Food Chains and Food Webs

Food Chain:

• Ecosystems have an hierarchy of feeding relationships (trophic levels) that determine the pathway of energy flow in the ecosystem. The energy flow in the ecosystem can be illustrated as a Food chain.

• Sun is the ultimate source of energy in ecosystems. Producers or autotrophic organisms convert the solar energy into chemical or organic energy during photosynthesis. 

• This is the source of food for heterotrophic organisms and these animals may in turn be eaten by other animals. In this way energy is transferred through series of organisms. Such a sequence is called food chain or grazing link in the ecosystem. 

• Each stage of the food chain is known as a trophic level. Producers occupy the first trophic level. The second trophic level is occupied by the primary consumers and third is occupied by secondary consumers and so on.

• In some ecosystems, as much as 80% of primary production is not eaten by primary consumers. Instead, decomposer organisms consume plant materials. This type of food chain is konwn as detrital food chains, (eg. Tropical forest ecosystems).

Food Web:

• Food chains only illustrate a direct feeding relationship between one organism and another in a single hierarchy. 

• The reality though is very different. The diet of almost all consumers is not limited to a single food species. So a single species can appear in more than one food chain. (eg. Human, they feed on organisms of all trophic levels. They are called omnivores).

• The reality is that there is a complex network of interrelated food chains which is called a food web.