Abstract
A large component of the anthropogenic biodiversity crisis is the loss of animal species. In response, there has been significant investment in reintroductions of species to their historical ranges. Predation by native and exotic predators, however, remains a barrier to success. Over the past 200 years, Australia has seen the highest rate of mammal extinction on earth, with mammals within a critical weight range (CWR: 35 g–5.5 kg) most affected due to predation by exotic predators. Populations of some threatened species now exist only in Tasmania, offshore islands, or predator-proof sanctuaries. The next critical step is to return native populations outside of predator-free areas, ‘beyond-the-fence’, on the continental mainland. Given our current inability to completely remove exotic predators from mainland ecosystems, how can we achieve successful mammal reintroductions? A potential solution is to drive adaptation of reintroduced animals towards predator-resistance by exposing them to low levels of predation. We propose the concept of a ‘Goldilocks Zone’—the ‘just right’ levels of predation needed to drive selection for predator-resistant native species, while ensuring population viability. We experimentally reintroduced a mammal, the eastern bettong (Bettongia gaimardi), to mainland Australia, 100 years after its local extinction. Using an intense baiting regime, we reduced the population density of the red fox (Vulpes vulpes), the main factor behind the eastern bettong’s extirpation from the continent. Reducing bait take to 15% of previous levels allowed differential survival among bettongs; some surviving under 100 days and others over 450 (~ 4 times longer than some similar trials with related species). Surviving individuals were generally larger at release than those that died earlier, implying selection for larger bettongs. Our results suggest that reducing predation could establish a Goldilocks Zone that could drive selection for bettongs with predator-resistant traits. Our work contributes to a growing body of literature that explores a shift towards harnessing evolutionary principles to combat the challenges posed by animal management and conservation.
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Acknowledgements
We acknowledge and respect the Ngunnawal people, the traditional custodians of the lands on which this work was undertaken. Thanks to Helen Crisp, Kelly Debono, Fred Ford, Suzie Fowler, Margaret Kitchin, Stuart Jeffress, Brett McNamara, Nick Mooney, Katherine Moseby, Nicki Munro, Glen Saunders, Jim Trappe, and Michelle White for providing advice. Thanks to Ollie Orgill, Lisa Steindler, Kym Birgan, Jason Cummings, Karen Williams, Hannah Waterhouse, and Nicole Hill for assistance with the implementation of the project. Thanks to Ben Phillips, Sarah Legge, Adrian Wayne, Joanne McMillan and Tim Andrewartha for providing helpful and insightful comments on earlier drafts of the manuscript.
Funding
This project was supported by the ACT Government, the Australian National University, The Mulligans Flat—Goorooyarroo Woodland Experiment and the ACT Woodlands and Wetlands Trust. The research also received funding from the Australian Government’s National Environmental Science Program through the Threatened Species Recovery Hub to support WB and ME. EB was funded by The Woodlands and Wetlands Trust. ME was partly funded by the Japan Society for Promotion of Science (JSPS) as a Postdoctoral Research Fellow (P19084).
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ADM, WB, TC, CW, DF, SS, TE, MH, AM and IJG conceived the study; all authors contributed to fieldwork; ACT Government staff carried out the fox control and monitoring; ME analyzed the data and prepared the original draft manuscript. All authors contributed to revision of this manuscript.
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Evans, M.J., Batson, W.G., Gordon, I.J. et al. The ‘Goldilocks Zone’ of predation: the level of fox control needed to select predator resistance in a reintroduced mammal in Australia. Biodivers Conserv 30, 1731–1752 (2021). https://doi.org/10.1007/s10531-021-02166-y
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DOI: https://doi.org/10.1007/s10531-021-02166-y