I’m quite conscious that I’m coming to the end of my blog now, so I want to make sure that I am tying any lose ends. One of these lose ends is the ‘self organised instability’ hypothesis posed by Forster (2003). I mentioned it in the glossary and I think I should explain it so that I have covered all theories applied to the late Pleistocene mass extinction in Australia.
So basically this theory is saying that the in any given area, the resident species number will reach a certain amount and be maintained through immigration or the breeding of new species (speciation). In these systems, extinction results from an increase in the amount of interaction between species as the number of different species increases, hence instability is acting as a barrier to prevent further diversification. Meaning the feedback of the system incorporating immigration, diversity, interaction and extinction leads to self organised instability of an ecological system.
Signs of intense interaction are seen in the overall ecology with many forms of competition, predation, parasitism and mutulism. In fact most of the interaction is found in the form of co-operation between species and human populations. For example, in the Blue Mountains of Sydney, Aborigines may have consumed no less than 72 plants, 45 mammals, 235 birds, 6 fish, 16 reptiles, 29 frogs and numerous invertebrates (Merriman 1993).
Forster also tries to give evidence of a period of speciation and immigration that had to have occurred prior to the extinction for this theory to stand. Figure 1 visually shows how increased immigration could have caused increased diversity, interaction and finally extinction. To prove immigration levels were high, Forster (2003) gives the example of the Rodentia mammalian, who immigrated from south – East Asia and were the first indications of terrestrial placental mammal in Australia. Many species migrated to Australia during the Pleistocene, increasing speciation and extinction and enhanced diversity. Now the arrival of humans may have pushed the ecological systems into a super-critical state where extinctions occurred quite easily, their broad generality enhanced speciation and interaction and could have led to extinction. Hence Forster (2003) is posing here that actually the mere presence of humans in Australia caused the mass extinction. So this hypothesis has no need to rely on the ‘overkill hypothesis’ or the ‘blitzkrieg model’, it was just the increase in interactions caused increased speciation and hence extinction.
|Figure 1: How immigration could have led to extinction in the 'self organised instability' hypothesis.|
Now to me, this theory seems very vague and I don’t think enough factors have been considered. The physiology and biology of different species has not been considered here, and Forster (2003) says himself that the hypothesis is based on one solitary case study from the Hawaiian avifaunal study of Keitt and Marquet (1996). There is very little solid relevant evidence given here and it seems all a bit too theoretical for me. We have no detailed evidence of the historical, biological or ecological traits of the megafauna that went extinct, or even of those who didn’t, so can we realistically base a theory on such little evidence? I don’t think so. We need far more fossilized and archaeological evidence to even begin to prove this theory, which we definitely don’t have at the moment and possibly will never have in the future. We have no explanations as to the different immigration patterns in and out of Australia in the late Pleistocene and we have no information on the speciation patterns either. We don’t even have reliable dating records to tell us the exact dates of the extinctions in Australia, so to be honest I just don’t think proving this hypothesis is feasible. To me it just seems very ungrounded with very little if any evidence to support it, hence I don’t think it is credible enough to consider as a possible explanation to the late Pleistocene extinctions in Australia.
Because not available online:
Merrimann, J. (1993) 'Difficult rocky, sandy, stoney, flowery: Aboriginal ecology in the Blue Mountains', in Stockton, E. (ed.), Blue Mountains dreaming: the Aboriginal Heritage, Three Sisters Productions: page 82–113.