Top predators play important roles in structuring ecological systems where they have strong interactions with other predators and prey species. Their loss can dramatically shift ecosystems to new states and result in a competitive release of smaller invasive predators, such as feral cats (Felis catus), that may have detrimental impacts on key prey species. In a tragic natural experiment, Tasmania’s now top predator, the Tasmanian devil (Sarcophillus harasii), is rapidly declining across Tasmania due to a novel facial tumour disease and recent studies suggest that feral cat populations are increasing in these areas. While studies suggest Tasmanian devils may limit populations of feral cats, no study has directly investigated the interactions between feral cats and Tasmanian devils.
This project aims to investigate the competitive interactions between the Tasmanian devil and the smaller feral cat, to determine if they may reduce the population of feral cats. As part of a conservation initiative in response to DFTD, twenty-eight Tasmanian devils were introduced to Maria Island, located off the east coast of Tasmania, to establish a wild population of free living animals. Maria Island, often referred to as Tasmania’s Eden, has seen multiple vertebrate species introductions over the past 50 years including cats, black rats (Rattus rattus), house mice (Mus musculus) and native herbivores that have all contributed some influence on the island’s fauna and flora.
We used GPS collars on feral cats to understand more about their habitat use in response to an increasing devil population. Similarly, remote camera surveys were conducted bi-annually in summer (“peak prey”) and winter (“low prey”) on Maria Island and an adjacent control site (with a low, stable devil population) to identify individual cats (for population estimates) and test for changes in activity times and distribution.
Results/Conclusions
Our results suggest that devils may limit populations of feral cats, with preliminary results showing steady declines in the cat population. Further statistical analyses are needed to confirm if these findings are robust but current findings suggest that competition for resources may be responsible for these declines. Similarly, there is evidence that cats have shifted their distribution in response to devils, occupying higher elevations, where devils are less common.
This bold conservation strategy has been highly successful in conserving the future of the Tasmanian devil and our results aim to increase our understanding of the Tasmanian devil’s role in structuring ecosystems and potentially limiting invasive species, such as feral cats.