The Trophic Position of Pleistocene and Modern Brown Bears (Ursus arctos) of Yakutia Based on Stable Isotope Analyses

Abstract

To assess the trophic position of the exceptionally large-sized brown bears from the Pleistocene of Yakutia, we used stable nitrogen and carbon isotope analyses of the collagen contained in fossil bones and teeth. Modern brown bears of Yakutia were compared to the large Pleistocene predators. As a result of the measurements taken for the Pleistocene bears, we obtained δ13С values typical of terrestrial ecosystems and relatively high δ15N values typical of such Pleistocene predators as the cave lion. We explain the high δ15N values of the bone collagen of the study fossil bears, as well as other Pleistocene brown bears of Yakutia and Chukotka, by (1) the absence of large competitors such as Arctodus simus, which allowed the bears to use large amounts of animal food; (2) the physiological effect of hibernation, expressed in an increased content of 15N in the bone collagen; and (3) an increased content of 15N in vegetation due to more severe climatic conditions, which affects the isotopic composition of the entire mammoth fauna of western Beringia. The δ13C and δ15N values of modern brown bears in Yakutia indicate a plant diet, suggesting that the modern brown bears (compared to fossils) occupy a fundamentally different trophic niche adapted to the modern low-productivity ecosystems of Yakutia.