Investigating ancient bison migration in Alaska: a bottom up approach using isotopes

Abstract

Once abundant in the Arctic, bison (Bison bison) declined almost to extinction in the North but have subsequently been reintroduced into Alaska. The predecessors of these modern bison were the ancient steppe bison (Bison priscus), which were abundant throughout the Northern Hemisphere before their extinction during the Holocene. This thesis investigates the ecology and landscape-use of both the present-day wood bison (Bison bison athabascae) and the ancient steppe bison in Alaska using stable isotopes, among other methods. The stable carbon and nitrogen isotope compositions of animal tissues are traditionally used to investigate diet. However, this thesis uses the isotope composition of tail hairs from present day wood bison as a proxy for their nutritional stress. Nutritional stress of some wood bison appears to be influenced not only by food shortage during hard seasons, but also due to long-distance mobility. This insight provides a key to understanding the challenges of reintroduction of the species into Alaska today, and can also be applied to understand the nutritional stress and cost of dispersal by ancient animals. Whereas the mobility of present-day bison can be tracked using sophisticated satellite tracking technologies, studies of the paleo-mobility of ancient bison rely on isotopic markers such as strontium and oxygen isotope ratios preserved in their teeth. To aid this approach using isotopic geolocation, this thesis creates a map of bioavailable strontium modeled and based on strontium isotope composition of present-day rodent teeth from across Alaska. It then compares this map, together with an existing oxygen isotope map of precipitation in Alaska, with the strontium and oxygen isotopes preserved in a suite of ancient bison from Northern Alaska. This comparison brings to light some of the major habitation regions used by Bison on the North Slope of Alaska over the last ~50,000 years. Finally, these findings subsequently contribute to a detailed paleoecological investigation of a mostly articulated and complete ancient steppe bison found on the North Slope of Alaska. This final study reveals the life-history of an individual bison that dispersed from the coastal plain to the foothills of the Brooks Range early in his life, and shows that the trip was nutritionally costly. This information is combined with a suite of other paleoecological methods to provide a vivid life history of this ancient bison. We introduce new methodologies for studying these ancient animals that seek to bridge the gap between how we study present-day and the past.