SURVIVAL OF THE FLEXIBLE? A COMPARISON OF DIETARY STRATEGIES BETWEEN LATE PLEISTOCENE BERINGIAN BISON AND HORSES

Bison and horses were the most abundant species of the “Mammoth Steppe”, coexisting with a diverse assemblage of other large mammals including wooly mammoths, musk oxen, saiga antelope, and caribou during the late Pleistocene in Beringia. However, while the Steppe Bison (Bison priscus) survived at least into the mid Holocene and modern wood bison (Bison bison athabascae) continue to live in Alaska and northwestern Canada today, horses and many other large mammals of Beringia went extinct at the end of the Pleistocene, concurrent with the collapse of the Mammoth Steppe ecosystem. Though modern horses and bison are both considered obligate grazers, isotopic and dental evidence suggest that Pleistocene bison sometimes utilized a more “mixed feeding” dietary strategy, incorporating more shrubs and woody browse in their diets. Broader dietary preferences could confer a survival advantage during the environmental shifts of the Pleistocene-Holocene transition. Dietary reconstructions of Beringian herbivores based on stable isotope data have indicated potential dietary discrimination between bison and horses, though the dominance of C₃ plants in northern climates complicates dietary interpretations based solely on stable isotope data. To test whether Beringian bison had greater dietary flexibility than horses, we assessed dietary niche using Dental Microwear Texture Analysis (DMTA). We find that both bison and horses have dental microwear textures indicative of primarily grazing diets. Further, DMTA suggests that diets were similar between populations along the North Slope of Alaska and interior Beringia (Yukon, Canada). For bison, variation in dental microwear textures decreased significantly going into the Last Glacial Maximum and continued to be reduced through the Pleistocene-Holocene transition. These results suggest that differences in dietary niche may not explain the survival of bison and the extinction of horses. However, at least bison populations experienced reduced dietary variability concordant with shifts in late Pleistocene vegetation regimes, a potential indication of dietary stress. Dietary stress may have been a confounding factor contributing to end-Pleistocene extinctions and population reductions in Beringia.