
GPP (Gross Primary Productivity): The rate at which the producers are able to utilise the
radiant energy in photo or chemo synthesis to produce their food is called GPP.
NPP (Net Primary Productivity): The rate at which the energy or organic matter is stored in
a producer after respiration is called NPP.
Thus, NPP = GPP-R (R= Respiratory loss)
ii) Secondary productivity: The energy stored at consumer level for use by the next trophic
level is known secondary production.

IV. Ecosystem Regulation:

Ecosystem itself tries to resist to any environmental stress tries to disturb the normal
ecosystem and maintain the equilibrium with the environment. This property is known as
Homeostasis.
However, the system can show this tolerance or resistance only within a maximum and a
minimum range, which is known as Homeostatic Plateau. Within this range, if any stress
tries to cause a deviation, then the system has its own mechanism to counteract these
deviations which are known as Negative Feedback Mechanisms. These negative feedback
mechanisms try to bring the system back to its ideal conditions. But, if the stress is too high
and beyond the range of homeostatic plateau, then another type of mechanism known as
Positive Feedback Mechanisms start operating and accelerate the deviations. So these kinds
of mechanisms take the system away from its ideal conditions and leads to environmental
disasters.

V. Ecological succession: Any community tries to maintain the equilibrium with the
prevailing condition of the environment. It changes with the changing environmental
conditions. Sometimes the activities within the community itself or environmental changes
can effect a change in the community. Eco-system development may be defined as “it is an
orderly process of community development that involves changes in species structure of
community processes.” Finally it ends in a stabilized eco-system.
The community which develops as initial community is known as pioneer community.
The transitory communities are called as “seral stages” or developed stages.
When a system gets stabilized i.e. the final community which lasts for a longer
period is known as “climax community”.
Process of succession: The whole process of succession is completed through a number

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of sequential steps which follows one another. Those are:

 Nudation
 Invasion
 Competition & co-action
 Reaction
 Stabilization
Nudation: This is the development of bare area without any form of life. This area may
develop due to topographic (soil erosion by gravity, water, wind, land slides, volcanic
activity, earth quakes etc.) or climatic like floods drought conditions, melting of glaciers,
storms and biotic factors.
Invasion:
This is the successful establishment of life in that area. The species actually reaches that area
from other places the forces of migration and dispersal. After reaching the new area the
process of successful establishment of special is known as “ecesis”. In plants seeds
germinate, seedlings grow and adults start to reproduce and increase their number, this
process is called “aggregation”.
Competition and co-action:
After aggregation large number of individuals of species increase in a limited area, develops
competition and co-action for space and nutrition. In this process changes within the
community can be observed and the species is unable to complete with other number of
individuals would be discarded.
Reaction:
This is the most important stage in the process of succession. The mechanism of modification
of environment through the influence of living organisms starts in this stage. As a result of
this process changes takes place in soil, soil structures, water ph, light conditions,
temperature etc. of the environment. Due to all these the environment is modified and
becoming unsuitable for the existing community which sooner or later is replaced by another
community.
Stabilization:
Finally there occurs a stage in the process. Then the final community or terminal community
becomes more or less stabilized for a longer period of time and it can be maintain itself on
equilibrium with the environment or surrounding or climate of the area.

The process of ecological succession

Example of Ecological Succession:

1) Hydrosere (Hydrarch): This type of succession start in a water bodies like pond and
culminates in a climax community which is forest. It has following stages:
a) Phytoplankton stage: These are the pioneer community. Mainly blue green algae,
green algae, diatoms and bacteria etc.
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b) Rooted submerged stage: Due to death and decomposition of phytoplankton organic

matter start accumulating on the pond subsurface. This new environment is favorable
for the growth of rooted submerged hydrophytes like Hydrilla, Elodea etc.
c) Rooted submerged stage: Now the depth of lake reduces to 2-5 feet, favoring the
growth of rooted hydrophytes with their large leaves floating on the water surface.
Example: Nelumbo, Trapa, Azolla etc.
d) Reed-swamp stage: also known as amphibious stage as the plants of community are
rooted but most of it part is in air. Example: Scirpus, Sagittaria etc.
e) Sedge-meadow stage: They form mat like vegetation, results into higher loss of
water through evapotranspiration process. The marsh like condition in the previous
stage is removed and area with soil moisture left. Example: carex,cyperus etc.

f) Woodland stage: As the marsh land disappear soil become more dry and give rise to
vegetation like shrubs( Salix, cornus) and trees ( populus, Alnus).
g) Forest stage: This is climax community. It can developed as tropical rain forest or
mixed forest depending upon the climate of the region. Example: Ulmus, Acer and
Quercus.

Lithosere: A Xerosere on Rock: It start with bare rock and culminate into a forest stage.
Different stages of Lithosere are as follows:
a) Crustose lichen stage: The lichen are the pioneer community. The substratum is very
poor in moisture and organic matter, subjected with extreme of temperature.
Examples: Rhizocarpon, Rinodina etc.
b) Foliose lichens stage: They can absorb more water and retain more water and are
able to accumulate dust particle which further help in build up of substratum.
Examples: Parmelia, Dermatocapron.
c) Moss stage : Xerophytic mosses such as Tortula, Grimmia appears after lichens stage.
d) Herbs stage: due to growth of mosses there is more accumulation of soil.This stage is
constituted by shallow rooted grasses such as Aristida,Festuca etc which further
replaced by shrubs.
e) Shrub stage: Species like Rhus, Phytocarpus start growing in the area, which over
compete the herbaceous species.
f) Forest stage: This is the climax community for this type of ecological succession.
Starting with Xerophytic tree species it changes into mesophytic type and finally into
forest type.

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