Che 110
Che 110
Che 110
The ecosystem is the structural and functional unit of ecology where the living organisms
interact with each other and the surrounding environment. In other words, an ecosystem is
a chain of interaction between organisms and their environment. The term “Ecosystem”
was first coined by A.G.Tansley, an English botanist, in 1935.
Definition: The living community of plants and animals in any area together with the non-
living components of the environment such as soil, air and water, constitute the ecosystem.
Some ecosystems are equally vigorous and are less affected by a certain level of human
disturbance. Others are highly fragile and are quickly destroyed by human activities.
Mountain ecosystems are extremely fragile as degradation of forest cover leads to severe
erosion of soil and changes in river courses. Island ecosystems are easily affected by any
form of human activity which can lead to the rapid extinction of several of their unique
species of plants and animals. Evergreen forests and coral reefs are also examples of
species rich fragile ecosystems which must be protected against a variety of human
activities that lead to their degradation. River and wetland ecosystems can be seriously
affected by pollution and changes in surrounding land use
Structure of the Ecosystem
The structure of an ecosystem is
characterised by the organisation of both
biotic and abiotic components. This
includes the distribution of energy in our
environment. It also includes the climatic
conditions prevailing in that particular
environment.
The structure of an ecosystem can be split
into two main components, namely:
➢ Biotic Components
➢ Abiotic Components
The biotic and abiotic components are
interrelated in an ecosystem. It is an open
system where the energy and components
can flow throughout the boundaries.
3.1.1 Understanding ecosystems
Functional aspects:
1) Energy cycles.
2) Food chains.
3) Diversity-interlinkages between organisms.
4) Nutrient cycles-biogeochemical cycles.
5) Evolution.
Every living organism is in some way dependent on other organisms. Plants are food for
herbivorous animals which are in turn food for carnivorous animals. Thus there are
different tropic levels in the ecosystem. Some organisms such as fungi live only on dead
material and inorganic matter.
Plants are the ‘producers’ in
producers the ecosystem as they
manufacture their food by using
energy from the sun. In the forest
these form communities of plant life.
In the sea these include tiny algal
forms to large seaweed. The
herbivorous animals herbivorous
animals are primary consumers as
they live on the producers. In a
forest, these are the insects,
amphibia, reptiles, birds and
mammals. The herbivorous animals
include for example hare, deer and
elephants that live on plant life. They
graze on grass or feed on the foliage from trees. In grasslands, there are herbivores such as
the blackbuck that feed on grass. In the semiarid areas, there are species such as the
chinkara or Indian gazelle. In the sea, there are small fish that live on algae and other plants.
At a higher tropic level, there are carnivorous animals, or animals secondary
consumers, which live on herbivorous animals. In our forests, the carnivorous animals are
tigers, leopards, jackals, foxes and small wild cats. In the sea, carnivorous fish live on other
fish and marine animals. Animals that live in the sea range in size from microscopic forms
to giant mammals such as the whale.
Decomposers or detrivores Decomposers or detrivores are a group of organisms
consisting of small animals like worms, insects, bacteria and fungi, which break down dead
organic material into smaller particles and finally into simpler substances that are used by
plants as nutrition. Decomposition thus is a vital function in nature, as without this, all the
nutrients would be tied up in dead matter and no new life could be produced Most
ecosystems are highly complex and consist of an extremely large number of individuals of
a wide variety of species. In the species-rich tropical ecosystems (such as in our country),
only a few species are very common, while most species have relatively few individuals.
Some species of plants and animals are extremely rare and may occur only at a few
locations. These are said to be ‘endemic’ to these areas.
When human activities alter the balance in these ecosystems, the “perturbation”
leads to the disappearance of these uncommon species. When this happens to an endemic
species that is not widely distributed, it becomes extinct for all time.
3.4 ENERGY FLOW IN THE ECOSYSTEM
Every ecosystem has numerous interconnected
mechanisms that affect human life. These are the
water cycle, the carbon cycle, the oxygen cycle, the
nitrogen cycle and the energy cycle. While every
ecosystem is controlled by these cycles, in each
ecosystem its abiotic and biotic features are distinct
from each other. All the functions of the ecosystem
are in some way related to the growth and
regeneration of its plant and animal species. These
linked processes can be depicted as the various
cycles. These processes depend on energy from sunlight. During photosynthesis carbon
dioxide is taken up by plants and oxygen is released. Animals depend on this oxygen for
their respiration. The water cycle depends on the rainfall, which is necessary for plants and
animals to live. The energy cycle recycles nutrients into the soil on which plant life grows.
