Monday, 12 December 2011

The 'habitat loss hypothesis'...

So I realise that in my glossary I have listed a concept called ‘habitat loss hypothesis’. Thus, in this blog I am going to address this theory through the study by Ficcarelli et al (2003) carried out in the Ecuadorian coastal regions. Now I know that this obviously isn’t Australia, but it would be interesting to see if this theory could apply to Australia.

Now, it’s actually quite funny, in Ecuador during the Late Pleistocene, the climate went from very arid to very humid over 2000 years. This change in climate most importantly caused a shift in vegetation composition. The increased moisture availability caused the increased density of vegetation cover, the creation of fluvial barriers and transformed the refugia into lethal traps for large megafaunal species. These species, mainly the mastodons, ground sloths and equids, were already under intense biological stress, as their habitats had already decreased dramatically. The humid conditions caused linear erosion and river down cutting, also impacting the environment more dramatically. Ficcarrelli et al (2003) do not believe human impacts were a primary force in the extinction in Ecuador, although they could have had a minor local impact. However, Ficcarrelli et al (2003) do not provide an answer as to why extinctions this extensive did not occur during the glacial / interglacial transitions earlier in the Quaternary period. However, they do allude to an explanation quite similar to Horton’s (1984) concentric habitat hypothesis (described in an earlier blog entry). They give the fundamental parameters of aridity, humidity and geographical factors as prime reasons. Alternations between cooling and warming continued at differing intensities during transitions in climate. But during the last transition causing the mass extinction, a lot of these parameters will have been emphasised and thresholds were crossed, altering the vegetation completely and causing mass extinction.

So I found this article quite interesting, but what does it mean for Australia? Well, let’s apply it, but well the opposite way round. The climate in Ecuador went from arid to humid conditions, but in Australia, as already discussed, the climate went from wet to extremely humid. But the theory still stands, vegetation shifts caused by the climate leave species without food, shelter and habitat. In Australia, it has already been discussed in earlier blogs that there was a huge shift in vegetation to arid / semi arid shrubland and grassland causing species to first migrate but eventually become extinct Dodson (1989). So I think this theory is really interesting and applies to Australia, even though it is based on a completely different continent!

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