Reciprocating dispersal by habitat-selecting white-footed mice

Theories of dispersal driven by density-dependent habitat selection demonstrate that putative examples of source-sink dynamics and balanced dispersal may also be explained by a more general pattern of bi-directional, reciprocating dispersal. Analyses of 19 years of data on dispersal by white-footed mice confirm the theory. Fitness of territorial white-footed mice living in an agricultural mosaic is higher in forest habitat than it is in either edge or fencerows. Density-dependent habitat selection theory predicts that if net emigration by mice flows from the forest to forest-edge during periods of population growth, animals should subsequently move from the edge to forest during population decline. The pattern of mouse dispersal varies between seasons as populations wax and wane in abundance. Mice tend, as predicted, to move from high-density forest habitat into low-density edge during periods of population increase, and from the low-density edge into high-density forest during periods of population decline. Over all years combined, dispersal by white-footed mice was balanced. Each habitat tended to gain as many dispersing individuals as it lost. The results support a conditional dispersal strategy linked to density-dependent habitat selection, but also suggest the possibility of multiple coexisting strategies.