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“Page 308 The Competitive Exclusion Principle. No two organisms that compete in every activity can coexist indefinitely in the same environment. To coexist in time, organisms that are potentially completely competitive must be geographically isolated from each other. Otherwise, the one that is the less efficient yields to the more efficient, no matter how slight the difference. When two competing organisms coexist in the same geographical region, close examination always shows that they are not complete competitors, that one of them draws on a resource of the environment that is not available to the other. The corollary of the principle is that where there is no geographical isolation of genetically and reproductively isolated populations, there must be as many ecological niches as there are populations. The necessary condition for geographical coexistence is ecological specialization.” — Garrett Hardin