To be discussed:
1. Ecosystem(structure and function)
2. Food chain, food web, and ecological pyramids
3. Nutrient cycles
4. Different ecosystems( forest, desert, lake, grasslands, and ocean)
The term ecosystem was coined by A.G. Tansley (1953). Ecosystem is
defined as a natural unit consisting of all plants, animals and micro-
organisms (biotic factors) in an area functioning together with all of the
non-living physical (abiotic) factors of the environment.
An ecosystem is a self regulating group of biotic communities of species
interacting with one another and with their non-living environment exchanging
energy and matter.
The term Ecology was coined by Earnst Haeckel (1869). The term ecology is
derived from Greek words Oikos (home) and Logos( study). So it deals with
the study of organism in their natural home interacting with their environment.
The Ecology is also defined as study of the structure and functions of an
The ecosystem can be Natural such as forests, grasslands, deserts, and
aquatic ecosystems such as ponds, rivers, lakes, and the sea and human
modified such as agricultural fields and aquarium.
• Structure and function of ecosystem:
1) Structural features of Ecosystem: Composition and organization of
biological communities and abiotic components constitute the structure of an
(A)Biotic component: The plant, animal and microorganism present in an
ecosystem forms the biotic component. They are divided based on the way
they get their food
1) Producers: They generate food by their own. They can be Photo
autotrophs( mainly green plants) which produces organic matter in
presence of sun light through photosynthesis and chemo-autotrophs
( produce organic matter through chemical reaction) such as sulphur
oxidizing or reducing bacteria, nitrifiers , methanogens.
1) Consumers: They get their food by feeding upon either plants or other
organisms. They can by divided into
a) Herbivores (plant eaters): They feed directly on producers for their food
and also known as primary consumers. Ex- rabbit, insects, man.
b) Carnivores ( meat eaters) : They feed on consumers and can be called
secondary consumers ( if feeds on herbivores . Example: frog) or tertiary
consumers( feeds upon secondary consumers, example: snake, big fish).
c) Omnivores: They feed on both plants and animals. Example: Humans, rat,
3) Decomposers or Saprotrophs: They derive their nutrition by breaking
down the dead organic material to simpler organic compounds and
ultimately into inorganic nutreints. Examples: Bacteria, fungi and
actinomycetes are decomposer. Decomposition is a vital function in nature
as without this all the nutrient would be tied up in dead matter and no new
life will be produced.
Most ecosystem are highly complex and consist of an
extremely large number of individuals of a wide variety of species. Some
species of plant and animals are extremely rare and may occur only at a
few locations. These are said to be endemic to these area.
B) Abiotic component: It include air, water, soil and can be divided into:
1) Climatic component: include, sunlight and shade, average temperature,
rainfall, wind pattern, humidity of a particular area. Most of the climatic
parameters occurs in the lower atmosphere known as troposphere.
2) Edaphic component: Soil is the major source of mineral nutrients for plants
and other organisms. Soil fertility is determined by nutrient availability, the
water holding capacity and aeration of the soil.
Soil profile: It is the sequence and nature of the horizons (layers)
superimposed one above the other and exposed in a pit section dug through
the soil mantle. In a longitudinal section of soil, three distinct layers (A, B
and C horizons) can be seen. Sometime we also observe O layers which is
present above the surface of mineral matrix and mainly composed of fresh or
partially decomposed organic matter.
The uppermost A : horizon is the most important one in which seeds are
grown and from which plants derive nutrition. These are rich in organic matter
and show downward loss of soluble salts, clay, iron and know as zone of
B- horizon : it contains less organic matter and is hence less fertile as
compared to horizon A. The chemical leached from A horizon , collects in this
zone. Also know as zone of illuviations.
C – horizon : which is a mineral layer made of incompletely weathered large
masses of rocks.
A horizon: Organic matter, roots,
worms, insects, small rock
and mineral fragments. Dark in
B horizon: Some roots and
other living organisms, materials
leached by water from the A
horizon, clay, rock fragments,
minerals. Lighter in color than
C horizon: Weathered parent rock
materials leached by water
from the B horizon, partly weathered
rock fragments. yellowish color.
