In an ecosystem energy flows from one trophic level to another. A trophic level represents a group of organisms, which are either predators or they get consumed. All organisms in an ecosystem are linked to one another based on their nutritional needs. This relation between the individuals constitutes a linear chain called the food chain. Ultimately a food chain always begins with the producers. The various components of the food chain can be defined as a group of organisms in which there is transfer of food energy through a series of repeated eating and being eaten
Two types of food chains are recognized in nature. These are Grazing food chain and Detritous food chain.
Grazing food chain:
The grazing food chain starts from green plants passes on to herbivorous primary consumers and ends with carnivorous animals. Thus the nutrition produced by plants utilizing energy of solar radiation are used in the following three ways -
(i) Used for respiratory activity of the plant
(ii) Get decayed
(iii) May be consumed by herbivores
In a grazing food chain there are basically four trophic levies - Auto trophic, primary consumers, secondary consumers and tertiary consumers. Grazing food chain is the most important food chain in nature.
Detritous food chain:
Detritous or decomposing food chain begins with dead organic matter goes to micro organisms and then passes on to organisms that feed on detrivores (organisms that - eat detritus) and their predators. Ecosystems of this type are less dependent on direct solar energy. On the other hand they depend on the supply of organic matter produced by another ecosystem.
Detritus food chains are seen in those areas where there is plenty of organic matter in the soil as in temperate forests. In a detritous food chain organic matter to start the chain comes from outside. The main source of organic matter is the leaf fall from the trees producing lot of litter. The fallen leaf fragments are acted upon by saprophytic fungi and bacteria and are eaten by a small group of animals.
These animals include crabs, copepods, insect larvae, grass shrimps, nematodes etc. All these animals are called detritus consumers or detrivores. These animals are in-turn eaten by small fish. These small fish form food for large fish, fish eating birds constituting the large carnivores.