Competition is an interaction between two organisms in which both could potentially be harmed. Competition can occur within or amongst species, and generally occurs when natural resources are limited. Interspecific competition generally results in lower survival and reproduction rates, and lower population sizes of both species. Environmental factors other than the resource being competed for may affect the outcome of competition, giving one or the other species the edge in the competitive battle.
The competitive exclusion principle is a direct result of competition. It is the concept that no two species that have similar patterns of consuming resources can coexist for a prolonged period in an area. One will out-compete the other for the same resources. An important point here is that the two species have the same exact resource use patterns; in that case, one species or the other cannot survive.