Two species occupying the same niche cannot exploit the same array of , especially a single , without one or the other being driven .

This tendency of one species to drive similar species to extinction is called competitive exclusion, meaning that through one of the species is excluded from the common environment. Extinction of one of the occurs when one or the other species will be more effective in . Typically it will be the case that one competitor is indeed more effective though this is not always the case.

Note that implicit assumptions with the above ideas are such things as a lack of as well as a lack of a common predator to both competitors since these features can result either in the not being limiting or a reduced ability to compete head to head for the same resources. Nonetheless, competitive exclusion represents a good default assumption when exploring issues of interspecific competition.