Sustainable harvest or resource depression? Using ancient DNA to study the population dynamics of guanaco in western Argentina during the Holocene

Zooarchaeologists have relied upon various approaches to study the impacts of harvest pressure and environmental change on ungulate populations, such as analysis of prey mortality patterns and morphometrics. Analysis of ancient DNA from ungulate bones and bone fragments from archaeological sites provides an additional means for studying prey population dynamics related to environmental change and human ecology over time. In this paper, we study the population history of the largest game animal in northwest Patagonia, the guanaco (Lama guanicoe). Our study relies on the use of Bayesian Skyline Plots to determine shifts in estimated guanaco population size based on analysis of ancient mitochondrial DNA. Our results indicate that hunting by humans in addition to increases in aridity during the late Holocene led to a decline in the guanaco population in the region, which is in contrast to the harvest and environmental history in other parts of Patagonia (south of our study area). Using a weight of evidence approach that includes proxies of environmental change, human population dynamics, exploitation of guanacos, and estimates of guanaco population size, we argue that the late Holocene shift in guanaco population size was a driving factor in subsistence and settlement change related to resource intensification during the late Holocene in northwest Patagonia.