2. Ecosystem – Components and Classification, Ecotone, Functions of Ecosystem UPSC Notes | EduRev

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An ecosystem is defined as a structural and functional unit of biosphere consisting of community of living beings and the physical environment, both interacting and exchanging materials between them. It includes plants, trees, animals, fish, birds, micro‐organisms, water, soil, and people. When an ecosystem is healthy (i.e. sustainable) it means that all the elements live in balance and are capable of reproducing themselves


Components of Ecosystem

The components of the ecosystem is categorised into abiotic of non‐living and biotic of living components. Both the components of ecosystem and environment are same.


1. Abiotic Components

the inorganic and non‐living parts of the world. consists of soil, water, air, and light energy etc. involves a ,large number of chemicals like oxygen, nitrogen‐, etc. and physical processes including volcanoes, earthquakes, floods, forest fires, climates, and weather conditions. Abiotic factors are the most important determinants of where and how well an organism exists in its environment. Although these factors interact with each other, one single factor can‐limit the range of an organism.

a) Energy

Energy from the sun is essential for maintenance of life. Energy determines the distribution of organisms in the environment.

b) Rainfall

c) Temperature :Temperature is a critical factor of the environment which greatly influences survival of organisms. Organisms can tolerate only a certain range of temperature and humidity.

d) Atmosphere :It is made up of 21% oxygen, 78% nitrogen , 0.038% carbon dioxide and other inert gases (0.93% Argon, Neon etc).

e) Substratum :Land is covered by soil and a wide variety of microbes, protozoa, fungi and small animals (invertebrates) thrive in it

f) Materials:

(i) Organic compound

Such as proteins, carbohydrates, lipids, humic substances are formed from inorganic compound on decomposition.

(ii) Inorganic compound

Such as carbon, carbon dioxide, water, sulphur, nitrates, phosphates, and ions of various metals are essential for organisms to survive.

g) Latitude and altitude

Latitude has a strong influence on an area's temperature, resulting in change of climates such as polar, tropical, and temperate. These climates determine different natural biomes. From sea level to highest peaks, wild life is influenced by altitude. As the altitude increases, the air becomes colder and drier, affecting wild life accordingly.( wild life decrease as altitude increase)


2. Biotic Components :Biotic components include living organisms comprising plants, animals and microbes and are classified according to their functional attributes into producers and consumers.

a) Primary producers ‐ Autotrophs (self‐nourishing) Primary producers are basically green plants (and certain bacteria and algae). They synthesise carbohydrate from simple inorganic raw materials like carbon dioxide and water in the presence of sunlight by the process of photosynthesis for themselves, and supply indirectly to other non‐ producers. In terrestrial ecosystem, producers are basically herbaceous and woody plants, while in aquatic ecosystem producers are various species of microscopic algae.

b) Consumers — Heterotrophs or phagotrophs (other nourishing) Consumers are incapable of producing their own food (photosynthesis). They depend on organic food derived from plants, animals or both.

Consumers can be divided into two broad groups

(i) Macro consumers‐ 

They feed on plants or animals or both and are categorised on the basis of their food sources.

Herbivores are primary consumers which feed mainly on plants e.g. cow, rabbit.

Secondary consumers feed on primary consumers e.g. wolves.

Carnivores which feed on secondary consumers are called tertiary consumers e.g. lions which can eat wolves.

Omnivores are organisms which consume both plants and animals e.g. man.

(ii) Micro consumers ‐ Saprotrophs (decomposers or osmotrophs)

They are bacteria and fungi which obtain energy and nutrients by decomposing dead organic substances (detritus) of plant and animal origin. The products of decomposition such as inorganic nutrients which are released in the ecosystem are reused by producers and thus recycled.

Earthworm and certain soil organisms (such as nematodes, and arthropods) are detritus feeders and help in the decomposition of organic matter and are called detrivores.


Classification of Eco‐system

1. Natural Ecosystem‐

Terrestrial‐ Forests, Grasslands, Deserts

Aquatic‐ Fresh Waters, Saline Waters, Marine Waters


Ecotone :‐ a zone of junction between two or more diverse ecosystems. For e.g. the mangrove forests represent an ecotone between marine and terrestrial ecosystem.

