Impact of exotic generalist predators on the native fauna of Australia

Abstract

This paper reviews the impacts of three species of introduced mammalian predators on native fauna in Australia. The feral cat Felis catus, introduced over 200 years ago, is linked with early continental extinctions of up to seven species of mammals, regional and insular extinctions of many more species of mammals and birds, and the failure of management programs attempting to reintroduce threatened native species to parts of their former ranges. Evidence for cat‐impact is largely historical and circumstantial, but supported by observations that afflicted native species are, or were, small (<200 g) occupants of open habitat and hence likely to be especially vulnerable to cat predation. The red fox Vulpes vulpes was released successfully in 1871. Its subsequent spread into all except parts of arid and tropical Australia coincided with local and regional declines of medium‐sized (450 – 5,000 g) mammals, birds and chelid tortoises. The fox has also created recent failures of many management attempts to recover threatened native species. Unequivocal demonstration of fox‐impact has been obtained in removal experiments, especially on rock‐wallabies Petrogale lateralis. The dingo Canis lupus dingo, introduced 3,500–4,000 years ago, probably caused the extinction of the thylacine Thylacinus cynocephalus and Tasmanian devil Sarcophilus harrisii on mainland Australia. It effectively suppresses extant populations of large mammals, such as kangaroos, and emus, over large areas. Impacts of all three predators are wrought primarily by direct predation. Negative impacts appear to be increased in spatially fragmented forests where native species are restricted to remnant vegetation, and in arid landscapes when native species become restricted temporarily to scattered oases during drought. Alternative prey, especially rabbits Oryctolagus cuniculus, enhance negative impacts on native species by supporting large populations of the predators. It is concluded that feral cats and especially foxes have major negative impacts on certain small and medium‐sized native vertebrates in Australia, whereas dingoes have major negative impacts on large species. Dingoes could have positive effects on smaller native species if they significantly suppress populations of foxes and cats. Further quantification of both the direct and indirect impacts of the three predators on native fauna is needed, and should be obtained from experimental field studies.

Disease and the dynamics of extinction

“…For example, Western Australia has recorded a large number of extinctions and dramatic range contractions among mammals since European settlement (of the 72 non-flying mammals present on the Western Australia mainland in 1900, 11 are extinct and 20 have experienced major declines [36]. These declines are usually attributed to predation by European red foxes and domestic cats [37,38]). Abbott [39] describes nearly 50 first-hand reports from between 1840 and 1920 of disease (possibly mange) causing large-scale mortality amongst native mammals and reports declines prior to the arrival of the red fox in Western Australia around 1910 [38].…”

“…These declines are usually attributed to predation by European red foxes and domestic cats [37,38]). Abbott [39] describes nearly 50 first-hand reports from between 1840 and 1920 of disease (possibly mange) causing large-scale mortality amongst native mammals and reports declines prior to the arrival of the red fox in Western Australia around 1910 [38]. He also suggests that there is evidence of a spatial trend in declines, consistent with the introduction of disease somewhere in the northwest.…”

Ecology and Conservation of a New Carnivorous Marsupial Species: the Silver-Headed Antechinus (Antechinus argentus)

“…Ongoing work should specifically examine the impacts of these species on A. argentus. Nevertheless, the links between the declining Australian mammal fauna and both predation by introduced carnivores (Dickman, 1996) and grazing by introduced herbivores (Legge et al, 2011a) are well documented. It is recommended that control measures be substantially intensified for feral animals at Kroombit Tops -particularly cats, cattle, horses and pigs as they are almost certainly having a detrimental effect on A. argentus.…”

“…Climate change is predicted to increase the frequency and intensity of wildfires, further exacerbating the risk (Lucas et al, 2007). With this comes an additional threat, especially for small and medium-sized mammals: increased predation by invasive carnivores (Dickman, 1996). Feral cats in particular can travel large distances specifically to hunt within a recently burned area (Leahy et al, 2016).…”

“…In particular, feral cats (Felis catus) have been shown to travel large distances to reach recently burnt habitat, amplifying predation on exposed native species in the absence of sufficient cover (Dickman, 1996, McGregor et al, 2014, McGregor et al, 2017. Recent evidence has linked the declines of small mammal species with these amplified feral predation effects due to fire, as well as the effects of grazing by introduced herbivores (Legge et al, 2011a While the approach of the present study emphasised vegetation composition, we suggest that future research focus on structural habitat elements such as the size and shape of vegetation, for example the diameter and leaf density of grasstree crowns.…”