The great poet Nikolay Zabolotsky there are the following lines:
Bug eat grass, bug bite bird,
Eagle drank the brain of the bird's head...
This is a very accurate description of the food chain. It is a series of sequential relations that occur in the ecosystem between predators and their victims.
Green plants are the primary producers of organic matter. They serve as food for animals, fungi, some microorganisms are the primary consumers, which, in turn, eaten by secondary consumers (predators. Thus, build the chain: grass -- herbivores-predators.
The chain can be shorter or longer.
For example, grass -- hare-wolf - short chain, and pine -- aphids -- ladybug -- spider garden spider -- cuckoo-hawk - long chain.
The ratio of certain types of the same food chain can be visualized as a pyramid of biomass. Moreover, the biomass of predators is much smaller than the grass biomass, and biomass of herbivorous occupies an intermediate position. Thus in nature remains an equilibrium when we have enough food.
Now imagine that people exterminated wolves. The result will immensely raspadatsya herbivores and will quickly eat up all the grass, and then, they will begin to die from hunger. This environmental catastrophe known. In his time in Australia, where there was virtually no predators were released imported from Europe rabbits. Rodents began to multiply very quickly and soon became a real disaster for farmers. With long-eared had to fight every conceivable way up to the fence in the fields of barbed wire, through which an electrical current was passed.
This example proves once again how important it is to maintain a balance in the food chain.