Environmental homeostasis, or balance, is maintained via an elaborate network of negative-feedback loops. A negative-feedback loop is a system in which the output of one cycle reduces or reverses the input of the next cycle. These processes tend to drive complex systems toward a stable equilibrium.
An example of negative feedback that helps to maintain the balance of nature is found in predator/prey ratios. When the population of prey animals expands, the food available to predators is more abundant. The environment then supports an expansion of the population of predators, who then consume more prey and reduce the population to a sustainable level. This reduction in prey populations then forces a commensurate drop in predator numbers.