Trophic Level

Each step or level of the food chain forms a trophic level.

•  The autotrophs or the producers are at the first trophic level. They fix up the solar energy and make it available for heterotrophs or the consumers.
•  The herbivores or the primary consumers come at the second.
•  The small carnivores or the secondary consumers are at the third trophic level.
•  The larger carnivores or the tertiary consumer form the fourth trophic level.

Trophic levels

Trophic levels

e.g. Food chain operating in the grassland, which is:

Grass → Insects → Frog → Birds

In this food chain, grass represents the 1st trophic level; insect represents the 2nd trophic level; frog represents the 3rd trophic level, whereas bird represents 4th trophic level.

Trophic levels in a food chain

CHARACTERISTICS OF A FOOD CHAIN:

In a food chain,

(a) There is repeated eating in which each group eats the smaller one and is eaten by the larger one. Thus, it involves a nutritive interaction between the biotic components of an ecosystem.

(b) The plants and animals which depend successively on one another form the limbs of a food chain.

(c) There is unidirectional flow of energy from sun to producers and then to a series of consumers of various types. Thus, a food chain is always straight and proceeds in a progressing straight line.

(d) Usually 80 to 90% of potential energy is lost as heat at each transfer on the basis of second law of thermodynamics (transformation of energy involves loss of unavailable energy).

(e) usually there are 4 or 5 trophic levels. Shorter food chains provide greater available energy and vice - versa.

(f) Omnivores occupy more than one trophic level and, some organisms occupy different trophic positions in different food chains.