Food Chains UPSC

The biotic factors of the ecosystem are linked together by food. For example, the producers form the food for the herbivores; the herbivores form the food for the carnivores. 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 the transfer 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
  • Phytoplanktons ° Copepod ° Herring


This chain begins 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.

  • Detritivores are an important aspect of many ecosystems. They can live on any type of soil with an organic component, including marine ecosystems, where they are termed interchangeably with bottom feeders.
  • Typical detritivorous animals include millipedes, springtails, woodlice, dung flies, slugs, many terrestrial worms, sea stars, sea cucumbers, fiddler crabs, and some sedentary polychaetes such as worms of the family Terebellidae.
  • Leaf litter ° Earthworm ° Blackbird
  • Dead animal ° Blowfly maggots ° Frog ° Hawk
  • Dead animal ° Earthworm ° Frog ° Snake ° Hawk


The various 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.

                                                      Threats in the Food Chain


Food webs are very important in maintaining the stability of an ecosystem. For example, the deleterious growth of grasses in a grass land is controlled by the herbivores. When one type of herbivore becomes extinct, the other types of herbivores increase in number and control the vegetation. Similarly, when one types of herbivorous animal becomes extinct, the carnivore predating of this type may eat another type of herbivore. Thus, the existence of a food web denotes the self-sustaining capacity of an ecosystem. Some species, if eliminatedseriously affect the ecosystem. These are called keystone species.   

Marine food web

  • Compared to terrestrial environments, marine environments have biomass pyramids which are inverted at the base. In particular, the biomass of consumers (copepods, krill, shrimp, forage fish) is larger than the biomass of primary producers. This happens because the ocean’s primary producers are tiny phytoplankton which grow and reproduce rapidly, so a small mass can have a fast rate of primary production. In contrast, many significant terrestrial primary producers, such as mature forests, grow and reproduce slowly, so a much larger mass is needed to achieve the same rate of primary production.
  • Because of this inversion, it is the zooplankton that make up most of the marine animal biomass. As primary consumers, zooplankton are the crucial link between the primary producers (mainly phytoplankton) and the rest of the marine food web (secondary consumers).
  • Primary producers: At the base of the ocean food web are single-celled algae and other plant-like organisms known as phytoplankton. Like plants on land, phytoplankton use chlorophyll and other light-harvesting pigments to carry out photosynthesis, absorbing atmospheric carbon dioxide to produce sugars for fuel.  Among the phytoplankton are members from a phylum of bacteria called cyanobacteria. Marine cyanobacteria include the smallest known photosynthetic organisms. 
  • The most important groups of phytoplankton include the diatoms and dinoflagellates. Diatoms are especially important in oceans, where according to some estimates they contribute up to 45% of the total ocean’s primary production. Diatoms are usually microscopic, although some species can reach up to 2 millimetres in length.