FUNCTIONS OF AN ECOSYSTEM



ENERGY FLOW : The flow of energy from producers to top consumers. It is unidirectional. To get an idea on the energy flow in an ecosystem we rely on trophic level interaction. It shows how members are connected based on nutritional needs. The feeding mechanism represented through trophic levels. Energy flows from lower to higher trophic levels. Loss of energy happens at each successive trophic level. Trophic level interaction deals with 3 concepts: Food Chain, Food Web and Ecological Pyramids.


The biotic factors of the ecosystem are linked together by food. The sequence of the eaters being eaten is called food chain.“Food chain is the sequence of who eats whom in a biological community (ecosystem) to obtain nutrition” or in another words thetransfer of energy in an ecosystem through a series of organisms, by eating and being eaten, constitutes food chains. The position of organisms in the food chain or each step of the food chain is referred as Trophic level.

There are two types of food chain.



This food chain starts from producers, passes through herbivores, then to carnivores and decomposers.

  • Grass ° Grass hopper ° Frog ° Snake ° Owl
  • Diatoms° Crustaceans ° Herrings


This chain starts with dead organic matter and ends up with inorganic compounds. There are certain organisms which depend exclusively on the dead bodies of animals and plants. These organisms are called detritivores.

  • Leaf litter ° Earthworm ° Blackbird
  • Dead animal ° Earthworm° Frog ° Snake ° Hawk


Food chains in an ecosystem are interconnected or interlinked with each other to form a network called food web. If the links in the chains that make up the web of life are disrupted due to human activities that lead to the loss or extinction of species, the web breaks down.









The graphical representation of the definite relationships between producers, consumers and decomposers with reference to their number, biomass and energy is known as ecological pyramids. Three different types of ecological pyramids are the pyramid of numbers, the pyramid of biomass and the pyramid of energy.



The number of organisms decreases from producer level to carnivore level. This is called pyramid of number. In most ecosystems the pyramid of number is mostly erect or upright eg. Grass land, but in some cases the pyramid of number is inverted. eg. Numerous insects live on a single huge tree. In this, number of individuals at the trophic level decreases from the producer level to the consumer level.


The biomass generally decreases from producer level to carnivore level. This is called pyramid of biomass. It is mostly upright or erect. eg. Fallow land. In aquatic ecosystem the pyramid of biomass is inverted. eg. The combined weight of phytoplankton in a lake is small as compared to weight of fish.



The amount of energy flow decreases from producer level to carnivore level, this is called pyramid of energy. The pyramid of energy is always erect or upright. It indicates the total energy at each trophic level of the food chain. It also exhibits that at each trophic level, loss of energy and material takes place, thus, at the producer level, the total energy available is relatively more than at the higher trophic levels.


The gradual and progressive replacement of one community by another, till the development of a stable community in that area (climax community), or a process through which ecosystems tend to change over a period of time is called as ecological succession. The stages in succession – where different communities predominate – are called seres. A community will eventually form which is in complete equilibrium with its physical environment and no further changes will occur to that community – this is then known as the climax community.



Primary succession occurs where there was no ecosystem before, beginning with a bare surface with no life or soil present. The bare surface may be rock from a recently erupted volcano or sand dunes or cliffs or even a lake surface.It starts with the arrival of living things such as lichens that do not need soil to survive. The first organisms to colonize the area are known as the pioneer species or community and usually consist of organisms such as algae and lichens.


Pioneer species: it is the first organism to colonize any newly available area and begin the process of ecological succession.


Climax community: A climax community is a mature, stable community that is the final stage of ecological succession. In an ecosystem with a climax community, the conditions continue to be suitable for all the members of the community, until another disturbance clears the area.eg. Pine trees in forest ecosystem.



