Evolutionary divergence and character displacement in two phenotypically-variable, competing species.

Abstract

Evolutionary divergence depends primarily on incomplete utilization of available resources. Models which incorporate constraints preventing complete utilization of resources, even in the absence of competitors, all predict character displacement. Models which allow greater flexibility of resource use within a species predict correspondingly less divergence. The author extends a model used by Slatkin (1980, 1983) and Taper & Case (1985) which allows each species to fully utilize its resources in the absence of competitors, concentrating on the case in which the species, though similar, differ in their ecological characteristics. The presence of a variety of biological differences between species - including as a subset those which result from resource underutilization - leads to divergence with respect to a quantitatively inherited character, due to interspecific competitive interactions. The resulting displacement can be large and depends little on the parameters chosen. The only exception, involving a character with very low heritability, occurs when the non-interactive phenotypic differences are much greater than those associated with studies of character displacement in natural populations. Thus, under conditions comparable to those encountered in the field, involving similar yet not identical species, evolutionary divergence is a consequence of interspecific competition. -from Author