So overall abiotic component can be divided into:
1) Physical factors: It include climatic, edaphic, geographical factor such as
latitude and altitude, Soil type, water availability, water current etc. The
variation in these physical parameter decide the type of ecosystem
characteristics. The solar flux, temperature and precipitation pattern shows
mark difference in a desert ecosystem, tropical or tundra ecosystem.
1) Chemical factors: Availability of major essential nutrient such as carbon,
nitrogen, phosphorous, level of toxic substances, salts affects the
functioning of an ecosystem.
Function attributes of an ecosystem: The major functional attributes of an
ecosystems are as follows:
a) Food chain, food webs and trophic structure b) Energy flow
a) Cycling of nutrients (Biogeochemical cycles)
a) Primary and secondary production
a) Ecosystem development and regulation
Food chains: The sequence of eating and being eaten in an ecosystem is
known as food chain. All organism, living or dead are potential source of food
for some other organism and thus there is essentially no waste in the
functioning of a natural ecosystem.
Example of food chain:
Grass grasshopper Frog Snake Hawk ( Grassland
Phytoplankton water fleas small fish Tuna ( Pond ecosystem)
Lichens reindeer Man ( Arctic tundra)
Each organism in the ecosystem is assigned a feeding level or trophic level
depending upon its nutritional status. So in grassland ecosystem grass
constitute the 1st trophic level, grasshopper 2nd, frog 3rd and snake and hawk
occupy the 4rd and the 5th trophic levels, respectively.
The decomposer consume the dead matter of all these trophic level.
In nature we come across two type of food chain in ecosystem:
1) Grazing food chain: It starts with green plants( primary producer) and
culminates in carnivores. Examples:
Grass Rabbit Fox
Phytoplankton water fleas small fish Tuna ( Pond ecosystem)
2) Detritus food chain: It start with dead organic matter which the detritivores
and decomposer consumes. Partially decomposed dead organic matter
and even the decomposers are consumed by detritivores and their
Leaf litter algae crabs small carnivorous fish large carnivorous fish
Dead organic matter fungi Bacteria ( Forest ecosystem)
Food web: Food chain in ecosystem are rarely found to operate in isolated linear
sequence. Rather they are found to be interconnected and usually form a complex
network with several linkages and are known as food web. Food web is a network of
food chain where different types of organisms are connected at different trophic levels,
so that there are number of option of eating and being eaten at each trophic level.
Food webs give greater stability to the ecosystem, as if one species become extinct or
suffers then the species in the subsequent trophic level are also affected in food chain,
however in case of food web effect will be reduced due to presence of other food
Significance of food chains and food webs:
1) Plays significant role in ecosystem as flow of energy and nutrient cycling take
place through food chain and food webs.
1) Food chain and food webs also help in the maintaining and regulating the
population size of different animals thus maintain the ecological balance.
1) Food chain shows a unique property of biological magnification of some
chemicals. Pesticides for examples DDT or other chemical which are non-
biodegradable in nature. Such chemicals are not decomposed or excrete out so their
concentration keep on increasing at each successive trophic level. This
phenomenon is know as biomagnification or biological magnification.
