MOVEMENT OF VOLES ACROSS HABITAT BOUNDARIES: EFFECTS OF FOOD AND COVER

We tested hypotheses about factors likely to influence movements of prairie voles (Microtus ochrogaster) and meadow voles (M. pennsylvanicus) between habitat patches that differed in availability of high-quality food and amount of vegetative cover. More emigration (per capita) occurred from low-quality habitats than from high-quality habitats. A greater proportion of emigrants from high-quality habitats returned to home habitats than did those from low-quality habitats. More emigrant prairie voles moved toward habitats with supplemental food, and more emigrants moved toward the nearest receiving habitat. Prairie voles (a monogamous species) showed greater than expected permanent emigration by subadults, whereas meadow voles (a promiscuous species) showed greater than expected permanent emigration by males. These patterns largely support predictions from evolutionary theories of dispersal. Emigrating female voles, but not males, selectively settled in habitats with supplemental food, which supports the hypothesis that females respond to resource availability but males respond to availability of females. Overall, movement patterns reported here and density-dependent declines in fitness reported previously indicate that movements across habitat boundaries tend to equalize fitness of residents in habitats of different quality, consistent with the hypothesis that voles have an ideal-free distribution across habitats.