Predator-Prey Relationships

In a predator-prey relationship, the population sizes of the predator and the prey are linked, and they often rise and fall in regular cycles.The cycle works like this:1. When there are many prey, predators have plenty of food, so more predators survive and reproduce and the predator population increases.
2. More predators eat more prey, so the prey population decreases.
3. With less food available, predators compete more; more starve and fewer reproduce, so the predator population decreases.
4. With fewer predators, more prey survive and reproduce, so the prey population increases again, and the cycle repeats.The peaks in the predator population lag behind the peaks in the prey population, because it takes time for extra food to be turned into more predator offspring. The predator population is also usually smaller than the prey population, because energy is lost at each trophic level.A classic example is the snowshoe hare and the Canada lynx, whose numbers (from fur-trapping records) rose and fell in cycles of about 10 years. Studies later showed that the hare's own food supply and disease also affected hare numbers, so predator-prey cycles are rarely controlled by predation alone.In laboratory experiments, predator and prey populations often both die out, because the prey have nowhere to hide. In natural habitats, refuges allow some prey to survive, which keeps the cycle going.