UNIT-II
ECOSYSTEMS AND BIODIVERSITY AND ITS CONSERVATION
Definition of Ecosystem: A group of biotic communities of species interacting with one
another and with their non-living environment exchanging energy and matter.
STRUCTURAL COMPONENTS OF ECOSYSTEM:
Structural components of Ecosystem
Abiotic
Inorganic
Organic
Biotic
Climatic
factors
Autotrophs
Macro Consumers
Hetrotrophs
Micro Consumers
Decomposers
Primary
Consumers
Secondary
Consumers
Tertiary
Consumers
Top
Carnivores
Omnivores
The ecosystem comprises two major components:
1) Abiotic components and 2) Biotic components
ABIOTIC COMPONENTS: All non-living factors of an ecosystem is called abiotic
component. They are as follows:
i)
Inorganic substances: These include elements like C,H,O,N,P,S etc. They are
absorbed by the plants through the root hairs. With the help of sunlight, they are
converted into food material. These are again returned to the environment by the
process of decomposition.
ii)
Organic substances: These are proteins, Carbohydrates, lipids etc. They form a
link between the biotic and abiotic components of the ecosystem.
iii)
Climatic factors: They include physical factors like temperature, light,
atmospheric pressure, rainfall, humidity etc which varies according to the region.
BIOTIC COMPONENTS: All living organisms of an ecosystem constitute the biotic
components.
1. Producers: These are green plants (autotrophs) having chlorophyll. They
manufacture energy-rich food materials with the help of carbon dioxide, water,
sunlight through the process of photosynthesis. Eg: Green plants, photosynthetic
bacteria, chemosynthetic bacteria.
2. Consumers: All living organisms which have no chlorophyll must obtain their
energy from green plants directly or indirectly.
A) Macro consumers: These are large sized animals which depend upon plants
for their food. These include
i)
Primary consumers: These are herbivores which eat the green plants are
called primary consumers. Eg. Grasshopper, Deer, Rabbit.
ii)
Secondary Consumers: These are carnivores which eat the herbivores. Eg.
Frogs, centripedes, mollusks.
iii)
Tertiary consumers: These are carnivores which eat primary and
secondary consumers. Eg. Snake eating frogs, birds eating fishes.
iv)
Top Carnivores: Carnivores which are not killed and eaten by other
animals are called top carnivores. Eg. Lion, Leopard, Tiger
v)
Omnivores: They feed on both plants and animals Eg. Human beings, rat,
crow
B) Micro consumers: These are known as decomposers. They include chiefly
bacteria, fungi and actinomycetes. They feed upon dead organic matter, bring
about breakdown of the complex organic compounds into simple and soluble
compounds.
FUNCTIONAL COMPONENTS OF ECOSYSTEM
These include i) Trophic level ii) Food chain iii) Food web iv) Ecological pyramids
v) Energy flow vi) Biogeochemical cycles vii) Ecological succession
i) TROHIC LEVEL: All organisms with similar feeding habits are grouped together is
known as trophic level. It is denoted by T. All autotrophic plants belong to the first trophic
level (T1). Animals depending upon producers for their food resources occupy second trophic
level (T2). Third trophic level occupied by the animals depends on herbivores (T3). Top
carnivores occupy final level as (T4) in a linear way and the trophic level of decomposers is
denoted by (T5).
Producers
Herbivores
Carnivores
T1
T2
T3
Top Carnivores
T4
Decomposer T5
ii) FOOD CHAIN: The linear sequence of eating and being eaten in an ecosystem is
known as food chain. Energy-rich food materials pass from producers to primary consumers
(herbivores), from primary consumers to secondary consumers (primary carnivores) and
from secondary consumers to tertiary consumers (secondary carnivores) and so on. This
transfer of food energy from producers through a series of organisms is referred to a food
chain. It is classified into two types:
A) Grazing food chain: It stars with green plants and culminates in carnivores. Eg:
Grass
Rabbit
Snake
Grass
Zebra
Lion
Algae
Water fleas
Salmon
Hawk
Shark
B) Detritus food chain: It starts with dead organic matter which the detritivores and
decomposers consume. Thus it forms a link between dead organic matter and living
organisms.
Dead leaf litter
Crab
Salmons
Kingfisher
iii) FOOD WEB: It is a network 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. Eg:
Mice
Grass
Rabbit
Snake
Deer
Algae
Hawk
Lion
Water fleas
Salmons
Shark
Crab
Water beetles

Food chains and food webs play a very significant role in the ecosystem because the
two most important functions of energy flow and nutrient cycling take place through
them.

