In an ecosystem everything is related to everything else. The component species are maintained by a complex set of interactions among the enumerable life forms as well as between the life forms and the abiotic factors of the environment. Extinction of a component species, therefore, results in a chain of events affecting a number of other species adversely.
Those fonts which are obligately dependent on the extinct species have to die out. There are several instances of animals starving to death following the disappearance of species which constituted their mail source of food. The chain of events following near extinction of genus Hibiscadelphus which resulted in disappearance of many Hawaiian honey creepers and its pollinators has been well illustrated (Diamond 1989). Extinction of each tropical plant species leads to a loss of about 10-30 species of insects because many tropical insect species are highly specialized in their feeding habits and behaviour (Peter H. Raven 1976).
Some workers notably Paine (1966), Terborgh (1986), have coined the term ‘Key-stone species’ to distinguish those species which influence the ability of a number of other species to survive in a community. Some of these Key-stone species, like top predators which often control herbivore populations, may be quite conspicuous. Others may not be so.
A large number of inconspicuous plant species possess specialized set of insect fauna. Their disappearance leads to disappearance of those insect species as well. Naturally Key-stone species in a community should be accorded top priority in conservation efforts because their loss entails a loss of other species as well.