An Explicit Genetic Model for Ecological Character Displacement

Abstract

Realistic models for ecological character displacement should incorporate population genetics. In Slatkin's pioneering model (Slatkin 1980), the genetics of the quantitative character determining the competitive interactions are modeled by assuming that the character is normally distributed in each generation. Only the mean and the variance of the character distributions change over time. With symmetric ecological assumptions for the two competing species, and with normally distributed resources that are equally used by both species, this model did not yield significant displacement. This has led to the belief that ecological asymmetries or constraints on resource use, e.g., by constraining the phenotypic variances, are necessary for character displacement. I argue that the reason for the negative result in Slatkin's original model is that the genetics are modeled too rigidly. With a more flexible genetic model, obtained by explicitly modeling many loci with additive effects, character displacement occurs as a rule even for symmetric ecological assumptions and without constraints on the phenotype distributions. The model can also be used in other contexts than competition for resources. For example, character displacement in a host—parasite system can lead to parasite specialization. The results suggest that more detailed genetic models yield a finer resolution of the interaction between population genetics and ecological dynamics. Explicit genetics lead to more insights than the usual quantitative genetic assumption of normal character distribution.