Monday, 3 December 2012

Some Examples of Extinct Megafauna in relation to Climate and Human Impacts

I recently found this interesting article by Lorenzen et al (2011) that links specific species responses during the late PLeistocene to climate and humans. In this blog I will look at the various suggestions put forward by Lorenzen et al (2011) and assess whether strong conclusions can be made between time of extinction in relation to climate variability and/or human colonization.
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.


  1. Hi,

    What might be interesting to know is how closely related modern species are responding to climate change. For example reindeer and oxen, do they have population declines which appear to correspond to current climate change? And if this is true in the present, this could mean past climate changes could be inferred as having a greater effect on megafauna extinctions.


  2. Hey Harriet,

    Really good point! It would be very interesting to know how modern day species are responding to climate change. I believe that you are looking at individual species and reasons why they are threatened/facing extinction. In this course, a friend of mine is looking at the effects of global warming on species on the ocean (see Saving Nemo blog). However there are some problems with relating present day studies to the past. Firstly, in present day studies man is mostly responsible for climate change through bringing about global warming. In the past, this was not so as climatic changes were mostly driven by natural processes. Secondly, climate changes were more dramatic in the past. Shifts from interglacial to glacial conditions were more extreme compared to gradual warming trends we see today. Such dramatic shifts in temperature could be seen to be responsible for causing such extensive extinctions, whilst current day losses are much smaller in comparison. The loss of oxen and reindeer has occurred, but linking this to climate is controversial. Past conditions were very different to that of todays in terms of climate, and the impact of man. Therefore by relating present situations to the past might not be the most accurate and reliable means of inferring reasons for megafaunal decline.

    hope this helps