Tuesday, 29 November 2011

A study from the other side...(i.e. supporting the human hypothesis)

As I fell I have been maybe a bit bias with my recent entries, I am going to present a study which looks to alternative explanations to the climate change hypothesis for the late Pleistocene extinctions. This study is specifically focusing on a study reporting on the faunal succession from the Tight Entrance Cave in south-western Australia (Prideaux et al 2010)

Archaeological evidence from this study indicates there was a diverse mammal community for at least 100ka up to the earliest evidence of humans at around 49ka. And then within 10 millennia, all larger mammals apart from the gray kangaroo and the thylacine are lost from the regional record. Now this study does acknowledge that there was severe climate change at around 70ka, as determined by stable-isotope, charcoal, and small-mammal records, but it claims this was far before the extinctions. Hence they propose that actually humans played the decisive role in the extinctions, with changes in climate and fire activity only contributing facilitating roles. One of the main reasons for this conclusion is that in the last 5 glacial-interglacial cycles show central southern and south-eastern Australian fauna were identical to their Holocene counterparts and resilient to climate perturbations, so why should this particular transition in climate have wiped out the majority of large mammal populations? Well I think I have probably answered this question before in this blog with Horton’s concentric habitat theory, where a threshold during this climatic transition was reached and hence the mass extinction.

But anyway, Prideaux et al (2010) furthered their investigation by investigating the stratigraphic variation in charcoal concentration, which reflects the fire history of the region and the stable isotopes in aragonitic land snail shells as a proxy for climate change. This evidence found that although the some extinctions between 50-40ka during a dry phase, a lot survived the increased aridity leading to the last glacial maximum. Hence they pose the extinctions cannot be down to climate change alone.
Also the Tight entrance Cave record shows greater bushfire activity in the lead up to the last glacial maximum than in the equivalent climatic phase 100ka before. However, the first indications of regional activity were 20ka before the extinctions, ruling out fire as a main cause of the extinctions. Hence Prideaux et al (2010) turn to human impacts such as hunting and habitat alteration as the primary driver for the extinction, along with the detrimental impacts of the arid climate and the fire regime.

This research is interesting and does point to the other side of the argument over the late Pleistocene extinctions. But it doesn’t change my opinion on the climate change hypothesis being the most likely explanation for the mass extinction. I think most researchers who discount the climate change hypothesis see it in a overly simplistic and linear way. They think because the environmental change in earlier climatic transitions was similar or even more severe than the late Pleistocene extinction that the climate isn’t the answer. But that is simply not the case; the environment is a very complicated system with delayed responses, thresholds and intricate interactions that warrant it a much more complex explanation and understanding as an incredibly powerful mechanism. That’s why I think sometimes the climate is undermined as an explanation for the late Pleistocene extinction in Australia.

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