Trophic structure: The producer and consumer are arranged in the ecosystem in a
definite manner and their interaction along with population size are expressed together
as trophic structure. Each food level is known as trophic level and the amount of living
matter at each trophic level at a given time is known as standing crop or standing
Ecological Pyramids: Ecological pyramids were first devised by British
ecologist Charles Elton(1927). Ecological pyramids is graphical representation
of trophic structure and function of an ecosystem, starting with producers at
the base and successive trophic level forming the apex is known as an
ecological pyramid. It is of three types:
1) Pyramid of numbers: It represent the number of individual organisms at
each trophic level. It may be upright or inverted pyramid of number depending
upon the type of ecosystem and food chain. Example:
Top carnivores Top carnivores
birds Carnivores Snakes, Foxes
Herbivores Insects, birds
Forest ecosystem ( narrow on
Grassland ecosystem ( upright) both end and broader in the
Hyper parasite Fleas, microbes
Parasite Lice, bugs
Parasitic food chain( Inverted)
2) Pyramid of Biomass: It is based upon the total biomass (dry weight) at
each trophic level in a food chain. It can be upright or inverted. Example:
Tertiary Carnivores Big fish
Carnivores Small fish
Snake, frog, birds
Herbivores Squirrel, rabbit, insect producer phytoplankton
Producer Tree, herbs, grasses
3) Pyramid of energy: The amount of energy present at each trophic level is
considered for this type of pyramid. It is always upright, because there is
huge loss of energy (about 90%) in the form of heat and respiration at each
successive trophic level. Thus at each energy level only 10% of the energy
0.1 Top carnivores
Pyramid of energy
Flow of energy in an ecosystem: Flow of energy in an ecosystem takes place through
food chain and necessary for the sustenance of an ecosystem. In an ecosystem energy
flow is always unidirectional unlike nutrient which moves in a cyclic manner in an
ecosystem. The energy flow in an ecosystem follows the law of thermodynamics:
1st law of thermodynamics: energy can neither be created nor be destroyed but it can
be transformed from one form to another. In ecosystem green plant( producers)
transform solar energy to biochemical energy which then travels to other trophic
2nd law of thermodynamics: energy dissipates as it is used or in other word it get
converted from a more concentrated to dispersed form. In case of food chain also
energy dissipate at every trophic level. The main loss of energy takes place through
heat and respiration. At every level there is about 90% loss of energy and the energy
transferred from one trophic level to another is only 10%.
Nutrient Cycling: Nutrient cycling is another functional aspect of ecosystem. Nutrient
like Carbon, nitrogen, sulphur, phosphate moves in a circular path through biotic and
abiotic components and therefore known as biogeochemical cycle. The nutrient too
move through food chain and ultimately reach the detritus compartment( containing
dead organic matter) where various micro-organism carry out decomposition. In the
decomposition process dead organic matter converted into inorganic substances by
microbial decomposition which are again used up by plant.
Organic matter Organic matter
Inorganic molecule decomposer
Simplified nutrient cycle in ecosystem
• The main component of the nitrogen cycle starts with the element nitrogen in
• Nitrogen in the air becomes a part of biological matter mostly through the
actions of bacteria and algae in a process known as nitrogen fixation.
Legume plants such as clover, alfalfa, and soybeans form nodules on the
roots where nitrogen fixing bacteria take nitrogen from the air and
convert it into ammonium, NH4. The ammonia is further converted by
other bacteria first into nitrite ions, NO2, and then into nitrate ions, NO3.
Plants utilize the nitrate ions as a nutrient or fertilizer for growth. Nitrogen
is incorporate in many amino acids which are further reacted to make
• Ammonia is also made through a synthetic process called the Haber
Process. Ammonia may be directly applied to farm fields as fertilizer.
Ammonia may be further processed with oxygen to make nitric acid. The
reaction of ammonia and nitric acid produces ammonium nitrate which
may then be used as a fertilizer. Animal wastes when decomposed also
return to the earth as nitrates.
• To complete the cycle other bacteria in the soil carry out a process known
as denitrification which converts nitrates back to nitrogen gas.
The oxygen cycle is the biogeochemical cycle that describes the movement of oxygen
within and between its three main reservoirs: the atmosphere (air), the biosphere
(living things), and the lithosphere (Earth's crust).
By far the largest reservoir of Earths oxygen is within the silicate and oxide minerals
of the crust and mantle (99.5%). Only a small portion has been released as free oxygen
to the biosphere (0.01%) and atmosphere (0.36%).
The main source of atmospheric oxygen is photosynthesis, which produces sugars and
oxygen from carbon dioxide and water:
6CO2 + 6H2O + energy → C6H12O6 + 6O2
An additional source of atmospheric oxygen comes from photolysis, whereby high
energy ultraviolet radiation breaks down atmospheric water and nitrous oxides into
2H2O + energy → 4H + O2
2N2O + energy → 4N + O2
The main way oxygen is lost from the atmosphere is via respiration and decay,
process in which animal life and bacteria consume oxygen and release carbon dioxide.
Chemical weathering of exposed rocks also consumes oxygen.
