Habitat heterogeneities versus spatial type frequency variances as driving forces of dispersal evolution

Abstract

Understanding the evolution of dispersal is essential for understanding and predicting the dynamics of natural populations. Two main factors are known to influence dispersal evolution: spatio-temporal variation in the environment and relatedness between individuals. However, the relation between these factors is still poorly understood, and they are usually treated separately. In this article, I present a theoretical framework that contains and connects effects of both environmental variation and relatedness, and reproduces and extends their known features. Spatial habitat variation selects for balanced dispersal strategies, whereby the population is kept at an ideal free distribution. Within this class of dispersal strategies, I explain how increased dispersal is promoted by perturbations to the dispersal type frequencies. An explicit formula shows the magnitude of the selective advantage of increased dispersal in terms of the spatial variability in the frequencies of the different dispersal strategies present. These variances are capable of capturing various sources of stochasticity and hence establish a common scale for their effects on the evolution of dispersal. The results furthermore indicate an alternative approach to identifying effects of relatedness on dispersal evolution. This article presents a theoretical framework that brings together spatial habitat heterogeneities and kin selection models for the evolution of dispersal in a conceptually illuminative way. The impact of the former is measured in terms of spatial fluxes of individuals, while the effect of relatedness is expressed via type frequency variances, which provides striking insight: any force that induces variation into the dispersal type frequencies causes selection for increased dispersal. Consequently, a common scale for different factors of dispersal evolution is established, indicating that future studies should focus on the type frequency variability as a force promoting dispersal.