Evaluation of tree and shrub resources of the Eurasian beaver (Castor fiber L.) and changes in beaver foraging strategy after resources depletion

Abstract

The results of comparative analysis of tree and shrub resources quantitative characteristics in the active and abandoned beaver habitats within the territory of the Tadenka River basin, Prioksko-Terrasny Nature Reserve, where beavers have been dwelling for more than 60 years, are presented. Using one-way ANOVA analysis with the settlement type (active or abandoned) as a factor, it was shown that long-term foraging by beaver leads to a decrease in the species richness of trees (P = 0.068). Different hypotheses of the impact produced by beaver selective foraging on various forest layers (overstorey and undestorey) are discussed. Factors promoting thinning and changes in the age structure of the overstorey and undestorey are considered. There were observed changes in the species composition, accompanied by an increase in the proportion of low preference and nonfood species. The conclusion is made that, if the foraging zone does not exceed 50 m at the beginning of habitat utilization, it extends up to 165 m in the absence of predators when the habitat is used repeatedly. This observation is confirmed by Fisher’s exact test (P = 0.005), Yates’ chisquared test (P = 0.002), and the likelihood ratio test (P = 0.0002). In the case of beavers recolonizing their abandoned habitats with unrecovered food resources in the Tadenka River basin, a distant zone within 50 to 165 m from the bank becomes the main zone for tree-shrub foraging.