Characteristics of Ecotone

It may be very narrow or quite wide. It has the conditions intermediate to the adjacent ecosystems. Hence it is a zone of tension.

It is linear as it shows progressive increase in species composition of one in coming community and a simultaneous decrease in species of the other out going adjoining community.

A well developed ecotones contain some organisms which are entirely different from that of the adjoining communities. Sometimes the number of species and the population density of some of the species is much greater in this zone than either community. This is called edge effect For example the density of birds is greater in the mixed habitat of the ecotone between the forest and the desert.



a description of all the biological, physical and chemical factors that a species needs to survive, stay healthy and reproduce. No two species have exact identical niches. Niche plays an important role in conservation of organisms.

Types of Niche

1. Habitat niche ‐ where it lives

2. Food niche ‐ what is eats or decomposes & what species it competes with

3. Reproductive niche ‐how and when it reproduces.

4. Physical & chemical niche ‐ temperature, land shape, land slope, humidity & other requirement.



The terrestrial part of the biosphere is divisible into enormous regions called biomes, which are characterized, by climate, vegetation, animal life and general soil type.

No two biomes are alike.

The most important climatic factors are temperature and precipitation.

1. Tundra‐ Northern most region adjoining the ice bound poles. Devoid of trees except stunted shrubs in the southern part of tundra biome, ground flora includes lichen, mosses and sedges.

The typical animals are reindeer, arctic fox polar bear, snowy owl, lemming, arctic hare, ptarmigan. Reptiles and amphibians are almost absent

2. Taiga‐ Northern Europe, Asia and North America. Moderate temperature than tundra. Also known as boreal forest.

The dominating vegetation is coniferous evergreen mostly spruce, with some pine and firs. The fauna consists of small seed eating birds, hawks, fur bearing carnivores, little mink, elks, puma, Siberian tiger, wolverine, wolves etc.

3. Temperate Deciduous Forest‐ Extends over Central and Southern Europe, Eastern North America, Western China, Japan, New Zealand etc.

Moderate average temperature and abundant rainfall. These are generally the most productive agricultural areas of the earth The flora includes trees like beech, oak, maple and cherry. Most animals are the familiar vertebrates and invertebrates.

4. Tropical rain forest‐ Tropical areas in the equatorial regions, which is a bound with life. Temperature and rainfall high.

Tropical rainforest covers about 7% of the earth's surface & 40% of the world's plant and animal species.

Multiple storey of broad‐leafed evergreen tree species are in abundance.

Most animals and epiphytic plants(An epiphyte is a plant that grows harmlessly upon another plant) are concentrated in the canopy or tree top zones

5. Savannah‐ Tropical region: Savannah is most extensive in Africa Grasses with scattered trees and fire resisting thorny shrubs.

The fauna include a great diversity of grazers and browsers such as antelopes, buffaloes, zebras, elephants and rhinoceros; the carnivores include lion, cheetah, hyena; and mongoose, and many rodents

6. Grassland‐ North America, Ukraine, etc . Dominated by grasses. Temperate conditions with rather low rainfall. Grasses dominate the vegetation. The fauna include large herbivores like bison, antelope, cattle, rodents, prairie dog, wolves, and a rich and diverse array of ground nesting bird

7. Desert‐ Continental interiors with very low and sporadic rainfall with low humidity. The days are very hot but nights are cold. The flora is drought resistance vegetation such as cactus, euphorbias, sagebrush. Fauna : Reptiles, Mammals and birds.


Aquatic Zones

Aquatic systems are not called biomes,

The major differences between the various aquatic zones are due to salinity, levels of dissolved nutrients; water temperature, depth of sunlight penetration.

1. Fresh Water Ecosystem‐Fresh water ecosystem are classified as lotic (moving water) or lentic (still or stagnant water).

2. Marine Ecosystem‐

3. Estuaries‐Coastal bays, river mouths and tidal marshes form the estuaries. In estuaries, fresh water from rivers meet ocean water and the two are mixed by action of tides. Estuaries are highly productive as compared to the adjacent river or sea



a part of the earth where life can exist.

represents a highly integrated and interacting zone comprising of atmosphere (air), hydrosphere (water) and lithosphere (land)

Life in the biosphere is abundant between 200 metres (660 feet) below the surface of the ocean and about 6,000 metres (20,000 feet) above sea level.

absent at extremes of the North and South poles.

