Wednesday, January 4, 2012

Davis has Oz wrong

In response to Marris citing it, I am now reading Mark A Davis “Researching Invasive Species 50 Years After Elton”. Davis is saying specifically in the case of Australia that: In Australia, non-native species have been reported to have contributed to the extinctions of some native mammals (see Finlayson 1961; Kinnear et al. 1998). However, the fact that declines in native species typically began decades before the introductions of species such as cats and foxes (often reputed to be the causes of extinctions), and the fact that species introductions are usually associated with other types of anthropogenic change that are believed to have contribute to the declines (for example land use change), it is difficult to ascribe extinctions of Australian mammals exclusively to no-native species (Abbott 2002; McKenzie et al. 2007.

Well that doesn’t accord with my understanding. Cats arrived with the First Fleet – the first settlement of Australia, as did cattle, which also soon ran wild. So I am not sure how “declines in native species typically began decades before the introductions” could work. In Australia’s case the introduction of species came early and non-native species spread quickly. We have seen waves of extinction in mammals since the arrival of Europeans – the latest of which is going on in the north at the moment with the disappearance of the bilby and other like sized animals.

A lot hangs on the word exclusively. Define it narrowly and  anything can be justified. Little if anything has a singular cause. The smaller mammals were not just killed by cats but had their habitats destroyed as farmers cleared bush litter, and the ground hardened by the hooves of introduced cattle. (Are cattle a land-use change or an invasive species?)

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