The food chains and food webs also help in maintaining and regulating the population
size of different animals and thus, help maintain the ecological balance.
iv) ECOLOGICAL PYAMIDS: Graphic representation of trophic structure and function
of an ecosystem, starting with producers at the base and successive trophic levels
forming the apex is known as an ecological pyramid. These are of three types
a) Pyramid of numbers: It represents the number of individual organisms at each trophic
level.
i) Upright: Here in a grassland ecosystem or pond ecosystem the organisms are
arranged according to their number. The base is occupied by more number of grasses then
followed by herbivores and carnivores and so on.
Shark
Salmons
Beetles
Algae
Top
carnivores
Carnivores
Herbivores
Producers
Lion, Tiger
Frogs, birds
Insects
Grasses
ii) Spindle: In a forest ecosystem big trees are less in number followed by herbivores
including, insects which form a much broader middle level and then carnivores and top
carnivores are still narrow at apex.
Top
Carnivores
Lion, Tiger
Snakes, Foxes
Carnivores
Herbivores
Insects
Producers
Trees
iii) Inverted: Here a few big trees occupy narrow base followed by fruit eating birds
acting like herbivores which are larger in number. A much higher number of lice, bugs etc,
grows as parasites on these birds, while still greater number of hyper parasites like bacteria
and fungi thus making inverted pyramid.
Hyper parasites
Bacteria, fungi
Lice, bugs
Parasites
Herbivores
Birds
Producer
Trees
b) Pyramid of biomass: It is based upon the total biomass at each trophic level in a food
chain. It is of two types
i) Upright: This pyramid indicates forest and grass land ecosystem where the
producers accumulates huge biomass while the consumers total biomass feeding on them
declines at higher trophic levels, resulting in broad base and narrowing top.
Carnivores
Frogs, birds
Herbivores
Producers
Rabbit, insects
Trees, Grasses
ii) Inverted: The biomass of producers are much less as compared to herbivores,
carnivores, and top carnivores so the pyramid shows an inverted shape with narrow base and
broad apex. As the water content in the producer level is high compared to other trophic
levels. This type of ecosystem is seen in pond, lake or ocean ecosystem.
Carnivores
Fishes
Herbivores
Water beetles
Producers
Algae
c) Pyramid Energy: The amount of energy at each trophic level is represented in this
pyramid. At each level there is a huge loss of energy (90%) and only 10% of energy is
transferred to next level. This also called as 10% law. Always the ultimate source of energy
is sun, so the pyramid of energy is always upright for any type of ecosystem.
Carnivores
1%
Herbivores
Producers
10%
100%
ENERGY FLOW IN THE ECOSYSTEM (10% LAW)
In any ecosystem the energy transfers from produces to a series of consumers. This energy
flow is always unidirectional. It obeys two basic laws of thermodynamics.
1st Law: The energy can neither be created nor be destroyed but it can be transformed from
one form to another.
2nd Law: The energy from a more concentrated to dispersed form.
UNIDIRECTIONAL FLOW MODEL
Producers convert solar energy to chemical energy but it cannot return the solar energy back
once it is converted. Similarly, the consumers build up potential energy by acquiring energy
from the producers, but it cannot return the same to the producers again. In this way the
energy once acquired cannot be sent back to its source. The flow of energy is always
unidirectional. The green plants conserve only 10% of total energy it receives as net primary
production. The rest is lost as heat energy. The primary net production is used by the
consumer but 90% of it is lost again as heat energy and 10% incorporated in the body of the
primary consumer as net energy. In this way the energy is transferred to the next levels.
UNIVERSAL FLOW MODEL
The flow of energy was explained by E.P. Odum as the universal flow model. Here it denotes
the energy storage at a particular level. In this model the input energy comes from a source
(solar energy, produces, herbivores) and stored in the form of standing biomass and
transferring to the next level some amount of energy is lost which gives an indication of
obeying the 2nd law of thermodynamics.
SINGLE CHANNEL FLOW MODEL
The flow of energy takes place in a unidirectional manner through a single channel from
producers to carnivores. This figure obeys the two laws of thermodynamics where after each
trophic level the energy is reducing to the next level. Some of the energy is transferred to the
surroundings in the form of respiration. Similarly some energy is wasted as not utilized and
not assimilated. As the flow of energy takes place, there is a gradual loss of energy at every
level, there by resulting in less energy available at next trophic as indicated by narrower
pipes (energy flow) and smaller boxes (stored energy in biomass).