They do not require soil. Lichens composed of two species, algae and fungi. The algae photosynthesize and the fungi absorb nutrients from rocks and holds water.  They are in symbiotic relationship. Over time, they break down the rock and the forces of weather and erosion help break down rocks into smaller pieces. When the lichens die, they accumulate in cracks. And they decompose, adding small amounts of organic matter to the rock to make soil. Simple plants like mosses and ferns can grow in the new soil. Hence when these simple plant die it add more organic material to the soil, leading to the creation of fertile soil. The fertile soil is made up of the broken rocks, decayed organisms, water, and air. By this the soil layer thickens, and grasses, wildflowers, and other plants begin to take over. Shrubs and trees can survive now. Insects, small birds, and mammals have begun to move in. What was once bare rock now supports a variety of life. Primary succession takes several hundred years to produce fertile soil naturally. Lichens are good pollution indicators.



It occurs on a surface where an ecosystem has previously existed, and that have beendisturbed or disrupted byanimals orhumans interference such as logging and clear-cutting, or by the result of natural disasters such as fires, floods, storms, earthquakes and volcanoes..Secondary succession begins in a place that already has soil and was once the home of living organisms. Occurs faster and has different pioneer species than primary succession.





An ecological niche is the functional role and position a species has in its environment and how it meets its needs for food and shelter, how it survives, and how it reproduces. A species niche includes all of its interactions with the biotic and abiotic factors of its environment.The abiotic or physical environment is also part of the niche because it influences how populations affect, and are affected by, resources and enemies .Niche is unique to each individual organism and no two species can have exactly the same ecological niches.



Method developed by the global footprint network for calculating the human impact on the nature. It is the impact of human activities measured in terms of the area of biologically productive land and water required to produce the goods consumed and to assimilate the wastes generated. Or it is the amount of the environment necessary to produce the goods and services necessary to support a particular lifestyle. It is the environmental input of a person or population.




An Ecotone is a transitional area of vegetation between two different ecosystems or plant communities, such as forest and grassland. The ecotone contains elements of both bordering communities as well as organisms which are characteristic and restricted to the ecotone. Ecotones are not limited to terrestrial communities; for example, the transition from soft bottom to hard bottom marine communities is an aquatic ecotone. Or Ecotones also appear where one body of water meets another (e.g., estuaries and lagoons).


Edge Effect: Ecotones often have a larger number of species and larger population densities than the communities on either side. This tendency for increased biodiversity within the ecotone is referred to as the “edge effect.” It is the influence of the two bordering communities on each other. These species are called Edge species.



Every animal species needs a certain amount of space to survive and thrive. The amount of space an animal uses on a regular basis is called its home range.It is the region that encompasses all the resources the animal requires to survive and reproduce. Home ranges can stretch for many miles or they can be only a few feet. The size of a home range often depends on the size of an animal.




For a given region, carrying capacity is the maximum number of individuals of a given species that an area’s resources can sustain indefinitely without significantly depleting or degrading those resources. This concept is expanded to include, not to degrade the cultural and social environment and not harming the physical environment in ways that could affect future generations. It’s a measure of sustainability with the changing conditions of environment


1.MUTUALISMBoth benefit

Eg : Lichens

2.COMMENSALISMOne benefits, other unaffected.

Eg: Birds in tree hollows

3.COMPETITIONBoth are harmed.

Eg: Competition b/w Cheetah and lion for food

4PREDATION AND PARASITISMOne benefits, other harmed.

Eg : Predation : big fish eating small fishes.  Parasitism : blood sucking by tick

5AMMENSALISM One is harmed, other unaffected.

Eg: cattle walking through grass.

6.NEUTRALISMNeither benefits nor harms either of the organisms.

Eg: Cactus and Tarantulas


Ecosystem one of the major governing entity of the environment.Everyone in the world depends completely on Earth’s ecosystems and the services they provide.

Over  years, humans have changed these ecosystems more rapidly and extensively than in any comparable period of time in human history.Thus, conservation and preservation of ecosystem should be a major concern to all. These problems, unless addressed, will substantially reduce the benefits that future generations obtain from ecosystems.



