Predation

Predation is when one animal (the predator) kills and eats another (the prey). It is a biotic factor that affects the size of both populations.In a simple system where a predator depends mainly on one prey species, the populations often rise and fall in regular cycles:
• When prey are plentiful, predators have plenty of food, survive and breed well, so the predator population increases.
• More predators eat more prey, so the prey population falls.
• With less food, fewer predators survive and breed, so the predator population falls.
• With fewer predators, more prey survive, so the prey population rises again, and the cycle repeats.The predator peak comes after the prey peak, because it takes time for the predators to breed in response to the extra food. The predator population is also usually smaller than the prey population, because energy is lost between trophic levels.A famous example is the snowshoe hare and the lynx in Canada, whose numbers (from fur-trapping records) cycled about every 10 years. In reality these cycles are also affected by other factors, such as the hares' food supply and disease, so predation is rarely the only cause.Predation also acts as a selection pressure. Prey evolve camouflage, speed, warning colours and group behaviour; predators evolve better senses and hunting strategies.Worked example. If the prey population peaks in year 4 and again in year 14, the cycle length is 14 − 4 = 10 years.