Our own lives are closely linked to the proper functioning of these cycles of life. If human
activities go on altering them, humanity cannot survive on our earth
3.4.1 The Water Cycle
The water (or hydrologic) cycle shows the movement of water through different
reservoirs, which include oceans, atmosphere, glaciers, groundwater, lakes, rivers, and
biosphere. Solar energy and gravity drive the motion of water in the water cycle. Simply
put, the water cycle involves water moving from oceans, rivers, and lakes to the atmosphere
by evaporation, forming clouds. From clouds, it falls as precipitation (rain and snow) on
both water and land. The water on land can either return to the ocean by surface runoff,
rivers, glaciers, and subsurface groundwater flow, or return to the atmosphere by
evaporation or transpiration (loss of water by plants to the atmosphere).
An important part of the water cycle is how water varies in salinity, which is the
abundance of dissolved ions in water. The saltwater in the oceans is highly saline, with
about 35,000 mg of dissolved ions per liter of seawater. Evaporation (where water
changes from liquid to gas at ambient temperatures) is a distillation process that produces
nearly pure water with almost no dissolved ions. As water vaporizes, it leaves the dissolved
ions in the original liquid phase. Eventually, condensation (where water changes from gas
to liquid) forms clouds and sometimes precipitation (rain and snow). After rainwater falls
onto land, it dissolves minerals in rock and soil, which increases its salinity. Most lakes,
rivers, and near-surface groundwater have a relatively low salinity and are called
freshwater. The next several sections discuss important parts of the water cycle relative to
fresh water resources.
The energy cycle is based on the flow of energy through the ecosystem. Energy from
sunlight is converted by plants themselves into growing new plant material which includes
leaves, flowers, fruit, branches, trunks and roots of plants.
Since plants can grow by converting the sun’s energy directly into their tissues,
they are known as producers in producers the ecosystem. The plants are used by
herbivorous animals as herbivorous animals food, which gives them energy. A large part
of this energy is used up for day to day functions of these animals such as breathing,
digesting food, supporting growth of tissues, maintaining blood flow and body
temperature. Energy is also used for activities such as looking for food, finding shelter,
breeding and bringing up young ones. The carnivores in carnivores turn depend on
herbivorous animals on which they feed. Thus the different plant and animal species are
linked to one another through food chains. food chains Each food chain has three or four
links. However as each plant or animal can be linked to several other plants or animals
through many different linkages, these inter-linked chains can be depicted as a complex
food web. food web This is thus called the ‘web of life’ that shows that there are thousands
of interrelationships in nature. The energy in the ecosystem can be depicted in the form of
a food pyramid food pyramid or food pyramid energy pyramid. The food energy pyramid
has a large base of plants called ‘- producers’. The pyramid has a narrower middle section
that depicts the number and biomass of herbivorous animals, herbivorous animals which
are called ‘first order consumers’. first order consumers The apex depicts the small biomass
of carnivorous animals called ‘second order second order consumers’. Man is one of the
animals at the apex of the pyramid. Thus to support mankind, there must be a large base of
herbivorous animals and an even greater quantity of plant material.
When plants and animals die, this material is returned to the soil after being broken
down into simpler substances by decomposers such as insects, worms, bacteria and fungi
so that plants can absorb the nutrients through their roots. Animals excrete waste products
after digesting food, which goes back to the soil. This links the energy cycle to the Nitrogen
cycle.
These cycles are a part of global life processes. These biogeochcemical cycles have
specific features in each of the ecosystems. These cycles are however linked to those of
adjacent ecosystems. Their characteristics are specific to the plant and animal communities
in the region. This is related to the geographical features of the area, the climate and the
chemical composition of the soil. Together the cycles are responsible for maintaining life
on earth. If mankind disturbs these cycles beyond the limits that nature can sustain, they
will eventually break down and lead to a degraded earth on which man will not be able to
survive.
Man
Goat
Grass
3.7 INTRODUCTION, TYPES, CHARACTERISTIC FEATURES, STRUCTURE
Terrestrial Food Pyramid
Aquatic
AND FUNCTION Food Pyramid
Types of Ecosystem
An ecosystem can be as small as an oasis in a desert, or as big as an ocean, spanning
thousands of miles. There are two types of ecosystem:
• Terrestrial Ecosystem
• Aquatic Ecosystem
Terrestrial Ecosystems
Terrestrial ecosystems are exclusively land-based ecosystems.
Terrestrial ecosystems Terrestrial ecosystems in Terrestrial ecosystems their
natural state are found in different types of forests, grasslands, semiarid areas, deserts and
sea coasts. Where the land is intensively used, these have been gradually modified over
several thousand years into agricultural and pastoral regions. In the recent past they have
been rapidly converted into intensively irrigated agricultural ecosystems or into urban and
industrial centers.
