Intergall migration in aphids; a model and a test of ESS dispersal rate

Summary I present an inclusive-fitness model for the evolution of dispersal rates of the offspring of asexual organisms living in discrete sites, which vary in available resources. I also assume a stable and saturated condition and that the offspring can respond to the variation in the capacity (amount of resources) of their natal sites. The model was tested using data obtained from the intergall migration in the yezo-spruce gall aphid,Adelges japonicus. All the parameters needed for the model, which included the cost of dispersal, both dispersal rates and available resources in each site, were estimated from field examinations. The data fit the model well, suggesting the importance of kin selection in determining the dispersal rates. Both actual and ESS dispersal rates are shown as concave functions of site capacity with a minimum rate for intermediate site capacity. The effect of both actual and ESS dispersal is to reduce, but not eliminate sibling competition within natal sites, which is most severe in intermediate site capacity.