As I have stated in previous blogs, the role of climate and Homo Sapiens in driving the dramatic extinctions of large-bodied mammals during the late Pleistocene period remain contentious (Lorenzen et al 2011). In this blog, I will specifically be looking at the demographic history of species such as the woolly rhinoceros, woolly mammoth, wild horse, reindeer, bison and musk ox. The main findings from Lorenzen et al (2011) show that climate was a major driver of population changes over the past 50,000 years for certain species such as Eurasian musk ox and woolly rhinoceros. However research from ancient DNA and species distribution models also reveal that the combination of climate and anthropogenic impacts seem to be responsible for the extinction of other species such as Eurasian steppe bison and wild horse. Therefore, it is clear that each species responds in a different way to the effects of climate variability and human intrusion, making it even more difficult to predict past responses to various mechanisms of extinction.
Toward the end of the late Quaternary, beginning around 50,000 years ago, Eurasia and North America lost approximately 36% and 72% of their large-bodied mammalian genera (Lorenzen et al 2011). The two most credible causes of extinction include climate and human impact, and these were assessed by Lorenzen et al (2011) in relation to potential ranges of specific megafauna. The dominate role climate played in extinction patterns are shown in a high loss of species in continents that experienced the most dramatic climate variability. The impact of human encroachment is also shown in patterns of megafaunal decline immediately after initial colonization.
The image below (Lorenzen etal 2011) is a very useful illustration modelling specific species and their changes in distribution over time. This illustration is also effective in showing whether extinction was dramatic or occurred gradually over a long period of time. For example, genetic diversity in bison and musk ox declines gradually from 50,000-30,000 kyr BP, whilst other species such as woolly mammoth and woolly rhinoceros loss of genetic diversity occurred suddenly. It is also evident that Reindeer populations remained largely unaffected throughout the late Pleistocene.
Overall, whilst the results for the model (see illustration above) are useful in showing potential ranges of megafauna over time, this research has shown that it is difficult to make a direct link between climatic change and species extinction. Consequently, causes of extinction for certain species such as woolly mammoth are unclear. The results demonstrate that changes in megafauna abundance are idiosyncratic, with each species responding differently to the effects of climate change, habitat redistribution and human encroachment (Lorenzen et al 2011). Therefore it is highly difficult to suggest a single cause of megafaunal extinction during the Late Pleistocene as evidence remains unclear and deeply contested. In later blogs we will look at the possible explanations behind the disappearance of the wooly mammoth.