DOUBLE CHANNEL OR Y –SHAPED FLOW MODEL
The modification of single channel flow model is the y-shaped model. This flow model
obeys the two basic laws of thermodynamics. The energy transfer from producers to
carnivores and also included decomposers and detritivores.
BIOGEOCHEMICAL CYCLES
Definition: The cyclic movement of chemical nutrients between living and non-living
environment is termed as biogeochemical cycles or nutrient cycles.
WATER CYCLE
Water covers about 73% of the earth’s surface. It occurs in rivers, lakes, oceans and seas etc.
From each of these water resources the water is continuously evaporated by the heart of the
sun and reaches the atmosphere. These water vapours condense higher altitude of the
atmosphere and form clouds. These clouds are moved by winds and pass over land where
further cooling takes place. At this point the water vapour precipitates to form rain, dew,
frost. Water falling in this way runs into streams, rivers and ultimately returns to the oceans.
During rainfall, some amount of water percolates into the deeper layers of the soil. The water
from the soil is absorbed by the roots of the plants and is returned to the atmosphere through
transpiration. Animals drink water and part of it is returned to the atmosphere through
evaporation and excretion. The continuous circulation of water from earth to atmosphere and
vice versa is termed as water cycle.
CARBON CYCLE
Carbon is the basic constituent of all organic components and accounts for 49% of the dry
weight of the organisms. The carbon cycle is the simplest of the mineral cycle. The reservoir
is the atmosphere from which the green plants take it in energy consuming process. In
photosynthesis the plants synthesis simple carbohydrates, which in turn are converted into
polysaccharides and complex fats in plants. These organic compounds are used by herbivores
and by carnivores. The dead bodies of the producers and consumers are eaten by
decomposers. The decomposers liberate carbon dioxide as a gas into the atmosphere. The
carbon is also released into the atmosphere directly as carbon dioxide in respiration of plants
and animals.
NITROGEN CYCLE
The atmosphere contains 79% of nitrogen and this large amount is not used by biotic
communities as such plants obtain nitrogen from their surroundings in the form of nitrate and
ammonia. Animals have their source in the form of amino acids. The movement of nitrogen
from reservoir takes place in the following steps:
a) Nitrogen fixation: The atmospheric nitrogen is converted into the biolotifally acceptable
form i.e. nitrates. It is of two types
i) Biological fixation: Few bacteria and cynobacteria are able to convert gaseous nitrogen
into nitrates eg: Azotobacter, Trichoderma etc.
ii) Atmospheric fixation: The oxygen of the atmosphere combines with molecular nitrogen in
the presence of lightning. It results in the formation of nitrogen oxides
N2 + 2[O]
2NO + 3[O]
2NO
N2O5
These oxides get dissolved in rain water and are washed down to earth as nitrous and nitric
acids. These acids react with alkali radicals of soil to form nitrates. The soluble nitrates are
directly absorbed by plants.
N2O5 + H2O
2HNO3 + CaCO3
2HNO3
Ca(NO3)2 + CO2 + H2O
b) Nitrogen assimilation: Nitrate is first reduced to ammonia which combines with organic
acids to form amino acids. The latter are used to synthesize proteins, enzymes, chlorophyll,
nucleic acids etc. The animals obtain their organic nitrogen from plant proteins. They are first
broken down to amino acids during digestion. Amino acids are then converted to animal
proteins, nucleic acids etc.
c) Ammonification: The proteins of dead bodies of plants and animals are returned to the
nitrogen cycle the release of ammonia from proteins and other nitrogenous compounds by the
action of microorganisms.
Proteins
H O
2
R-NH2
H O
2
R-OH + NH3
d) Nitrification: The process of conversion of ammonia into nitrate is called nitrification. The
process takes place in two steps. The common nitrite bacteria act on ammonia and convert it
to nitrites are further oxidized to nitrates by nitrobacter and nitrocystis.
e) Denitrification: Degradation of nitrate by denitrifers is known as denitrification. The
anaerobic bacteria causes denitrification is Micrococcus denitrificans, Bacillus licheniforms.
PHOSPHOROUS CYCLE
This is a sedimentary cycle. Phosphorus is a major constituent of nucleic acids, ATP and
Phospholipids etc. The major source of phosphorous is rock deposits. It occurs in the soil as
calcium phosphate, iron phosphate (or) aluminum phosphate. Through weathering and
erosion inorganic phosphate becomes available to plants in dissolved condition. It is then
passed on along the food chains and the excess is excreted out. The insoluble inorganic
phosphate is converted to soluble organic form by producers. In animals it may be deposited
as part of skeleton. The excretory materials and the dead bodies of the plants and animals are
acted upon by the decomposers and inorganic form of phosphate is released again.