4FeO + O2 → 2Fe2O3
Primary Production: The rate at which radiant energy is converted into organic
substances by photosynthesis or chemo-synthesis by the primary producer. It is also
known as gross primary production (GPP).
Net Primary Production( NPP) : Some part of the organic matter produce during
photosynthesis get used during respiration process to produce energy for the
sustenance of the primary producer, so the amount of remaining organic matter left
is known as Net primary production (NPP).
GPP = NPP + R
Secondary Production: The plant energy is used up for producing organic matter of
the herbivores which, in turn is used up by carnivores. The amount of energy stored
by the herbivores or carnivores( in excess of respiratory loss) is known as secondary
In other word we can say that energy stored at consumer level for use by the next
trophic level is known as secondary production.
Wet tropical forest and Estuarine ecosystem are highly productive ecosystem and
needed to conserve.
Ecological Succession: Ecosystems are dynamic in nature and often changes its
structure and function due to change in the physical environment or change in the
biotic composition. Some of these changes are very orderly and can be
During this change process one type of a biotic community is totally replaced by
another type of community over a period of time and this transition continue till
a stabilized biotic community sets up. This transition process is known as
Ecological succession is defined as an orderly process of changes in community
structure and function with time mediated through modifications in the physical
environment and ultimately culminating in a stabilized ecosystem known as
Type of succession:
Primary Succession: It start from the primitive substratum, where their was no
living matter present before. It is a slow process due to lack of any build up
Secondary succession: It starts from previously built up substrata where their was
presence of living matter before. Due to external factor existing community
disappear . These processes are fast.
Succession can be autogenic (induced by community itself) or allogenic( due to
Pioneer community: The first group of organism established in a particular area
is known as pioneer community.
Seral stages or sere: The whole sequence of communities which are transitory
between from Pioneer to climax community are known as Seral stages.
Climax community: It is the stabilized community formed in the end of
succession process which is in equilibrium with the environment.
Ecological Succession type: Based on the substrata type :
Hydrarch or Hydrosere: It start in watery area like, pond, swamp,bog.
2) Mesarch: starting in the area of adequate moisture.
3) Xerarch or Xerosere: Starting in dry area with little moisture. It can be of
Lithosere: starting on a bare rock
Psammosere: starting on sand
Halosere: starting on saline soil.
Process of succession: Succession take place in a systematic order of sequential
Nudation: It is development of bare area without any life form. This formation
can be due to landslide, volcanic eruption (topographic factor), or due to
drought, glaciers ( climatic factor) or due to overgrazing, disease outbreak
( biological factor).
Invasion: This is successful establishment of a species in a bare area. It start
with migration or dispersal process where seeds, spores reach the bare area
through air, water etc.
After migration successful establishment of the species( adjustment with the
prevailing condition) is know as ecesis.
After ecesis , number of species increase in number due to reproduction and come
closer to each other a process know as aggregation.
3) Competition and Coaction: As the number of individuals grows there is
competition, both inter-specific( between different species) and intra-specific
( within the same species) for space, food and water. Individuals of species affects
each other life in various ways and this is known as coaction.
4) Reaction: once the number of species increases, they have a strong influence on
the physical environment. The mechanism of the modification of the environment
through the influence of living organism in it, is known as reaction. Most of the
changes occurs in soil, water, light condition etc.
5) Stabilization: It is the final stage of succession process, where more or less stable
community called climax formed which is in equilibrium with the environment.
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:
Phytoplankton stage: These are the pioneer community. Mainly blue green
algae, green algae, diatoms and bacteria etc.
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.
Hydrosere: different stage of plant growth
3) 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.
4) 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.
5) 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.
6) Woodland stage: As the marsh land disappear soil become more dry and give rise
to vegetation like shrubs( Salix, cornus) and trees ( populus, Alnus).
7) 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
2) Lithosere: A Xerosere on Rock: It start with bare rock and culminate into a forest
stage. Different stages of Lithosere are as follows:
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.
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.
Moss stage : Xerophytic mosses such as Tortula, Grimmia appears after lichens
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.
