competition, in biology, relationship between members of the same or different species in which individuals are adversely affected by those having the same living requirements, such as food or space. Intraspecific competition, i.e., competition among members of the same species, is illustrated by some species of birds and mammals, the males of which set up territories from which all other males of the same species are excluded. In interspecific competition members of different species compete for the same ecologically limiting factors, such as a food source. Not all relationships among organisms are competitive; for example, the commensal relationship between members of different species is noncompetitive (see commensalism).
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