NATAL DISPERSAL AND SOCIAL-DOMINANCE IN THE COMMON SHREW SOREX-ARANEUS

We trapped shrews during 5 summers on small islets in a lake. All young shrews (n = 55) caught from the islets were natal dispersers. We used several skeletal characters to compare the morphology of the dispersers and the mainland residents. In 3 yr the dispersers were significantly smaller in body size (weight of bones) than the residents, and/or the dispersers had significantly smaller values of specific mandibular characters. These same mandibular characters (but not body weight) were significantly correlated with an individual's performance in neutral arena tests. In the remaining 2 yr, the density of shrews and microtine rodents was high on the mainland, the rate of dispersal to islets was higher than in the other years, and young shrews showed an increased level of fluctuating asymmetry of bilateral morphological characters; but the only morphological differences between the dispersers and the residents were in the lengths of the tibia and hind foot, which were longer in the dispersers. Our results suggest that social subordinates predominated among the dispersers when density and dispersal rate were low (in 3 yr), but when density of shrews and rodents on the mainland was high, dispersal was common and apparently not related to the social position of individuals (in 2 yr).