JUVENILE DISPERSAL IN RELATION TO ADULT DENSITIES IN WOOD MICE APODEMUS-SYLVATICUS

Two alternative hypotheses explaining low densities of juvenile wood m ice Apodemus sylvaticus (Linnaeus, 1758) early in the breeding season were compared: the Adult Aggression Hypothesis and the Habitat Saturat ion Hypothesis. They predict different ratios between adult and juveni le densities, which were tested using trapping data from mixed deciduo us woodland and from lowland arable field margins. According to the Ad ult Aggression Hypothesis, juveniles have a poor persistence rate earl y in the breeding season as a result of aggressive behaviour shown by the adults. As the breeding season progresses, a drop in adult aggress ion levels results in increased juvenile persistence, which, in turn, leads to increased densities. The Habitat Saturation Hypothesis propos es that juveniles disperse from their parents' territories until the s urrounding habitats are saturated and that this gradual saturation res ults in increased densities as the breeding season progresses. The obs erved correlations between adult and juvenile densities both in woodla nd and on field margins were consistent with the predictions of the Ha bitat Saturation Hypothesis.