“Though this has increased production of food and pro- has increased
production of food and provides the raw material for ‘consumer’ goods that we use, the
overuse and misuse of land and natural ecosystems has led to a serious degradation of
our environment. degradation of our environment.”
When our human population was small, most ecosystems could supply all our
needs. Resources were thus used ‘sustainably’. sustainably’. As industrial ‘development’
led to a very great increase in consumption of resources, the short term economic gains for
people became an indicator of progress, rather than long term ecological benefits. This has
resulted in an ‘unsustainable of natural resources. Forests thus disappear, rivers run dry,
deserts begin to spread, and air, water and soil become increasingly polluted as by-products
of development. Human well being itself is then seriously affected.
There are different types of terrestrial ecosystems distributed around various geological
zones. They are as follows:
1. Forest Ecosystems
2. Grassland Ecosystems
3. Tundra Ecosystems
4. Desert Ecosystem
Forest Ecosystem
A forest ecosystem consists of several plants, animals and microorganisms that live in
coordination with the abiotic factors of the environment. Forests help in maintaining the
temperature of the earth and are the major carbon sink.
Coniferous forest Broadleaved forest Evergreen forest
Forest types in India: The forest type depends upon the abiotic factors such as climate and
soil characteristics of a region. Forests in India can be broadly divided into Coniferous
forests and Broadleaved forests.
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.
Coniferous forests grow in the Himalayan mountain region, where the temperatures are
low. These forests have tall stately trees with needlelike leaves and downward sloping
branches so that the snow can slip off the branches. They have cones instead of seeds and
are called gymnosperms.
Broadleaved forests have several types, such as evergreen forests, deciduous forests, thorn
forests, and mangrove forests. Broadleaved forests have large leaves of various shapes.
Evergreen forests grow in the high rainfall areas of the Western Ghats, North Eastern India
and the Andaman and Nicobar Islands. These forests grow in areas where the monsoon
lasts for several months. Some even get two monsoons, such as in Southern India.
Evergreen plants shed a few of their leaves throughout the year. There is no dry leafless
phase as in a deciduous forest. An evergreen forest thus looks green throughout the year.
The trees overlap with each other to form a continuous canopy. Thus, very little light
penetrates down to the forest floor. Only a few shade loving plants can grow in the ground
layer in areas where some light filters down from the closed canopy. The forest is rich in
orchids and ferns. The barks of the trees are covered in moss. The forest abounds in animal
life and is most rich in insect life.
Deciduous forests are found in regions with a moderate amount of seasonal rainfall that
lasts for only a few months. Most of the forests in which Teak trees grow are of this type.
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.
Thorn forests are found in the semi-arid regions of India. The trees, which are sparsely
distributed, are surrounded by open grassy areas. Thorny plants are called xerophytic
species and are able to conserve water. Some of these trees have small leaves, while other
species have thick, waxy leaves to reduce water losses during transpiration. Thorn forest
trees have long or fibrous roots to reach water at great depths. Many of these plants have
thorns, which reduce water loss and protect them from herbivores.
Mangrove forests grow along the coast especially in the river deltas. These plants are able
to grow in a mix of saline and fresh water. They grow luxuriantly in muddy areas covered
with silt that the rivers have brought down. The mangrove trees have breathing roots that
emerge from the mudbanks.
Forest utilisation: Natural forests provide local people with a variety of products if the
forest is used carefully. Over-exploitation for fuel wood or timber, and conversion to
monoculture plantations for timber or other products, impoverishes local people as the
economic benefit goes to people who live elsewhere. The entire resource base on which
local people have traditionally survived for generations, is rapidly destroyed. Eventually
the forest is completely degraded. Natural forest ecosystems play an important role in
controlling local climate and water regimes. It is well-known that under the canopy of a
natural forest, it is cooler than outside the forest During the monsoon, the forest retains
moisture and slowly releases it through perennial streams during the rest of the year.
Plantations fail to perform this function adequately. The loss of forest cover in the
catchments of a river thus leads to irreversible changes such as excessive soil erosion, large
run-off of surface water during monsoons leading to flash floods, and a shortage of water
once the monsoons are over.
