A niche-modelling approach to understanding late-Quaternary megafaunal extinctions

A number of large mammals ('megafauna') became extinct towards, or following, the end of the last glacial period. The cause of their extinction, and in particular the reason why some species went extinct, whereas other large mammals survived to the present day in the same regions, remains a matter of debate amongst scientists. Two principal hypotheses have been advanced to account for the extinctions. Firstly, it is suggested that the major climatic changes and associated ecological upheavals of the end of the glacial stage resulted in the conditions to which the species were adapted no longer being available to them. Secondly, given the coincidence of the extinctions with an increasing population and expanding geographical range of humans, it is suggested that human activities, principally the pressures exerted upon the megafaunal populations by hunting, caused the extinctions. We propose to adopt a new approach to investigating these extinctions and to discriminating between these alternative explanations. Our research will uniquely combine: (i) detailed dating information from high quality radiocarbon dates made directly on fossils of megafaunal species (ii) simulations of past climate for the periods of interest made using the same kind of climate model as is used to simulate potential future climates; and (iii) evidence of megafaunal species' habitats and diets. The latter will be inferred from: (i) simulations of past vegetation; (ii) records of past vegetation; and (iii) those rare instances where fossils of megafaunal species are found directly associated with plant remains, notably in the case of fossils from the permafrost in which the stomach contents are preserved. We will use these data to construct models relating the megafaunal species' geographical ranges to climate, habitat and components of their diet. We will then use these models to simulate the changing potential range of each species. The models and these simulations will enable us to assess the series of hypotheses, testing of which is the principal aim of our study. Our study will encompass all of northern Eurasia and North America, enabling us to include the complete geographical ranges of species that ranged across both continents in the past, and will extend from about 50,000 years ago to about 5,000 years ago. In addition to studying a range of extinct species, including herbivores, carnivores and omnivores, we will also examine a comparable range of species that survive to the present day. In these cases we will also use data recording the species' current geographical distributions. By examining both extinct and surviving species we will be able to make critical comparisons that will provide insight into the factors determining which species survived and which suffered extinction. The results of our study will help elucidate the relative importance of environmental, especially climatic, change, of the ecological characteristics of the species themselves, and of human activities, in causing the extinctions.