ECOLOGICAL SUCCESSION
Definition: The successive colonization of different biotic communities in an area over a
period of time is known as ecological succession.
PROCESS OF SUCCESSION
Five major stages are involved in the process of succession
1. NUDATION: It includes a bare area with no vegetation or life. New area may develop on
account of various factors like volcanic eruptions, landslides, forest fires, large earthquakes,
deforestation etc.
2. INVASION: In this stage a species is established in a new area. This involves in three
stages.
a) Migration: This is the arrival of seeds, spores and vegetative propagules from other
places. This is affected by wind, water, animals and man.
b) Ecesis: The establishment of the pioneers in a new place is called ecesis. It consists
of germination, growth and reproduction.
c) Aggregation: The increase in the number of colonizing individuals is called
aggregation.
3. COMPETITION: Large number of individuals in a limited area, develops a competition
mainly for space and nutrition. The competition is mainly for space and nutrition. This may
be intraspecific (among the individuals of the same species) or interspecific (among
individuals of different species). In this competition the weaker one are eliminated and
stronger ones are retained. The weaker one act as a humus for the stronger ones.
4. REACTION: The reaction between new species and the environment takes place as a
result, increasing in relative humidity by transpiration, increase in rainfall etc.
5. STABILIZATION: The whole process of succession results in stabilization of the biotic
communities and in the development is called as climax community.
TWO TYPES OF SUCCESSION
HYDROSERE: The type of succession starts in water which culminates in a climax. The
pioneer community consists of phytoplanktons, which are free floating algae, diatoms etc.
Gradually these are replaced by rooted submerged plants followed by rooted-floating plants.
Growth of these plants keep on adding organic matter to the substratum by death and decay
and thus a layer of soil builds up and shallowing of water takes place. Then Reed swamp
stage follows in which the plants are partly in water and partly on land. This is followed by a
sedge-meadow stage of grasses then by a woodland consisting of shrubs and trees and finally
by a forest acting as climax.
XEROSERE: This type of succession originates on a bare rock, which lacks water and
organic matter. The pioneer community here consists of crustose and foliose lichens. These
lichens produce some weak acids and help in disintegrating the rock a process known as
weathering. Their growth helps in building up gradually some organic matter, humus and
soil. Then comes the community of mosses, followed by herbs, shrubs and finally the forest
trees.
MAJOR ECOSYSTEMS
FOREST ECOSYSTEM
Forest is natural plant communities with dominance of trees. The major forest biomes found
in India are Tropical rain forests, Tropical deciduous forests, Temperature broad leaved
forests, Temperate needle leaf or coniferous forests.
ABIOTIC COMPONENTS
It includes inorganic and organic substances present in the soil and atmosphere. The climate
(temperature, light, rainfall etc) and soil (minerals) vary from forest to forest.
BIOTIC COMPONENTS
i) Producers: These are mainly trees that show much species diversity. In different forests
producers are Butea frondosa, Tectona grandis, Dipterocarpus, Shorea robusta, Quercus,
Pinus, Cedrus, Picea and Abies.
ii) Consumers: These are animals which are grass eating and flesh eating. The insects like
ants, flies, beetles, leaf hoppers, bugs and animals like shrews, moles, deer, flying foxes,
lizards, fox, lion, tiger.
iii) Decomposer: These are microorganism which may be bacteria like Bacillus, Clostridium
and fungi like Aspergillus and Alternaria.
GRASSLAND ECOSYSTEM
This type of ecosystem occurs in those areas where the climate is cold during winter and hot
during summer.
ABIOTIC COMPONENTS
This includes the nutrients or elements present in the soil. Thus elements like carbon,
hydrogen, oxygen, nitrogen, sulphur, phosphorus etc are provided by water, carbon dioxide,
nitrates, phosphates and sulphates present in air and soil of the areas.
BIOTIC COMPONENTS
i) Producers: There are no trees, only herbaceous plant cover dominated by a wide variety of
grass species is present. Main grass species are Dichanthium, Cynodon, Phragmites, Imperata
etc.
ii) Consumers: These include deer, sheep, rabbits, mice. Some insect species such as
Cicindella, Coccinella, Dysdercus, Termites, millipedes, jackals, fox, hawks, snakes etc are
present.
iii) Decomposers: This include Aspergillus, Mucor, Rhizopus, Penicillium, etc which
decomposes the dead and decay parts.