Ecological Character Displacement in a Variable Environment

We analyzed a simple genetic model of ecological character displacement in a fluctuating environment. Character states of two identical, competing species were determined by a single-gene, two-allele model. In each generation, the carrying capacity of different segments of a uniform resource spectrum fluctuated randomly. Interand intraspecific exploitation competition reduced litnesses of similar genotypes. In contrast to demographic models of niche shift, this genetic model led to a high average overlap of species in a variable environment. However, for moderate or small environmental fluctuations, character distributions of the two species diverged signilicantly and rapidly. Results were nearly identical for a model of environmental fluctuations that incorporated resource “crunches.” These models were sensitive to the intrinsic rate of increase of the competing species: divergence was substantially slower at small values of r. Nevertheless, most simulations of this simple genetic model suggest that interspecific competition can lead to significant divergence, even in a moderately fluctuating environment.