Pleistocene megafauna from eastern Beringia: Paleoecological and paleoenvironmental interpretations of stable carbon and nitrogen isotope and radiocarbon records

Abstract

Late Pleistocene eastern Beringia is a model paleo-ecosystem for the study of potential and realized species interactions within a diverse mammalian fauna. Beringian paleontological records store a wealth of information that can be used to investigate how predator–prey and competitive interactions among consumers shifted in response to past episodes of environmental change. Two such recent periods of rapid climate change are the Last Glacial Maximum (LGM) and the end of glacial conditions at the beginning of the Holocene. Here we assemble carbon and nitrogen stable isotope, and AMS 14C data collected from bone collagen of late Pleistocene carnivores and megafaunal prey species from the interior of eastern Beringia (Alaska), and reconstruct the diets of ancient Alaskan carnivores and herbivores. We are able to account for the relative influences of diet versus changing environmental conditions on variances in consumer isotope values, to identify species hiatuses in the fossil record, and to draw conclusions about paleoenvironmental conditions from faunal chronologies. Our isotopic results suggest that there was dietary niche overlap among some Beringian herbivore species, and partitioning among other species. We rely upon δ 13C and δ 15N values of modern Alaskan C 3 plant types to infer Beringian herbivore dietary niches. Horse, bison, yak, and mammoth primarily consumed grasses, sedges, and herbaceous plant species. Caribou and woodland muskox focused upon tundra plants, including lichen, fungi, and mosses. The network of Beringian carnivore interaction was complex and dynamic; some species (wolves) persisted for long periods of time, while others were only present during specific timeframes (large felids and ursids). Beringian carnivore diets included all measured herbivore species, although mammoth and muskox only appeared in carnivore diets during specific times in the late Pleistocene. We identified the potential presence of unmeasured diet sources that may have included forest-dwelling cervids and/or plant materials. None of the large-bodied carnivore species we analyzed (except short-faced bear) were specialized predators of a single prey species during the late Pleistocene. Differences in carnivore diet and dietary breadth between time periods either reflect changes in the relative abundances of prey on the Beringian landscape, or changes in competitive interactions among Beringian carnivore species.