A native apex predator limits an invasive mesopredator and protects native prey: Tasmanian devils protecting bandicoots from cats

Abstract

Apex predators can limit the abundance and behaviour of mesopredators, thereby reducing predation on smaller species. We know less about whether native apex predators are effective in suppressing invasive mesopredators, a major global driver of vertebrate extinctions. We use the severe disease‐induced decline of an apex predator, the Tasmanian devil, as a natural experiment to test whether devils limit abundance of invasive feral cats and in turn protect smaller native prey. Cat abundance was c. 58% higher where devils had declined, which in turn negatively affected a smaller native prey species. Devils had a stronger limiting effect on cats than on a native mesopredator, suggesting apex predators may have stronger suppressive effects on evolutionarily naive species than coevolved species. Our results highlight how disease in one species can affect the broader ecosystem. We show that apex predators not only regulate native species but can also confer resistance to the impacts of invasive populations. Apex predators could therefore be a powerful but underutilised tool to prevent biodiversity loss.

Quantifying 25 years of disease‐caused declines in Tasmanian devil populations: host density drives spatial pathogen spread

“…Although the outlook for the wild devil population is undoubtedly more positive than it was a decade ago (McCallum et al 2009), devils are currently well below ecologically functional densities across much of Tasmania. Devil declines have had cascading ecological effects, such as carrion accumulation (Cunningham et al 2018), mesopredator release with effects on small and medium-sized mammals (Hollings et al 2014;Hollings et al 2016;Cunningham et al 2020), and the relaxation of anti-predator behaviours by prey (Hollings et al 2015;Cunningham et al 2019a;Cunningham et al 2019b). In the the online data repository, we provide annual rasters of estimated devil densities from 1985 to 2035, which we expect will be useful for improving our understanding of the ecological effects of devils and identifying thresholds that could provide longer term targets for population recovery.…”

Mesenchymal plasticity of devil facial tumour cells during in vivo vaccine and immunotherapy trials

“…In comparison, DFT2 was identified in 2014 in a small region of South‐East Tasmania and is yet to become wide‐spread 7,11 . Conservation of the Tasmanian devil is considered a priority due to the status of the species as an apex predator and its role as a competitor of introduced pests, such as feral cats 12 . Recent studies have identified a small subset of devils with natural tumour regressions 13 .…”

“…7,11 Conservation of the Tasmanian devil is considered a priority due to the status of the species as an apex predator and its role as a competitor of introduced pests, such as feral cats. 12 Recent studies have identified a small subset of devils with natural tumour regressions. 13 However, these natural regressions remain rare, and to date there has been no sustainable population recovery.…”

Dominant carnivore loss benefits native avian and invasive mammalian scavengers

“…For example, mesoscavengers were attracted to wolf kills yet were negatively associated with wolf density at the landscape scale [19]. Although carcasses are attractive to mesoscavengers, predator avoidance plays an important role in shaping carnivore communities [18, 20].…”

“…Across the southern-temperate continental island of Tasmania (Australia) and its large offshore islands (Fig. 1; total area: 68,401 km), a large-scale natural experiment is occurring due to the severe population decline of the largest extant terrestrial carnivore, the marsupial Tasmanian devil Sarcophilus harrisii [20]. Devils are Tasmania’s dominant scavenger, being both the largest extant terrestrial mammalian carnivore and a specialist, although facultative, scavenger adapted for processing the toughest parts of carcasses [21].…”