Effects of patch quality on dispersal and social organization of prairie voles: An experimental approach

The quality of the habitat patch in which individuals reside may influence demographic processes, thus affecting social organization. We manipulated the risk of predation and food availability to test the hypothesis that high patch quality decreased the propensity to disperse, increased the likelihood of social units becoming groups, and increased overall group size in prairie voles (Microtus ochrogaster). Prairie voles are socially monogamous, at least in part of their range, and they display varied social organization within a population, including groups (containing a breeding pair and at least I additional adult of either sex), male-female pairs, and single females. Our results indicated that the likelihood of dispersal from high-quality patches was significantly less than from low-quality patches. Dispersers also were significantly more likely to settle in similar or higher quality patches than the ones in which they were originally released. These patterns were primarily due to the dispersal of young males. Although the proportion of social units that were groups appeared to decrease with lower patch quality, the difference in social organization among patch types was not statistically significant. The total number of founding voles and founding males per social unit residing in the highest quality patches at the end of the study were significantly greater than in the lowest quality patches. Thus, under the conditions of our experiment, patch quality affected dispersal and group size but not the tendency to form groups.