Local Resource Heterogeneity Drives Density-Dependent Dispersal Expression in a Phoretic Mite

Dispersal is favoured in heterogenous and ephemeral environments, where it allows individuals to move and access alternate patches. However, whilst heterogeneity across habitats favours dispersal evolutionarily, little is known about how resource heterogeneity at the source habitat-local heterogeneity-may cue dispersal expression. Local heterogeneity is likely important, as it may drive local competition and encourage movement around the local environment. We assessed the role of local resource heterogeneity on the expression of a plastic dispersal phenotype in experimental populations of the bulb mite Rhizoglyphus robini through a multigenerational experiment. Populations were kept under either heterogenous, homogenous or intermediate food distribution treatments, and at low or high population density, via culling. Thus, we tested for the effect of local resource heterogeneity and competition on dispersal expression. Additionally, we used our findings to understand the influence of compensatory growth, induced by culling, on population demography. We found that heterogenous environments induce greater dispersal expression in high-density environments, but not in low-density ones. Culled treatments had on average larger population sizes than other treatments, but no significant differences were found in growth rates. Relative abundance of both eggs and juveniles in comparison to adults was also significantly determined by experimental treatment, particularly culling. We infer that heterogeneity exacerbates perceived local level competition. We also propose that culled populations grow at a higher rate than non-culled, at least in the short-term, due to compensatory reproduction. Overall, we find a significant impact of local heterogeneity on population size and dispersal expression, much of which may arise due to the influences of heterogeneity on competition around foraging spaces. Findings highlight the pervasive effects of heterogeneity across ecological scales, and the need to distinguish between local and regional processes when modelling dispersal.