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
Forests are formed by a community of plants which is predominantly structurally
defined by its trees, shrubs, climbers and ground cover.
Natural vegetation looks vastly different from a group of planted trees, which are
in orderly rows. The most ‘natural’ undisturbed forests are located mainly in our
National Parks and Wildlife Sanctuaries.
Each forest type forms a habitat for a specific community of animals that are
adapted to live in it.
Forest ecosystem has two component:
a) abiotic aspects: Include soil type, rainfall pattern in the forest are, light pattern,
water amount, temperature condition.
b) biotic aspects: The plants and animals form communities that are specific to each
Plants include the trees, shrubs, climbers, grasses, and herbs in the forest.
Animal include the species of mammals, birds, reptiles, amphibians, fish, insects and
other invertebrates and a variety of microscopic animals.
Forest types in India
They can also be classified according to the nature of their tree species – evergreen,
deciduous, xerophytic or thorn trees, mangroves, etc.
They can also be classified according to the most abundant species of trees such as
Sal or Teak forests.
In many cases a forest is named after the first three or four most abundant tree
grow in the Himalayan mountain region, where the temperatures are low.
These forests have tall trees with needlelike leaves and downward sloping branches
so that the snow can slip off the branches.
have cones instead of seeds
Trees- Pine, deodar
Animals- Wild goats and sheep, Snow leopard, Himalayan black bear,
High rainfall areas of the Western Ghats, North Eastern India and the Andaman and
There is no dry leafless phase as in a deciduous forest. An evergreen forest looks
green throughout the year. Thus very little light penetrates down to forest floor. The
forest abounds in animal life and is most rich in insect life.
Trees- Jamun, Ficus, Dipterocarpus
Animals- Tiger, Leopard, Sambar
are found in regions with a moderate amount of seasonal
Rainfall. Teak tree is one of the dominant tree species in these type of forest
The deciduous trees shed their leaves during the winter and hot summer months.
In March or April they regain their fresh leaves just before the monsoon, when
they grow vigorously in response to the rains.
Thus there are periods of leaf fall and canopy regrowth. The forest frequently has
a thick undergrowth as light can penetrate easily onto the forest floor.
Trees- Teak, Sal Animals- Tiger, Chital, Deer,
Thorn forests are found in the semi- arid regions of India.
The trees, which are sparsely distributed, are surrounded by open grassy
Thorn forest trees have long or fibrous roots to reach water at great depths.
These have thorns to reduce water loss through evapotranspiration.
Trees- Babul, Ber, Neem Animals - Blackbuck, Chinkara, Wolf,
grow along the coast especially in the river deltas.
These plants are able to grow in a mix of saline and fresh water.
The mangrove trees have breathing roots that emerge from the
Trees- Avicenia, Rhizophora Animals- Crocodile, fish, shorebirds – sandpipers
Importance of Forests resource:
Aesthetic and cultural values.
Problem associated with the forest resource and its conservation.
rainfall is usually low and/or the soil depth and quality is poor.
The low rainfall prevents the growth of a large number of trees and shrubs,
but is sufficient to support the growth of grass cover during the monsoon.
Grassland shows seasonal variation with low productivity during summer
and high productivity during rainy
A variety of grasses, herbs, and several species of insects, birds and mammals
have evolved so that they are adapted to these wide-open grass covered
areas. These animals are able to live in conditions where food is plentiful
after the rains, so that they can store this as fat that they use during the dry
period when there is very little to eat.
Man began to use these grasslands as pastures to feed his livestock
Grassland Types in India:
The Himalayan pasture belt extends up to the snowline. The grasslands at a lower
level form patches along with coniferous or broadleaved forests
The animals migrate up into the high altitude grasslands in summer and move
down into the forest in winter when the snow covers the grassland.
These Himalayan pastures have a large variety of grasses and herbs. Himalayan hill
slopes are covered with thousands of colorful flowering plants. There are also a
large number of medicinal plants.
Extends as a belt south of the Himalayan foothills
Terai consists of patches of tall grasslands interspersed with a Sal forest
The patches of tall elephant grass, which grows to a height of about 5m,
are located in low-lying waterlogged areas.
