Predation acts to increase growth rate by thinning the density of prey populations, which releases survivors from competition. At the same time, predators intimidate prey into decreasing their feeding activity and increasing refuge use, causing prey to grow more slowly. Predation often greatly reduces prey population density and alters community composition and species diversity. Competition when there aren’t enough resources to go around and different organisms fight to get them. Predation is a kind of competition where a predator hunts and eats its prey. These are biotic factors, which mean they come from living things and can affect the size of a population. In predation, one organism kills and consumes another. Predation provides energy to prolong the life and promote the reproduction of the organism that does the killing, the predator, to the detriment of the organism being consumed, the prey. Avoidance behavior thus generally promotes coexistence if prey partition resources but not predators, whereas it undermines coexistence if prey partition predators but not resources. Predators keep the prey population under control. The prey species could achieve very high population densities and cause ecosystem instability in the absence of predators. Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species. With no predators to control the population and alter feeding behavior, the prey species quickly degrade and over-run its habitat. As food becomes scarce, the population becomes sick and malnourished, and will either move or crash. Generally the answer is that without predators to suppress their number, prey outstrip available food resources, nesting sites, or some other limited resource and thus begin to suppress their further growth through competition. Too many predators and not enough prey leads to predators starving and dying because they can't find enough food. Too many prey and not enough predators leads to the spread of disease and depletion of resources for the prey species and others that live in their habitat.Predator-prey cycles are based on a feeding relationship between two species: if the prey species rapidly multiplies, the number of predators increases until the predators eventually eat so many prey that the prey population dwindles again. Soon afterwards, predator numbers likewise decrease due to starvation. When predators are scarce, prey rises in numbers. As their source of food increases, predators rise in abundance. When there are enough predators, prey numbers decline. With a scarcity of food, the number of predators crashes and the cycle repeats.