Living organisms are not uniformly distributed throughout the biosphere



ENERGY FLOW‐ Energy is the basic force responsible for all metabolic activities. The flow of energy from producer to top consumers is called energy flow which is unidirectional.

Energy flows through the trophic levels: from producers to subsequent trophic levels. There is a loss of some energy in the form of unusable heat at each trophic level.

The trophic level interaction involves three concepts namely :‐

1. Food Chain

2. Food Web

3. Ecological Pyramids


1. FOOD CHAIN‐ A food chain starts with producers and ends with top carnivores. The sequence of eaten and being eaten, produces transfer of food energy and it is known as food chain.

Grazing food chain‐The consumers which start the food chain, utilising the plant or plant part as their food, constitute the grazing food chain.

This food chain begins from green plants at the base and the primary consumer is herbivore

For example, In terestrial ecosystem, grass is eaten up by caterpillar, which is eaten by lizard and lizard is eaten by snake.

In Aquatic ecosystem phytoplanktons (primary producers) is eaten by zoo planktons which is eaten by fishes and fishes are eaten by pelicans

Detritus food chain‐ The food chain starts from dead organic matter of decaying animals and plant bodies to the micro‐organisms and then to detritus feeding organism called detrivores or decomposer and to other predators.

Litter —■Earthworms —■Chicken—■Hawk

Detritus food chain

The distinction between these two food chains is the source of energy for the first level consumers.



"A food web illustrates, all possible transfers of energy and nutrients among the organisms in an ecosystem, whereas a food chain traces only one pathway of the food".



The steps of trophic levels expressed in a diagrammatic way are referred as ecological pyramids.

The food producer forms the base of the pyramid and the top carnivore forms the tip. Other consumer trophic levels are in between.

The pyramid consists of a number of horizontal bars depicting specific trophic levels which are arranged sequentially from primary producer level through herbivore, carnivore onwards. The length of each bar represents the total number of individuals at each trophic level in an ecosystem.

The ecological pyramids are of three categories

1.Pyramid of numbers,

2.Pyramid of biomass, and

3.Pyramid of energy or productivity


1. Pyramid of Numbers

This deals with the relationship between the numbers of primary producers and consumers of different levels. Depending upon the size and biomass, the pyramid of numbers may not always be upright, and may even be completely inverted.

(a) Pyramid of numbers ‐ upright

In this pyramid, the number of individuals is decreased from lower level to higher trophic level.

This type of pyramid can be seen in grassland ecosystem.

(b) Pyramid of numbers ‐ inverted

In this pyramid, the number of individuals is increased from lower level to higher trophic level.

A count in a forest would have a small number of large producers, for e.g. few number of big trees. This is because the tree (primary producer) being few in number and would represent the base of the pyramid and the dependent herbivores (Example ‐ Birds) in the next higher trophic level and it is followed by parasites in the next trophic level. Hyper parasites being at higher trophic level represents higher in number.

A pyramid of numbers does not take into account the fact that the size of organisms being counted in each trophic level can vary

the pyramid of number does not completely define the trophic structure for an ecosystem.


2. Pyramid of Biomass

In this approach individuals in each trophic level are weighed instead of being counted. This gives us a pyramid of biomass, i.e., the total dry weight of all organisms at each trophic level at a particular time.

Biomass is measured in g/m2.

(a) Upward ‐pyramid: For most ecosystems on land, the pyramid of biomass has a large base of primary producers with a smaller trophic level perched on top

(b) Inverted pyramid‐In contrast, in many aquatic ecosystems, the pyramid of biomass may assume an inverted form


3. Pyramid of Energy

To compare the functional roles of the trophic levels in an ecosystem, an energy pyramid is most suitable.

An energy pyramid, reflects the laws of thermodynamics, with conversion of solar energy to chemical energy and heat energy at each trophic level and with loss of energy being depicted at each transfer to another trophic level.

Hence the pyramid is always upward, with a large energy base at the bottom.

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