In mammals generally, and in meadow voles in particular, males tend to move greater distances than females between their place of birth and the location of their initial breeding attempt. Considerable controversy exists over the cause or causes of this pattern of movement known as male-biased natal dispersal. One explanation, the inbreeding avoidance hypothesis, states that the sexes move different distances to avoid mating with close relatives because of the potentially deleterious effects of inbreeding. A second possibility, the competition- for-mates hypothesis, suggests that competition among males for mates causes male-biased dispersal. This study proposes to experimentally examine these 2 hypotheses. Laboratory-reared meadow voles will be released into small, uniform patches of grassland habitat, and their dispersal from these patches will be monitored. Sibling groups will be released into some plots and non-sibling groups into other plots. These groups will consist of either 3 males and 1 female or 3 females and 1 male. Greater dispersal from patches containing siblings will support inbreeding avoidance as a cause of dispersal patterns in mammals, whereas dispersal from patches with male-biased sex ratios will suggest competition for mates is important. This proposed study is one of the first to test experimentally these 2 hypotheses. It should provide valuable information concerning why male mammals tend to disperse greater distance than females.
