Predation is one of nature's ways of controlling population size. Without predatore, certain species of prey would grow too numerous. They would use up resources and perhaps drive other organisms to extinction. When prey animals are plentiful, predator populations increase. They reduce the prey population and reduce their own availablev food as a result. If the predatore don't have enough food, some die or leave the area. Thus, the predator population decreases. This allows the prey population to begin to grow again. Population changes are cyclical.