Spatial models that couple demography and dispersal are important tools for understanding and predicting range expansion by invasive organisms. In current models, dispersal is characterized by a stationary distribution of individual movement distances. However, for many organisms, dispersal distance is influenced by local population density. Furthermore, in dioecious species (i.e., most animals), females and males may differ in the sensitivity of their dispersal behavior to local density; such sex-specific responses would skew the sex ratio at an invasion’s leading edge. We developed models to explore the dynamical consequences of density-dependent dispersal in the spatial spread dynamics of a two-sex biological invasion. We integrated our theoretical models with dispersal studies of the bean beetle Callosobruchus maculatus in the laboratory.
Results/Conclusions
Our theoretical results show that sex-specific, density-dependent dispersal can accelerate range expansion but the degree to which it does so depends upon complex interactions between sex-specific movement and local, two-sex population growth dynamics. Our experiments showed that C. maculatus exhibits sex-specific, density-dependent dispersal behavior (males but not females disperse greater distances in response to local density). Experimental beetle invasions, in which we manipulated the dispersal response to density, provide support for the quantitative predictions of our theoretical model. Our integrative theoretical/experimental approach demonstrates how accounting for the biological details of dispersal, including density dependence and sex differences, can enhance prediction of range expansion dynamics.