THE TROPHIC POSITION OF PLEISTOCENE AND MODERN BROWN BEARS (URSUS ARCTOS) OF YAKUTIA, BASED ON STABLE ISOTOPE ANALYSES

摘要

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 delta C-13 values typical of terrestrial ecosystems and relatively high delta N-15 values typical of such Pleistocene predators as the cave lion. We explain the high delta N-15 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, this allowing for large amounts of animal food to be used by the bears; (2) the physiological effect of hibernation, expressed in the increased content of N-15 in bone collagen; (3) due to more severe climatic conditions, an increased content of N-15 in vegetation, this affecting the isotopic composition of the entire mammoth fauna of western Beringia. The delta C-13 and delta N-15 values of modern brown bears in Yakutia indicate a plant diet, this showing that modern brown bears (compared to fossils) occupy a fundamentally different trophic niche adapted to modern low-productivity ecosystems of Yakutia.