Variation in space and time: a long-term examination of density-dependent dispersal in a woodland rodent

Dispersal is a fundamental ecological process, and population density has been observed as a driver of dispersal in various taxa. Conflicting examples of positive and negative density-dependent dispersal, however, leave little consensus regarding any general effects of density on dispersal. Deer mice (Peromyscus maniculatus) have exhibited both negative and positive density-dependent dispersal. Using 51-years of data on P. maniculatus live-trapping abundances, we examined the spatial scale of density-dependent dispersal as well as its temporal stability within this long time-series. We examined these patterns over both the entire time-series and also in ten-year shifting windows to determine whether the nature and strength of the relationship changed through time. Overall, the probability of dispersal decreased with increased local and regional population density, and the negative effect of local density on dispersal was more pronounced in years with low regional densities. Females were less likely to disperse, but female dispersal was more density-dependent than male dispersal. Additionally, the strength of negative density-dependent dispersal changed through time, from very strong in some decades to absent in others. Our study shows that the relationship between density and dispersal is not temporally static and that studies of density-dependent dispersal should consider both local and regional population densities. As well, while male-biased dispersal is often considered ubiquitous in mammals, we demonstrate that male and female dispersal may have differing levels of density-dependence. Finally, our study highlights the importance of accounting for both local and regional processes in natural systems as these types of long-term, spatially broad examinations of dispersal are crucial if spatial processes are to be represented adequately and accurately in population modelling and theory.