Scrublands of the Deccan Plateau:
Semi-arid plains of Western India, Central India and the Deccan - covered by
grassland tracts with patches of thorn forest.
Several mammals such as the wolf, the blackbuck, the chinkara, and birds such as
floricans are adapted to these arid conditions.
The Scrublands of the Deccan Plateau are covered with seasonal grasses and herbs
on which its fauna is dependent.
The Shola grasslands consist of patches on hillslopes along with the Shola
forests on the Western Ghats, Nilgiri and Annamalai ranges.
This forms a patchwork of grassland on the slopes and forest habitats along the
streams and low-lying areas.
Grasslands are not restricted only to low rainfall areas. Certain grassland
types form when clearings are made in different forest types.
The grasslands are related to repeated fires that do not permit the forest to
Some grass and herb species are more sensitive to excessive grazing and are
suppressed if the area is over grazed.
Others are destroyed by repeated fires and cannot regenerate. Thus overused or
frequently burnt grasslands are degraded and are poor in plant species diversity.
Important of Grassland:
Pasture land 4) habitat for diverse species of insects.
Grass is also used to thatch houses and farm sheds.
Threats to grassland ecosystem:
Over utilization and changes in land use of the ‘common grazing lands’ of rural
communities has lead to their degradation. Extinction of their species- Cheetah,
A major threat to natural grasslands is the conversion of grasslands into irrigated
farmlands. In the Deccan, grasslands have been altered to irrigated farms and are
now mainly used to grow sugarcane.
How can grassland ecosystems be conserved?
Grasslands should not be overgrazed and areas of the grasslands should be either
closed for grazing or rotational grazing pattern is established.
Fires must be prevented and rapidly controlled. In hilly areas soil and water
management in each micro-catchments helps grasslands to return to a natural
highly productive ecosystem.
To protect the most natural undisturbed grassland ecosystems, Sanctuaries and
National Parks must be created. Their management should focus on preserving all
their unique species of plants and animals.
Desert and semi arid lands are highly specialised and sensitive
ecosystems that are easily destroyed by human activities.
The species of these dry areas can live only in this specialised habitat.
Desert ecosystem in India:
Deserts and semi arid areas are located in Western India and the Deccan Plateau.
The climate in these vast tracts is extremely dry. There are also cold deserts such as
in Ladakh, which are located in the high plateaus of the Himalayas.
The most typical desert landscape that is seen in Rajasthan is in the Thar Desert.
This has sand dunes. There are also areas covered with sparse grasses and a few
shrubs, which grow if it rains.
In most areas of the Thar, the rainfall is scanty and sporadic. In an area it may rain
only once every few years.
In the adjoining semi arid tract the vegetation consists of a few shrubs and thorny
trees such as kher and babul
The Great and Little Rann of Kutch are highly specialized arid ecosystems. In the
summers they are similar to a desert landscape.
However as these are low-lying areas near the sea, they get converted to salt
marshes during the monsoons.
During this period they attract an high number of aquatic birds such as ducks,
geese, cranes, storks, etc.
Desert and semi arid regions have a number of highly specialized insects and
reptiles. The rare animals include the Indian wolf, desert cat, desert fox and birds
such as The Great Indian Bustard and the Florican.
Some of the commoner birds include partridges, quails and sandgrouse.
How are desert and semi-arid ecosystems used?
Areas of scanty vegetation with semi-arid scrubland have been used for camel,
cattle and goat grazing in Rajasthan and Gujarat.
Areas that have a little moisture, have been used for growing crops such as jowar,
The natural grasses and local varieties of crops have adapted to growing at very
low moisture levels. These can be used for genetic engineering and developing arid
land crops for the future.
What are the threats to desert ecosystems?
Conversion of these lands through extensive irrigation systems has changed several
of the natural characteristics of this region. The canal water evaporates rapidly
bringing the salts to the surface. The region becomes highly unproductive as it
becomes saline. Example: The Indira Gandhi Canal
Pulling excessive groundwater from tube wells lowers the water table creating an
even drier environment.
How can desert ecosystems be conserved?
