Saturday, 7 January 2012

The last blog entry!

So as you may have already deduced, I think that the changing climate was the cause of the late Pleistocene mass extinction in Australia.

So humans arrived around 48,000 years ago, some even claiming up to 60,000 years ago, the majority of species disappeared between 26,000 and 15,000 years ago and the LGM set in around the same time at around 26-20,000 years ago. So even looking at these dates, it is obvious there is correlation between the climate and species extinction, not the arrival of humans.

Considering the human hypothesis, there are just too many questions left unanswered. Mainly, how did the megafaunal species and humans co-exist for so long without extinction? Could it just be coincidence the extinctions occurred when the climate saw its most severe transition? Why is there a lack of archaeological evidence with both human and megafaunal remains? Were the small indigenous human populations present really large enough to caused such a large scale extinction? All of the answers to these questions definitely disprove the 'blitzkrieg' model and cast the human hypothesis in much doubt.

Considering the climate change hypotheses, the story seems to make more sense. As I have presented in this blog, there is plenty of evidence for increased aridity. Dodson (1989), Guthrie (1984), Jones and Bowler (1980) and more recently Hesse et al (2004), Mooney et al (2011) and Murphy et al (2011). All of these studies and others from this blog illustrate the continuing aridity in Australia, and the result of deteriorating ecosystems and declining habitat areas.

As I've stated through this blog, I think that Horton's (1984) explanation for the extinction is the most accurate. The concentric habitable areas explains why the extinctions targeted the larger mammals, why they happened over quite a prolonged period but mainly throughout the LGM and why the extinctions were so extensive.

I'll just go over some of the main theories and how they could fit into the climate change hypothesis in Australia. Although it is almost impossible to know which one is completely correct, I think they all provide some additional explanation onto Horton's (1984) hypothesis as for the reason of this extraordinary event. Forster’s (2003) ‘self organised stability’ theory explains why as the habitable areas became smaller as aridity took a steep incline, species composition became less diverse as some were made extinct. Hence the remaining species became more inbred resulting in more extinctions and enhanced vulnerability to environmental changes. In this sense, Guthrie’s (1984) ‘mosaic nutrient hypothesis’ can also be used, as the vegetation within these concentrated areas became more affected by environmental change, the plant diversity decreased. This explains why more and more areas were becoming less inhabitable as the aridity increased. Also even though Ficcarelli’s (2003) hypothesis was applied to Ecuador, the ‘habitat loss hypothesis’ also comes into play here. With increased aridity in Australia, environmental thresholds were crossed and parameters bypassed. This means the demise of many vegetation types and the decline of many habitats leading to extinction. 

And so there you have it, after extensive reading and writing for this blog, that's what I've come up with! Hope you agree!

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