food chain

Food chain  

Concept:

The transfer of food from plant sources through a series of organisms form a chain called food chain.

Ex: phytoplankton àzooplanktonà small fishà large fishà man

The above food chain is observed in the Indian rivers.

Ex:  grasshopperà melanopusà bufoà a rattle snake

This food chain occurs in Indian pasture

The above two examples clearly show that the base of the food chain is formed by plant( autotrophs) which are grazed by herbivore; which are predated by carnivores; which may be further predated by another higher carnivores.

Food chain relationships are very complex, as one organism may act as a food source of many other organisms and so on. For ex: grass may be eaten by cattle, grasshopper, rabbits, etc…….each of these may be eaten various other carnivores such as snake, toads, birds, or hyenas.

Thus instead of a simple food chain a complex web like structure called food web exists in the environment. Thus plant occupies the first trophic level called producers. The plant grazers occupy the second position called the primary consumers. The flesh eaters are at the third position called secondary consumers. The next trophic level is called tertiary consumer………the different trophic level are arranged in form of a pyramid.

Charles Elton the distinguished British ecologist realized in 1927 that there must be a limit to the number of links in any food chain. He surveyed many ecosystems and concluded that number of trophic levels very rarely exceeds five because during energy transfer loss of energy takes place in form of heat.

Charles Elton suggested that a small ecosystem cannot have many tertiary consumers because only a small amount of energy reaches the top trophic level.

Types of food chain:

In nature three types of food chain operates in general.

1.   Grazing food chain: the food chain which is herbivore based and the herbivores are considered important consumers is called grazing food chain. Ex: food chain found in the grasslands and the aquatic ecosystems. In grass land ecosystem or the aquatic ecosystem usually up to 50% of primary production is grazed upon by the herbivores and the remaining 50% are consumed by the decomposers as dead organic matter.

2.   Detritus food chain: in a forest ecosystem the insects are usually the dominant primary consumers but they consume less than 10% of the net primary production and the rest 90% of the total food is later on is fed by the small detritus feeding animals such as oligochaetes, and other micro organisms such as protozoa etc…….the animals consume the food by digesting it partially or fully making organic materials available for bacterial and fungal attack. The microorganisms also act as food for other animals. This type of food chain is called detritus food chain.

3.   Parasitic food chain: There must be a limit to he direst grazing of the producers. Because there out grazing may deplete or reduce their productivity therefore besides the food chain a parasitic food chain may also operate in many ecosystem, although the energy passing may be negligible. A parasitic food chain involves a HOST-PARASITE-HYPERPARASITE KINKS.