Variable Density-Dependent Dispersal and its Metapopulation-Level Consequences

Abstract

Dispersal has far-reaching implications not only for the fitness of individuals but also the structure and viability of populations. This makes it crucial to develop an understanding of both the factors that drive dispersal as well as how variation in dispersal can alter the spatial structure of populations. While it is well documented that population densities can affect rates of dispersal in many taxa, numerous questions remain regarding how variation in the density-dependence of dispersal can arise, and what the consequences of said variation might be at a metapopulation level. In my thesis I use 51-years of small mammal live-trapping data to examine how density affects dispersal at broad spatial and temporal scales, while considering the effects of both conspecifics and heterospecifics, as well as the possible downstream effects on metapopulation structure that may result from variation in the strength of density-dependent dispersal. In my second chapter, I examined density-dependent dispersal in deer mice (Peromyscus maniculatus), demonstrating that this species is more likely to disperse from areas of low local densities (negative-density dependent dispersal) and that this effect is more pronounced in years where regional densities are also low. I also show that the strength of density-dependent dispersal in this species is not temporally static. In my third chapter, I investigated interspecific density- dependent dispersal among multiple small mammal species. I show that there may be heterospecific effects on dispersal for some species in the community. In my fourth chapter, I looked at whether variation in the strength of density dependent dispersal resulted in predictable changes in metapopulation structure in multiple small mammal metapopulations. I find that metapopulation heterogeneity may potentially increase due to variation in density-dependent dispersal for some species. Overall, my thesis contributes to a more nuanced picture of density- dependent dispersal by expanding our current understanding of the context-dependence of density-dependent dispersal, the potential for intratrophic interspecific density effects on dispersal, and the potential for variable density-dependent dispersal to lead to variation in the spatial structure of populations.