Food Chains and Food Webs

While studying the biotic components in an ecosystem we have realised that food prepared by green plants is consumed by a series of consumers, both herbivores and carnivores, and finally broken down into their elements and released back into nature by decomposers in nature. The nutritional sequence in which food is transferred from the plant (producer) through a series of organisms with repeated eating and being eaten is called a food chain. As food is being transferred from one organism to another a lot of energy from food is lost. Hence, the biggest food chain has four or five steps.

Illustrated below are some simple generalised food chains

Food chain in the forest

Food chain in grassland

Trophic levels in the food chains

The different steps or levels in a food chain form different trophic levels.

The illustration below is self-explanatory. This is the ecosystem that can exist on land.

Trophic levels

Thus a food chain of four levels is built up where green plants fix up the solar energy and prepare the food and make it, directly or indirectly, available for other consumers.

Significance of food chains

• The study of food chains helps in understanding food relationship and interdependence among various organisms in an ecosystem.

• The mechanism of transfer of food, energy and nutrients through various components of nature can also be studied

• The effect of the use of pesticides on the ecosystem can be studied. As several of them are not biodegradeable it goes on accumulating at every trophic level. Hence consumers at higher trophic levels will consume more poison along with their food. This phenomena is known as biological magnification.

• Indiscriminate use of DDT and other pesticides has an adverse effect on the food chain and consequently disturbs the ecosystem.