Paleoecology of Southeastern Saskatchewan bison : changes in diet and environment as inferred through stable isotope analysis of bone collagen

Abstract

Archaeological research has provided evidence of change in the settlement and subsistence practices of human groups inhabiting the Great Plains throughout the Holocene. A substantial part of this reorganization appears to be tied to concurrent changes affecting local bison populations, a species upon which these groups were uniquely dependant. Although bison are thought to have been strongly affected by the severe climates of the Mid-Holocene, there is an absence of appropriate models from which to interpret data in the archaeological and paleontological records. Nevertheless, new techniques are allowing for the determination of ecological information directly from prehistoric remains. This study uses stable isotope ratios (813C, 8'SN, 8D) in bone collagen to examine the dietary ecology of bison in Southern Saskatchewan during eight distinct time periods spanning the last 9,000 years. Stable isotopes of hydrogen and nitrogen in the tissues of animals relate to aspects of local climate, while stable-carbon isotope values reflect dietary choices. When employed in a comparative fashion, these sources may be used to construct simple models of foraging behaviour. The environmental data developed from this investigation appear to correlate generally with patterns predicted by conventional models of Holocene climate. Nevertheless, at least one period of unexpectedly moderate temperature was identified from a context dating to the and Mid-Holocene. The ecological impact of such an episode may have been significant. In addition, the results of this study suggest that bison diet has a complex relationship with local climate. Changes in plant distribution resulting from variations of temperature and precipitation appear to have less of an impact upon bison consumption patterns than do climatically induced changes in the nutritional quality of vegetation. Nevertheless, during specific time periods characterized by similar climatic regimes, their relative consumption of certain forage species (C3 and C4 plants) does not appear to have been consistent. Such a discrepancy may reflect adaptive differences between bison from distinct time periods, or alternatively, the effects of a climatic difference undetectable by isotopic means. In either case, it would appear that bison of the past may have been subject to significant nutritional stresses that could have caused them to behave in fundamentally different ways from modern populations.