Competition and Coexistence of Similar Species

Abstract

a basic question in ecology is Hutchinson’s (1959) classic, Why are there so many animals (or plants!)? The way in which this question is answered depends to some extent on the scientific background of the researcher. The systematist or geneticist might attack the problem from the viewpoints of sympatric speciation, variations in breeding systems, ecotypic variation, phenotypic plasticity, patterns of gene flow, phenology, etc. Almost all of these approaches attempt to explain how species or ecotypes do or do not remain isolated from each other (often with hypotheses relating to the evolutionary development of the phenomena), but not how they manage to coexist in the same habitat. To a geneticist, the problem of species range, abundances, and cooccurrence may be mainly a genetics problem; i.e., each species is viewed as limited by its genetic “equipment” (see Antonovics, 1976b). What quality of the environment selects for various genetic schemes may be of interest only secondarily. An ecologist may approach the problem by finding some phenotypic character, morphological or physiological, that differs systematically among a group of similar plants and then ascribe to those differences a mechanism(s) that allows coexistence. This approach seems more promising in relating environmental factors to organism constraints, but, without additional experimental manipulation or genetics study, it cannot be demonstrated that the proposed mechanism is in fact operating to produce the species distributions observed in the field.