Forest products that are collected by Forest products people include food such as fruit,
roots, herbs and medicinal plants. People depend on fuelwood to cook food, collect fodder
for domestic animals, cut building material for housing, collect medicinal plants that have
been known for generations for several ailments and use a variety of non timer forest
products such as fiber, cane, gum, to make household articles. Wood from different species
of trees have special uses. For instance a soft wood is used for the yok of a bullock cart
while a very hard wood is used for its axil. These forest products are of great economic
value as they are collected, sold and marketed. Forest dwellers and agricultural people use
these goods directly. Other people get them indirectly from the market. Traditional types
of agriculture needs forest material such as branches and leaves, which are burnt to form
wood ash which acts as a fertiliser for crops such as rice. Urban people use these forest
resources indirectly as all their food and other goods come from agricultural areas that are
dependent on the neighbouring forests.
Forest services include the control of the flow services of water in streams and rivers.
Forest cover reduces surface runoff of rainwater and allows ground water to be stored.
Forests prevent erosion of soil. Once soil is lost by erosion, it can take thousands of years
to reform. Forests regulate local temperature. It is cooler and more moist under the shade
of the trees in the forest. Most importantly, forests absorb carbon dioxide and release
oxygen that we breathe. The wild relatives of our crop plants and fruit trees have special
characteristics in their genes which are used to develop new crops and newer varieties of
fruit. These newer varieties developed from wild relatives give greater yields of are more
resistant to diseases. New industrial products are being produced from the wild plants of
the forest. Many of our new medicines come from wild plants.
Direct uses of forest products: Fruits – mango, jamun, awla Roots – Dioscoria Medicine
– Gloriosa, Foxglove Fuelwood – many species of trees and shrubs Small timber for
building huts and houses Wood for farm implements Bamboo and cane for baskets Grass
for grazing and stall feeding livestock
Indirect uses of forest products: Building material for construction and furniture for the
urban sector Medicinal products collected and processed into drugs Gums and resins
processed into a variety of products Raw material for industrial products and chemicals
Paper from bamboo and softwoods.
What are the threats to the forest ecosystem?
As forests grow very slowly, we cannot use more resources than they can produce
during a growing season. If timber is felled beyond a certain limit the forest cannot
regenerate. The gaps in the forest change the habitat quality for its animals. The more
sensitive species cannot survive under these changed conditions. Wood is illegally
extracted from many forests leading to a highly disturbed ecosystem.
As the forest resources are exploited beyond what they can produce the forest
canopy is opened up, the ecosystem is degraded, and its wildlife is seriously threatened. As
the forest is fragmented into small patches its wild plant and animal species become extinct.
These can never be brought back. Extinction is forever.
What if the forests disappear?
When forests are cut down tribal people who depend directly on them for food and
fuelwood and other products find it very difficult to survive. Agricultural people do not get
enough fuelwood, small timber, etc. for making houses and farm implements. Urban people
who depend on food from agricultural areas, which in turn depend on neighbouring forest
ecosystems have to pay a higher price for food as human population grows. Insects that
live and breed in the forest such as bees, butterflies and moths decrease in abundance once
forests are degraded. The rain that falls on deforested land flows directly into nearby rivers.
Thus, water is not retained under the ground. People thus do not get a sufficient quantity
of water throughout the year. The exposed soil is rapidly washed away during the rains
once the protective forest cover is removed. Thus, agriculture is seriously affected in such
areas. In deforested areas, the water in streams is brown in colour as soil is washed away
while water in forested streams is crystal clear. Wild animals lose their habitat. This leads
to extinction of our precious species. Residual forests must be protected from being
destroyed any further if all the diverse species of plants and animals are to be kept for future
generations.
How can forest ecosystems be conserved?
We can conserve forests only if we use its resources cautiously. This can be done by using
alternate sources of energy instead of fuelwood. There is a need to grow more trees than
are cut down from forests every year for timber. Afforestation needs to be done
continuously from which fuelwood and timber can be judiciously used. The natural forests
with all their diverse species must be protected as National Parks and Wildlife Sanctuaries
where all the plants and animals can be preserved.
3.7.2 Grassland ecosystems
Grassland Ecosystem
In a grassland ecosystem, the vegetation is dominated by grasses and herbs. Temperate
grasslands, savanna grasslands are some of the examples of grassland ecosystems.
Grassland ecosystems are important mechanisms of ecological communities on Earth, and
perform key functions in carbon (C) cycling, climate regulation, and the maintenance of
biological diversity. However, since the middle of the 20th century, these ecosystems have
been subjected to major environmental fluctuations because of climate change and
strengthened human activities. These ongoing changes have affected grass growth and the
functioning of constituent ecosystem. In this context, net primary productivity (NPP) is
one key indicator that can be used to measure the ability of a grassland ecosystem to
maintain a level of sustainable development, recorded via the net amount of C captured by
land plants annually through photosynthesis. Variations in NPP are therefore indicative of
relationships between vegetation growth and the surrounding environment; it is therefore
critical to better understand the responses of grassland NPP to both climate change and
human activities.
