Competition
Competition is the interaction between two organisms when both are trying to gain access to the same limited resource. When both organisms are members of the same species, such interaction is said to be "intraspecific competition." When the organisms are from different species, the interaction is "interspecific competition."
Intraspecific competition arises because two members of the same species have nearly identical needs for food, water, sunlight, nesting space, and other aspects of the environment. As long as these resources are available in abundance, every member of the community can survive without competition. When those resources are in limited supply, however, competition is inevitable. For example, a single nesting pair of bald eagles requires a minimum of 620 acres (250 ha) that they can claim as their own territory. If two pairs of eagles try to survive on 620 acres, competition will develop, and the stronger or more aggressive pair will drive out the other pair.
Intraspecific competition is also a factor in controlling plant growth. When a mature plant drops seeds, the seedlings that develop are in competition with the parent plant for water, sunlight, and other resources. When abundant space is available and the size of the community is small, a relatively large number of seedlings can survive and grow. When population density increases, competition becomes more severe and more seedlings die off.
Competition becomes an important limiting factor, therefore, as the size of a community grows. Those individuals in the community that are better adapted to gain food, water, nesting space, or some other limited resource are more likely to survive and reproduce. Intraspecific competition is thus an important factor in natural selection.
Interspecific competition occurs when members of two different species compete for the same limited resource(s). For example, two species of birds might both prefer the same type of insect as a food source and will be forced to compete for it if it is in limited supply.
Laboratory studies show that interspecific competition can result in the extinction of the species less well adapted for a particular resource. However, this result is seldom, if ever, observed in nature,at least among animals. The reason is that individuals can adapt to take advantage of slight differences in resource supplies. In the Galapagos Islands, for example, 13 similar species of finches have evolved from a single parent species. Each species has adapted to take advantage of some particular niche in the environment. As similar as they are, the finches do not compete with each other to any specific extent.
Interspecific competition among plants is a different matter. Since plants are unable to move on their own, they are less able to take advantage of subtle differences in an environment. Situations in which one species of plant takes over an area, causing the extinction of competitors, are well known.
One mechanism that plants use in this battle with each other is the release of toxic chemicals, known as allelochemicals. These chemicals suppress the growth of plants in other—and, sometimes, the same—species. Naturally occurring antibiotics are examples of such allelochemicals.
Resources
Books
Moran, J. M., M. D. Morgan, and J. H. Wiersma. Environmental Science. Dubuque, IA: William C. Brown, 1993.
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