Every animal is a link in the food chain and a repository of a particular genome. The food chains are built up in such a way that there is a
biological control at every step. If the chain is broken, the biological control is lifted resulting in large scale disturbance and destruction of foodweb. For example, President Roosevalt of U.S.A. ordered killing of carnivores of
a national park so that deer could live peacefully. However, within a
decade, the national park changed into a desert with no deer.