1.Which of the following statements best describes “carbon fertilization”?     (2018)

  • Increased plant growth due to increased concentration of carbon dioxide in the atmosphere
  • Increased temperature of Earth due to increased concentration of carbon dioxide in the atmosphere
  • Increased acidity of oceans as a result of increased concentration of carbon dioxide in the atmosphere
  • Adaptation of all living beings on Earth to the climate change brought about by the increased concentration of carbon dioxide in the atmosphere


2.The term “sixth mass extinction/sixth extinction” is often mentioned in the news in the context of the discussion of                                  (2018)

  • Widespread monoculture practices in agriculture and large-scale commercial farming with indiscriminate use of chemicals in many parts of the world that may result in the loss of good native ecosystems.
  • Fears of a possible collision of a meteorite with the Earth in the near future in the manner it happened 65 million years ago that caused the mass extinction of many species including those of dinosaurs. .
  • Large scale cultivation of genetically modified crops in many parts of the world and promoting their cultivation in other parts of the world which may cause the disappearance of good native crop plants and the loss of food biodiversity.
  • Mankind’s over-exploitation/misuse of natural resources, fragmentation/loss of natural habitats, destruction of ecosystems, pollution and global climate change.


3.Which one of the following is the best description of the term ‘ecosystem            (2015)

  • A community of organisms interacting with one another
  • That part of the Earth which is inhabited by living organisms
  • A community of organisms together with the environment in which they live
  • The flora and fauna of a geographical area


4.Which one of the following is the correct sequence of a food chain?            (2014)

  • Diatoms-Crustaceans-Herrings
  • Crustaceans-Diatoms-Herrings
  • Diatoms –Herrings-Crustaceans
  • Crustaceans-Herrings-Diatoms

5.Lichens, which are capable of initiating ecological succession even on a bare rock, are actually a symbiotic association of                               (2014)

(a) algae and bacteria                                                            (b) algae and fungi

(c) bacteria and fungi                                                            (d) fungi and mosses

6.Which one of the following is the process involved in photosynthesis?          (2014)

  • Potential energy is released to form free energy
  • Free energy is converted into potential energy and stored
  • Food is oxidized to release carbon dioxide and water
  • Oxygen is taken, and carbon dioxide and water vapour are given out

7.In the grasslands, trees do not replace the grasses as a part of an ecological succession because of                                                        (2013)

  • Insects and fungi
  • Limited sunlight and paucity of nutrients
  • Water limits and fire
  • None of the above

8.Which one of the following is the correct sequence of ecosystems in the order of decreasing productivity?                                                       (2013)

  • Oceans, lakes, grasslands, mangroves
  • Mangroves, oceans, grasslands, lakes
  • Mangroves, grasslands, lakes, oceans
  • Oceans, mangroves, lakes, grasslands

9.With reference to food chains in ecosystems, consider the following statements:                                                                                       (2013)

  1. A food chain illustrates the order in which a chain of organisms feed upon each other.
  2. Food chains are found within the populations of a species.
  3. A food chain illustrates the numbers of each organism which are eaten by others.

Which of the statements given above is/are correct?

(a) 1 only                      (b) 1 and 2 only               (c) 1, 2 and 3           (d) None

10.Which one of the following terms describes not only the physical space occupied by an organism, but also its functional role in the community of organisms?                                                                                    (2013)

(a) Ecotone                                   (b) Ecological niche

(c) Habitat                                            (d) Home range

11.With reference to the food chains in ecosystems, which of the following kinds of organism is/are known as decomposer organism/organisms?                                                                                   (2013)

  1. Virus Fungi           3. Bacteria

Select the correct answer using the codes given below:

(a) 1 only              (b) 2 and 3 only       (c) 1 and 3 only        (d) 1, 2 and 3

12.What would happen if phytoplankton of an ocean is completely destroyed for some reason?                                                               (2012)

  1. The ocean as a carbon sink would be adversely affected
  2. The food chains in the ocean would be adversely affected
  3. The density of ocean water would drastically decrease

Select the correct answer using the codes given below:

(a) 1 and 2 only    (b) 2 only         (c) 3 only          (d) 1, 2 and 3


13.In the context of ecosystem productivity, marine upwelling zones are important as they increase the marine productivity by bringing the                   (2011)

  1. Decomposer microorganisms to the surface
  2. Nutrients to the surface
  3. Bottom-dwelling organisms to the surface

Which of the statements given above is/are correct?

(a) 1 and 2             (b) 2 only     (c) 2 and 3       (d) 3 only






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