Grassland Types in India:
Grasslands form a diversity of ecosystems that are situated in different climatic conditions
ranging from near desert conditions, to patches of shola grasslands that occur on hillslopes
alongside the extremely moist evergreen forests in South India. In the Himalayan
mountains there are the high cold Himalayan pastures. There are tracts of tall elephant
grass in the low-lying Terai belt south of the Himalayan foothills. There are semi-arid
grasslands in Western India, parts of Central India, and in the Deccan Plateau.
Semi-arid plains
Desert and semi arid lands are highly specialised and sensitive ecosystems that are easily
detroyed by human activities. The species of these dry areas can live only in this specialised
habitat.
What is a desert or a semi-arid ecosystem?
Deserts and semi arid areas are located in West ern 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 specialised
arid ecosystems. In the summers they are similar to a desert landscape.
How can desert ecosystems be conserved?
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 Indira Gandhi Canal in
Rajasthan is destroying this important natural arid ecosystem, as it will convert the region
into intensive agriculture. In Kutch, areas of the little Rann, which is the only home of the
Wild Ass, will be destroyed by the spread of salt works. Development Projects alter the
desert and arid landscape. There is a sharp reduction in the habitat available for its
specialised species bringing them to the verge of extinction. We need a sustainable form
of development that takes the special needs of the desert into account.
1. Freshwater Ecosystem
2. Marine Ecosystem
Freshwater Ecosystem
The freshwater ecosystem is an aquatic ecosystem that includes lakes, ponds, rivers,
streams and wetlands. These have no salt content in contrast with the marine ecosystem.
Wetlands are special ecosystems in which the water level fluctuates dramatically in
different seasons. They have expanses of shallow water with aquatic vegetation, which
forms an ideal habitat for fish, crustacea and water birds.
Marine Ecosystem
The marine ecosystem includes seas and oceans. These have a more substantial salt content
and greater biodiversity in comparison to the freshwater ecosystem.
Marine ecosystems are highly saline, while brackish areas have less saline water such as in
river deltas. Coral reefs are very rich in species and are found in only a few shallow tropical
seas. The richest coral reefs in India are around the Andaman and Nicobar islands and in
the gulf of Kutch. Brackish water ecosystems in river deltas are covered by mangrove
forests and are among the world’s most productive ecosystems in terms of biomass
production. The largest mangrove swamps are in the Sunderbans in the delta of the Ganges.
References:
1. env-book-FYBSc.pdf
2. https://opentextbc.ca/conceptsofbiologyopenstax/chapter/aquatic-and-marine-
biomes/
3. Textbook of Environmental Studies for Undergraduate Courses by Erach Bharucha
4. Fundamentals of Environmental Studies by Dr. Sarita Kumar, Sultan Chand
Publications.
5. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/ecosystem-
degradation
6. https://www.holidify.com/collections/forests-in-india
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UNIT-III-EXERCISE-ECOSYSTEM
Exercise
1. Ecosystem is smallest unit of__________
a) Ionosphere b) Lithosphere c) Biosphere d) Mesosphere
10. Identify the possible link “A” in the following food chain:
Plant Insect frog A Eagle
a) Cobra b) parrot c) rabbit d) wolf
14. The organisms which utilize plants and animals as food are called___________
a) Herbivores b) carnivores c) omnivores d) saprophytes
16. Food chain in which microorganisms breakdown the food formed by primary
producers is__________
a) Parasitic food chain b) detritus food chain
c)consumer food chain d) producer food chain
20. Which of the following chemical formula represents the nitrogen in the
atmosphere?
a) NH4 b) NO3 c) NO4 d) N2
23. The organisms which convert complex organic components of dead bodies into
simple organic molecules are called_______
a) Microorganisms b) decomposers c) transformers d) converters
30. Which process in the nitrogen cycle turns ammonium into nitrates?
a) Fixation b) nitrification c) assimilation d) ammonification
32. Through which process do living organisms release carbon into the
atmosphere?
a) Photosynthesis b) cellular respiration
c) transpiration d) combustion
33. Which cycle most likely includes sunlight, photosynthesis and respiration?
a) Water cycle b) carbon cycle c) oxygen cycle d) nitrogen cycle
35. Which of the following ecosystems has highest gross primary productivity?
41. Which state in India has the maximum percentage of its area covered by forest?
a) Arunachal Pradesh b) Madhya Pradesh
c) Mizoram d) Nagaland
44. According to the survey done by Ministry of Environment and Forest, the total
forest cover in India is around:
a) 33% b) 23% c) 21% d) 28%