The present status of the competitive exclusion principle.

Since Darwin accepted the Malthusian population theory to solve the demographic problems he thought to be logically connected with the universal operation of natural selection, the numerical processes in both populations and communities were generally supposed to be governed by competition. For interspecific relations this found expression in the 'competitive exclusion principle'. After it was shown that coexistence rather than exclusion of closely related species is the rule, this principle gradually changed into the 'competitive niche shift principle'. Recently the universality of competition has been increasingly questioned, so that other interspecific relationships (especially predation) are revaluated as possibly governing many natural population and inter-population processes.