Heavy reliance on plants for Romanian cave bears evidenced by amino acid nitrogen isotope analysis

Heavy reliance on plants is rare in Carnivora and mostly limited to relatively small species in subtropical settings. The feeding behaviors of extinct cave bears living during Pleistocene cold periods at middle latitudes have been intensely studied using various approaches including isotopic analyses of fossil collagen. In contrast to cave bears from all other regions in Europe, some individuals from Romania show exceptionally high δ(15)N values that might be indicative of meat consumption. Herbivory on plants with high δ(15)N values cannot be ruled out based on this method, however. Here we apply an approach using the δ(15)N values of individual amino acids from collagen that offsets the baseline δ(15)N variation among environments. The analysis yielded strong signals of reliance on plants for Romanian cave bears based on the δ(15)N values of glutamate and phenylalanine. These results could suggest that the high variability in bulk collagen δ(15)N values observed among cave bears in Romania reflects niche partitioning but in a general trophic context of herbivory.