Dispersal, kin competition, and the ideal free distribution in a spatially heterogeneous population

In this paper, we reanalyze simple models of the evolution of dispersal in a heterogeneous landscape. Previous analyses concluded that without temporal variability, dispersal can evolve only if it is not costly and if it is conditional on the habitat. If both conditions hold, these models predict that selection on dispersal should lead to balanced dispersal between habitats (the number of immigrants equals the number of emigrants in each habitat). To evaluate the generality of these conclusions, we extended the analysis of these models to finite populations. This requires us to establish fitness measures for finite class-structured populations. These fitness measures allow us to take kin competition into account. Our analysis shows that even without temporal variability, conditional dispersal and the absence of a dispersal cost are not necessary conditions for dispersal to evolve. In the absence of a dispersal cost, we predict that selection on conditional dispersal will always lead to panmixia and not simply to balanced dispersal. When dispersal is costly, we show that the ideal free distribution (IFD) and balanced dispersal do not occur. Our results show that the deviations from IFD are of the order of the dispersal cost. We propose an approach to test our predictions.