Habitat selection of the Eurasian beaver (Castor fiber) near its carrying capacity: an example from Norway

The Eurasian beaver (Castor fiber L., 1758) was extirpated until the beginning of the twentieth century, but is becoming re-established over much of its former range. Since this rodent is considered both a keystone species and an ecosystem engineer, it is important to understand its habitat use in a population near its carrying capacity. In this study, we tested the hypothesis that habitat selection in beaver populations near their carrying capacities is different from populations that are still expanding. Also, a resource-selection model for the species using logistic regression was derived. Although most of the tested habitat variables were important for both populations expanding and populations near their carrying capacities, there were significant differences in the importance of the presence of shrub and (or) hardwood on the riverbank and the river flow speed. Beaver presence was associated with narrower river widths, bank slope, water depth close to the bank, silt-soil bank substrates, cover of deciduous forest, and cover of shrub and (or) hardwood on the bank. The models had high overall accuracy (overall correct classification > 85%, area under the curve > 90%). The final model is thought to be robust and applicable to areas with similar river and vegetation characteristics. Our results extend the habitat selection patterns of beavers to patterns at high-density populations.