Environment - ECOSYSTEM (UPSC Environment notes)

Environment - ECOSYSTEM (UPSC Environment notes)
Posted on 14-02-2022


The ecosystem comprises of following components:

i. Components having a life which collectively is called biotic components. 

ii. Components which are non-living which collectively are called abiotic components. 

iii. Various conditions of existence like temperature, light, humidity, etc.


In an ecosystem, the biotic components can be further classified into the following categories:

i. Producers: It is the group of living organisms that is capable of producing their own food. 

ii. Consumers: It is a group of organisms that are dependent on producers or other consumers for their food. Those dependent on producers are known as primary consumers while those dependent on Primary consumers are called secondary consumers and so on. 

iii. Decomposers: These are microscopic organisms that act on dead and decaying matter to decompose them and derive energy in the process. 

In an ecosystem, the various biotic components can accordingly be arranged in trophic levels. Each trophic level is arranged according to food levels with producers at the bottom and higher-level consumers as we move up.

ecosystem environment upsc

The amount of living materials in each trophic level is known as the standing crop of that trophic level. The standing crop of a trophic level can be expressed in terms of a number of organisms or in terms of biomass. The joint representation of standing crops of these trophic levels is called Trophic Structure.

Trophic Structure also indicates the relationship between various biotic components of the ecosystem as the upper trophic level is dependent on the lower trophic levels for its survival. It can be represented by Ecological Pyramids. The trophic structure also indicates the transfer of energy from the lower trophic level to the upper trophic level in form of food.

Ecological Pyramids can be of three types:

i. Based on the number of organisms in each trophic level. 

ii. Based on the biomass of components of each trophic level. 

iii. Based on the energy content of each trophic level.


Pyramids based on numbers or on biomass may or may not be upright (i.e. they can be inverted depending on the nature of the ecosystem to which the pyramid belongs to). However, a pyramid based on energy is always upright. This indicates that while the number and mass of organisms may increase or decrease while moving from the bottom towards the apex in an ecological pyramid, the energy content always reduces from base to apex.


Ecological efficiency is the ratio of energy output from a trophic level to the energy input into that trophic level. Thus, it is efficiency with which organisms exploit their food and convert them into food for the next trophic level.

Assimilation efficiency is the efficiency with which the organisms at any trophic level utilize the input energy into that trophic level.


Very often the chemicals like pesticides enter into the food chain via producers. Many of these are neither digested nor excreted and they keep on accumulating in the body of consumers such that their concentration is higher in higher trophic levels as compared to lower trophic levels. This is called biological magnification. Large-scale deaths of vultures feeding on dead cattle occurred as large quantities of diclofenac that was present in cattle were poisonous for vultures.


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