Date of Award

2015

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Natural Sciences

Faculty

Faculty of Health, Engineering and Science

First Advisor

Dr Rob Davis

Second Advisor

Dr Eddie van Etten

Abstract

Invasive predators are major drivers of global biodiversity loss and their impacts may be worsened by other disturbances such as fire. I examined how the fire history of shrublands influences the ecology of feral cats Felis catus, dingoes Canis dingo and their prey species in Western Australia’s northern Wheatbelt region.

A review of the literature revealed that feral cats inhabit a diverse range of ecosystems worldwide, but are generally recorded most often in habitat types characterised by a mixture of plant growth forms close to ground level. Cat habitat use is influenced by predation/competition, prey availability, shelter availability and anthropogenic resource subsidies. Relatively few studies were available for review and the strength of evidence contained within them was generally low, which highlighted the need for more rigorous field studies.

I examined overlap in resource use between cats and dingoes using remote camera surveys and dietary analysis of scats. Both carnivores were recorded in all four major habitat types: recently burnt shrublands (10 to 14 years since last fire), long unburnt shrublands (34 to ~49 years), very long unburnt shrublands (> 50 years), and woodlands. Dingoes and cats preferred woodlands and very long unburnt shrublands respectively, but spatial overlap between the two species was still common. Mean diurnal activity time for feral cats was two and a half hours later than that of dingoes. The diet of feral cats was more diverse than that of dingoes and dietary overlap between the two carnivores was relatively low. Rabbit remains did occur relatively frequently in both cat and dingo scats, but small mammals, reptiles and birds were also common in cat scats, and macropods in dingo scats.

Nine of the 15 prey species studied showed a preference for either recently burnt or long unburnt shrublands. Two small mammals and three reptiles were most abundant in recently burnt areas, while the abundance of one small mammal and three reptiles was highest in long unburnt areas. Using giving up density experiments, I showed that rodents exhibited differential foraging behaviour in the two vegetation fire ages. The rodents foraged for longer in sheltered compared to open microhabitats, but this pattern only occurred in recently burnt, not long unburnt shrublands, probably because the higher density of understorey vegetation in recently burnt areas provided the rodents with extra cover to hide and escape from predators.

I also developed a new framework for conceptualising interactions between invasive predators and other ecological disturbances, such as fire, habitat fragmentation, and top -predator decline. The impacts of invasive predators can be classified as either functional (density -independent) or numerical (density -dependent), and they interact with other threats through both habitat -mediated (fire, grazing, land clearing) and community -mediated (top -predator decline, altered prey populations, anthropogenic resource subsidies) interaction pathways. The key findings of this thesis show that both old and young shrublands can be suitable habitat for feral cats; predator -prey dynamics are influenced by successional habitat stages; small mammals show behavioural, as well as population -level responses to fire; and that invasive predator management is likely to benefit from addressing multiple threats in unison.

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