Abstract
The control of selected invasive mammalian predators has become common in New Zealand’s urban habitats. However, urban ecosystems are complex, and it is not often clear how the interactions between invasive species and native fauna might change when some, but not all, invasive predators are controlled in our cities. Ecological processes such as meso-predator and competitive release between pest species may result in unexpected or unwanted outcomes from selective predator control. This thesis aims to research whether selective predator control of rats affects members of the non-target mammalian predator guild in an urban environment.
In Chapter 2, I performed a Before-After, Control-Impact study to investigate whether predator control of rats in urban Dunedin impacts the predatory behaviour (prey composition and predation frequency) and home range, of domestic companion cats. To collect cat predation and home range data, domestic cats were fitted with video cameras and GPS units and cat owners were asked to keep a log of prey brought home by cats. During the same period, rat control took place in the treatment area and was withheld from the non-treatment area. I found that after rat control, the relative abundance of rats decreased, however, this did not affect the behaviour of domestic cats. Cats that caught rats pre-rat control continued to do so post-rat control, and there was no evidence of cats switching prey or changing home range.
In Chapter 3, I analysed nearly four years of invasive mammalian monitoring data from City Sanctuary, an urban pest control organisation in Dunedin, New Zealand, to detect the residual relative abundance of rats, and (non-target) mice and hedgehogs, post-rat control. I found that urban Dunedin's overall rat tracking rate was very low. The relative abundance of rats was lower post-rat control, however, tracking rates of mice and hedgehogs remained unchanged.
My findings suggest that the suppression-only regime in Dunedin, common across New Zealand’s urban areas, is making little difference to the number of, and interactions between, cats, mice, rats, and hedgehogs in urban centres. In cities with a similarly low density of rats as Dunedin, rat suppression may have little effect on non-target predators or native wildlife.