Function of Ecosystem – Food Chain & Food Web


  • The function of an ecosystem is a broad, vast and complete dynamic system. It can be studied under the following three heads.
    • Energy flow
    • Nutrient cycling (biogeochemical cycles)
    • Ecological succession or ecosystem development


  • 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.

Trophic level interactionENERGY FLOW, Food Chain, Food Web, Trophic Levels, Various levels of Trophics, Difference Between Food Chain and Food Web, Trophic level interaction, Producers, Consumers, Types of Biotic Interaction, Complete Environment and Ecology Notes for competitive exams for free...

    • A trophic level is the representation of energy flow in an ecosystem.
    • The trophic level of an organism is the position it occupies in a food chain.
    • The levels through which food energy passes from one group of organism to the other group are called trophic levels.
    • Trophic level interaction deals with how the members of an ecosystem are connected based on nutritional needs.
    • Trophic levels are numbered according to the steps an organism is away from the source of food or energy, which is the producer (plants).
    • Energy always flows from lower (producer) to higher (herbivore, carnivore etc.) trophic level.
    • Energy level decreases from the first trophic level upwards due to loss of energy in the form of heat at each trophic level.
    • This energy loss at each trophic level is quite significant. Hence there are usually not more than four-five trophic levels (beyond this the energy available is negligible to support an organism).
    • The trophic level interaction involves three concepts namely
      • Food Chain
      • Food Web
      • Ecological Pyramids

Trophic levels

Autotrophs Green plants (Producers)
Heterotrophs Herbivore (Primary consumers)
Heterotrophs Carnivores (Secondary consumers)
Heterotrophs Carnivore (Tertiary consumers)
Heterotrophs Top carnivores (Quaternary consumers)



Autotrophs or Producers
  • This category includes all those organisms, green plants, bacteria and algae which are capable of converting solar energy into chemical energy and storing foodstuff in the presence of carbon dioxide and water.
Heterotrophs or Consumers
  • All other organisms are consumers which cannot convert solar energy into food.
  • Heterotrophs utilise, and decompose the complex material produced by autotrophs.
  • Depending upon the feeding habits, the heterotrophs are classified as follows:
    1. Primary Consumers: Organisms or animals which feed on green plants (autotrophs) to obtain energy for survival are the primary consumers. They are also known as herbivores. Cows, buffaloes, goats, horses, rabbits, insects and grasshoppers are some of the examples of primary consumers.
    2. Secondary Consumers: Animals which feed on herbivores are known as secondary consumers. For example, frogs, lizards, which eat grasshoppers and other insects.
    3. Tertiary Consumers: Tertiary consumers are those that eat the flesh of secondary consumers. For example tiger, lion, leopard, vultures. Since they are not killed and eaten by other animals, they are known as top carnivores.
Decomposers or Saprophytes
  • The dead bodies of the producers and consumers are eaten and broken down into simple inorganic substance by certain microbes (bacteria and fungi). They are known as decomposers or saprophytes. The decomposers play a vital role of releasing essential materials from the dead matter and thus maintain a continuous cycle of energy flow and of materials.


  • The chain of transformation and transfer of food energy in the ecosystem from one group of organism to another group through a series of steps or levels is called food chain.
  • Transfer of food energy from green plants (producers) through a series of organisms with repeated eating and being eaten link is called a food chain.

E.g. Grasses → Grasshopper → Frog → Snake → Hawk/Eagle.

  • Each step in the food chain is called trophic level.
  • A food chain starts with producers and ends with top carnivores.
  • The trophic level of an organism is the position it occupies in a food chain.

ENERGY FLOW, Food Chain, Food Web, Difference Between Food Chain and Food Web, Trophic level interaction, Producers, Consumers, Types of Biotic Interaction, Complete Environment and Ecology Notes for competitive exams for free...

Types of Food Chains

    • Grazing food chain
    • Detritus food chain

Grazing food chain

      • The consumers which start the food chain, utilising the plant or plant part as their food and ends with carnivores as consumers at the last level, with the herbivores being at the intermediate level, constitute the grazing food chain.
      • There is a loss of energy at each level which may be through respiration, excretion or decomposition.
      • For example, in a terrestrial ecosystem, the grass is eaten by a caterpillar, which is eaten by lizard and lizard is eaten by a snake.
      • In Aquatic ecosystem phytoplankton (primary producers) are eaten by zooplanktons which are eaten by fishes and fishes are eaten by pelicans.

Detritus food chain

      • This type of food chain starts from organic matter of dead and decaying animals and plant bodies consumed by the micro-organisms.
      • Dead organic matter or detritus feeding organisms are called detrivores or decomposers.
      • The detrivores are eaten by predators.
      • In an aquatic ecosystem, the grazing food chain is the major conduit for energy flow.
      • As against this, in a terrestrial ecosystem, a much larger fraction of energy flows through the detritus food chain than through the grazing food chain.

ENERGY FLOW, Food Chain, Food Web, Difference Between Food Chain and Food Web, Trophic level interaction, Producers, Consumers, Types of Biotic Interaction


  • When the feeding relationships in a natural ecosystem become more complicated, the food chain becomes complicated. This complicated situation develops when greater number of species feed on many kinds of prey. Such a complicated food chain is known as food web.
  • “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”.
  • Food web represents all the possible paths of energy flow in an ecosystem.
  • If any of the intermediate food chains is removed, the succeeding links of the chain will be affected largely.
  • The food web provides more than one alternative for food to most of the organisms in an ecosystem and therefore increases their chance of survival.

Difference Between Food Chain & Food Web

Difference Between Food Chain & Food Web


Organisms living in this earth are interlinked to each other in one way or other. The interaction between the organisms is fundamental for its survival and functioning of ecosystem as a whole.

Types of biotic interaction


      • Both species benefits from one another.
      • When similar interaction occurs within a species, it is known as cooperation.
      • Eg. – Bacteria Rhizobium, which is found at the root nodules of a leguminous plant is an example of the Mutualism. In this relationship, the plant supplies the water, mineral, food to the bacterium while Rhizobium fixes the atmospheric nitrogen which is used by the plant.


      • One species benefits, the other is unaffected.
      • Eg. – Sea anemone and the Clown Fish. The Fish gets shelter in the sea anemone.


      • There is no net benefit or harm to either species.


      • One species is harmed, the other is unaffected.
      • Eg. – A large tree inhibits the growth of small plants laying nearby due to its shades, while small plants have no effect on the large tree.


      • One species benefits, the other is harmed.
      • Although the predator may or may not kill its prey, the act of predation and often results in the death of its prey and the tissues of the prey are eventually consumed by the predator.
      • Eg. – Interaction between Wolf and a Rabbit.


      • One species benefits, the other is harmed.
      • The parasites are the organism which depends on other organism for their nutrition, respiration etc.
      • Eg. – Ticks, lice and mites are external parasites while tapeworm, roundworm etc. are an example of internal parasites. In case of Plants, Amer bel is a good example.


      • Both species are harmed by the interaction.
      • Both the species compete with each other for the resources like food, shelter, mating, and both the species get harmed out of the process of competition.
      • Competition leads to the elimination of the less fit or the weaker species from the ecosystem.
      • Eg. – Competition between Trees, Shrubs etc. in Rain Forest for Nutrient, Sunlight etc.


So, this was all about the post on Function of Ecosystem – Food Chain & Food Web.

In the Next Post (Click Here), we will discuss about the Functions of Ecosystem – Ecological Pyramids.

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