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Just as the systems within an organism combine and interact to form a larger system, so too do these individual living things combine to form a larger, ecological system. And just as something unpleasant on the surface--like pain--can alert the larger system to a potentially life-threatening condition, so too do ecological systems maintain the balance necessary for their survival with using negative feedback loops.
One example of these feedback loops in operation is the food chain. Because animals higher on the food chain depend on the availability of their prey in adequate proportions to survive, if something happens to alter these proportions unfavorably (for example, a high birth rate among the predator species or an epidemic among the prey) the stability of the ecosystem falls into jeopardy and negative feedback loops are triggered.
Ecological systems can restore this equilibrium in several ways. First, members of the predator species will begin to have difficulty getting enough food. This will trigger their negative feedback loops--perhaps causing members of that species to move on in search of more plentiful prey--or perhaps causing some to perish from starvation.
The ecosystem will may be responding from the other direction as well: the prey species that has now become relatively scarce is also the predator species for some organism lower on the food chain. Left unfettered by decimation of its predator species, the population of this lower organism is likely to explode. This creates ideal conditions for surviving predators to thrive and reproduce, or even for new predators to move in--and soon the balance of nature is restored.
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