Food Chain and Food web

Food Chain and Food web

The formation and transfer of food energy in the ecosystem takes place from one level to the next in a hierarchical manner. The levels through which food energy passes from one group of organisms to the other group are called tropic levels.

The chain of transformation and transfer, of food energy in the ecosystem from one group of organism to the other group through a series of steps or levels (trophic levels) is called food chain.

In other words, the chain of transfer of food energy form one group of organisms to the other group in the biosphere (ecosystem) is called food chain and the point where food energy is transferred from one group of organisms to the other group is called trophic level.

On an average there are four trophic levels but they can vary from 2,3 to even 5, 6 etc depending on the length of food chain or size and scale of ecosystem we take into account.

Trophic Level- 1: This is the base of food chain where autotrophic primary producers like green plants produce food from nutrients, CO₂ and water by the process of photosynthesis. Sunlight is the primary source of energy entering the ecosystem.

Thus green plants transform solar energy into food energy entering the ecosystem.

Thus green plants transform solar energy into food energy or chemical energy, which is stored by green plants to develop their tissues. Some portion of this energy is lost through respiration, while some other portion is transferred form trophic level one to next trophic levels when herbivores or omnivores eat the plants.

Trophic Level – 2: It includes herbivores. These constitute primary consumers. They do not produce food on their own but depend on autotrophy for food e.g. grazers like goat, rabbit, etc.

Trophic Level- 3: The animals which depend on herbivore animals for food are included in trophic level 3. They are called carnivores as well as secondary consumers.

Trophic Level – 4: The animals which derive their food from all the three lower trophic levels are included in trophic level 4 e.g. man. These animals are called as omnivores. Decomposers too drive their energy from all the trophic levels.

Thus food chain is the sequence of energy transfer from one trophic level to the next one. A food chain may be linear e.g. crops- food grains – mouse – snake- hawk.

A food chain may also be complex involving many interconnected and overlapping food chains. This happens when greater number of species feed on many kinds of prey. Such complicated food chain is called a food web. For example, plants produce grains which are eaten by mouse. Mouse is eaten by snakes, cats, and mongoose. Mongoose itself eats snakes. Similarly insects feeding on animals ‘bloods are eaten by frogs while frogs themselves are eaten by snakes and mongoose. The prey birds like hawk, eagles and vultures too are dependent on population of these small animals. On the other hand grass and plants are eaten by goats which are eaten by wolves, leopards and tigers and man. Plants in turn are dependent on birds, butterflies, squirrel, man etc for seed dispersal. Thus in a food web large number of organisms are dependent on a multitude of organisms for their survival. If population of any one of the species is increased or decreased with respect to carrying capacity of the region, then survival of the whole food chain is risked. When an ecosystem has large number of species and prey base, it becomes resilient to changes in population of a particular species, as alternative food is also available .A  complex food chain is an indicator of large and well developed biodiversity.