Predation

Predation is the act of one animal hunting, killing, and eating another animal. A predator is an animal that survives by killing and eating other animals. Predation can be important in regulating the size of a prey species (the hunted animal). It is also a mechanism of evolution since it weeds out animals that are poorly adapted to being hunted, or to their environment, thus promoting adaptation by natural selection.

Predation can be coldly described as nature's "kill or be killed" approach to who survives in the wild and who does not. While there are some species of animals that have no natural enemies or are simply too difficult to catch and eat (such as a mature, healthy elephant), virtually all animals are at some point in their lives either predator or prey. All predators are heterotrophs, meaning that they cannot make their own food as plants (autotrophs) do, so they must consume another organism and digest it to obtain its energy. Many animals are herbivores (planteaters) and do not kill other animals to eat. They eat living plants that do not have to be hunted, caught, and killed before they can be consumed. Animals that exclusively eat plants are not considered predators

(although from a living plant's point of view, it could be said that the plant is being preyed upon). Carnivorous animals as well as omnivores are predators, since carnivores exclusively eat other animals, and omnivores eat both plants and animals, usually according to what is available.

Successful predation requires that a catch be made, and a catch can occur in a great variety of ways. Spiders spin webs to trap their prey; cats lie in wait for the proper moment to spring; hyenas stalk in groups and exhaust their prey; and humans use their technology to kill from a distance. Specialized predators usually go after a single species, while generalized predators will feed on a variety of other species. Predation is one of the ways in which nature selects who has done the best job of adapting to its environment and who will have the best chance to survive. In this way, predation can be said to be a mechanism or a means that nature employs to continue the important role of evolution.

Predators almost always select a meal that will give them more energy than they will use up to catch it. When faced with an opportunity to select an individual animal from a group to eat, predators will usually select the easiest to catch, such as the weakest, the slowest, or the youngest or oldest. Those animals that are poorly adapted will probably not survive and therefore not be able to pass on their poorly adapted traits to another generation. In the dynamic relationship between predator and prey, there is a continuing type of improvement that goes on in which the prey that survive pass on traits that make their offspring slightly better at avoiding being caught. On the other hand, predators that survive because they are excellent hunters will also pass on the good traits that made them better at catching prey. So in the long run, the seemingly cruel standards of the natural world use predation to improve the species.

In terms of entire populations in a certain habitat, predator and prey relationships often move along the same lines. Thus, when conditions favor a prey population—such as when field mice thrive during a good growing season and their population increases—the predator population will also be well fed and grow larger as its members grow strong and live longer. The opposite happens when populations drop. Finally, when the only predator of a certain species disappears (sometimes human intervention causes this to happen), prey populations will take off. The systematic killing of timber wolves and gray wolves in the American West has led to an increase in the number of rabbits and rodents that regularly served as their prey.

[See alsoEvolution; Natural Selection; Survival of the Fittest ]