Desert ecosystems are extremely sensitive. Their ecological balance that forms a
habitat for their plants and animals is easily disturbed.
Desert people have traditionally protected their little water resources. The Bishnois
in Rajasthan are known to have protected their Khejdi trees and the blackbuck
antelope for several generations.
There is an urgent need to protect residual patches of this ecosystem within
National Parks and Wildlife Sanctuaries in desert and semi arid areas.
The Pond ecosystem
The pond is the simplest aquatic ecosystem to observe.
There are differences in a pond that is temporary and has water only in the
monsoon, and a lake that is an aquatic ecosystem throughout the year.
Most ponds become dry after the rains are over and are covered by
terrestrial plants for the rest of the year.
When a pond begins to fill during the rains, its life forms such as the algae and
microscopic animals, aquatic insects, snails, and worms come out of the floor
of the pond where they have remained dormant in the dry phase.
Gradually more complex animals such as crabs frogs and fish return to the
pond. The vegetation in the water consists of floating weeds and rooted
vegetation on the periphery which grow on the muddy floor under water and
emerge out of the surface of the water.
As the pond fills in the monsoon a large number of food chains are
Algae is eaten by microscopic animals, which are in turn eaten
by small fish on which larger carnivorous fish depend. These are in turn
eaten by birds such as kingfishers, herons and birds of prey.
Aquatic insects, worms and snails feed on the waste material excreted by
animals and the dead or decaying plant and animal matter.
The temporary ponds begin to dry after the rains and the surrounding
grasses and terrestrial plants spread into the moist mud that is exposed.
Animals such as frogs, snails and worms remain dormant in the mud,
awaiting the next monsoon.
( High productivity)
Lakes are big fresh water bodies with standing water. They are divided into shallow
water zone called Littoral zone, an open water zone where effective penetration of
solar light takes place called Limnetic zone and deep profundal zone with no
penetration of light.
Lakes shows thermal stratification during the summer period: Epilimnion( warm
surface layer) and Hypolimnion ( Cold, bottom layer). In between there is
thermocline( region of sharp drop in temperature).
Lakes can be Oligotrophic (low nutrient concentration), mesotrophic and
eutrophic( high nutrient concentration especially nitrogen and phosphate)
River ecosystem: It’s a lotic ecosystem, where water flow downward from mountain
highland and flowing through the plain fall in the sea. River ecosystem have two type
of production: autochthonous( production within the stream) and allochthonous( supplied
from terrestrial sources).
Ocean have two major life zone:
1) Costal zone: relatively warm, nutrient rich shallow water. Due to ample sunlight it
is zone of high productivity.
Open sea: It is deeper part of ocean away from the continental shelf. It is vertically
divided into three parts:
Euphotic zone: receive abundant sunlight and shows high photosynthetic
Bathyal zone: receive dim light and is zone of geological activity.
Abyssal zone: is the dark zone( 2000 to 5000 meter deep), however it support
world’s largest ecological unit.
Estuary ecosystem: It is partially enclosed coastal area at the mouth of river where
fresh water and salty sea water meet. Therefore organism present in in estuaries
shows wide range of tolerance for temperature and salinity. Such organism are
known as eurythermal and euryhaline.
Estuaries have a rich biodiversity and many of the species are endemic.
How are aquatic ecosystems used?
clean freshwater on which his life is completely dependent and for other
Water is essential for agriculture
Marshes and wetlands are of great economic importance for people who
live on their fish, crustacea, reeds, grasses and other produce.
What are the threats to aquatic ecosystems?
Water pollution occurs from sewage and poorly managed solid waste in urban
areas when it enters the aquatic ecosystem of lakes and rivers.
Sewage leads to a process called eutrophication, which destroys life in the water
as the oxygen content is severely reduced.
Beside domestic waste addition of industrial waste results into metal pollution,
which is dangerous for both aquatic biota and human life.
How can aquatic ecosystems be conserved?
Water pollution must be prevented.
Aquatic ecosystems, especially wetlands, need protection by including
them in Sanctuaries or National Parks in the same way in which we
protect natural forests.
Construction of dam and barrage should be avoided to maintain the
natural flow of river system.