These linkages are the prime movers of energy through food chains and are an important factor in the ecology of populations, determining mortality of prey and birth of new predators. Some simple systems do cycle, particularly those of the boreal forest and tundra, although this no longer seems the rule. Predator-prey systems are potentially unstable, as is seen in the lab where predators often extinguish their prey, and then starve. In nature, at least three factors are likely to promote stability and coexistence. Once predators decline, they prey can fuel a new round of population increase.
Prey evolve behaviors, armor, and other defenses that reduce their vulnerability to predators.
Alternative prey may provide a kind of refuge, because once a prey population becomes rare, predators may learn to search for a different prey species. Predation, while not the only cause of complex community interactions, has often been shown to have strong indirect effects and cascading effects. Predation also can be a strong agent of natural selection, as we saw in the case of the peppered moth . Take the Self-Test for this lecture. Links Send feedback to the Global Change Webmaster .