Feeding habits may explain the morphological uniqueness of brown bears on Etorofu Island, Southern Kuril Islands in East Asia

Abstract

The brown bear (Ursus arctos) population on Etorofu Island, Southern Kuril Islands, has several unique morphological features: (1) the presence of white-pelage bears within the population and (2) a larger body size than bears on a larger neighbour island, Hokkaido Island. Nevertheless, little ecological information is available about Etorofu brown bears. In the present study, we reveal the unique feeding habits of Etorofu brown bears and suggest that their unique morphological features and diet are related. The feeding habits of brown bears on Etorofu Island were assessed using carbon, nitrogen, and sulfur stable isotope analysis, and their feeding habits were compared with those of bears on the eastern side of Hokkaido Island. According to the stable isotope analysis, the dependence on salmon is great for bears on Etorofu but only slight for bears on Hokkaido. Our results suggest that the feeding habits of Etorofu brown bears may explain their unique morphological features because a white pelage colour confers an advantage when catching salmon, and a carnivorous diet can make their body size larger. The variation in feeding habits can be an important driver of the speciation and evolution of animals.