Self‐organised instability and megafaunal extinctions in Australia

It is generally known that during the Quaternary there were wide spread extinctions of fauna on all continents except for Antarctica. The coinciding of these extinction events with the arrival of humans on each of the respective continents has led to the hypothesis that humans hunted this fauna into extinction (Flannery 1994). Termed the blitzkrieg or overkill hypothesis (Martin 1984), such was invoked by Flannery (1994) to explain the extinction of the megafauna in Australia. However, the applicability of the overkill hypothesis to Australia was brought under intense and serious scrutiny due to problems with the timing of the extinctions and human arrival (Grayson 1990), and the lack of any mass-kill sites such as has been found in New Zealand and North America (Owen-Smith 1989). Opponents to the human caused extinction have often cited the fluctuating climate characteristic of the Pleistocene as the causal agent in the demise of the Australian megafauna (Horton 1977). Problems with correlating extinction events with severe climatic conditions have produced incongruence in the climateinduced hypothesis (Flannery 1994). Consequently, a third hypothesis, the anthropogenic disruption hypothesis, which states that Aboriginal burning modified habitats enough to bring about a change in the ecology of the megafauna and their eventual demise, has been put forward (Miller et al. 1999). Due to the fact that the megafaunal extinction debate in Australia has reached a certain stalemate relative to the debate in other regions of the world, a rather different, if not heuristic, hypothesis is proposed here to stimulate an alternative line of inquiry. The hypothesis has been largely developed from recent advancements in the study of system complexity. I propose that an increase in immigration of fauna from south-east Asia and speciation of the existing local fauna in response to the increasing aridity of the Pliocene led the faunal assemblage of Australia to a level of self-organised instability, as defined by Sole et al. (2002a). The arrival of humans into Australia increased significantly the level of connectivity between the faunal elements in the Australian faunal system. Subsequently, the fauna of Australia was inherently susceptible to an extinction event. The purpose of this paper is to outline the logic behind this hypothesis, from here to be termed the self-organised instability (SOI) hypothesis of megafaunal extinctions, and the conditions that allow it to be applicable to Australia.