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Abstract
Alien predators have on average twice the impact on native prey populations than do native predators, and are a severe threat to wildlife globally. Manipulation experiments can be used to quantify the impact of an alien predator on its prey population/s, but unless the results are compared to benchmarks, it is unclear whether this impact is indeed greater than that of a native predator. Here we use the Australian garden skink Lampropholis delicata and alien black rat Rattus rattus to test if black rats are an additive source of predation for the skink, and to judge whether the effect size of rat-impact on the skink represents that of an alien or native predator. We used replicated experiments to exclude black rats at local and landscape scales to test how rats affect skink activity and trapping frequency. Both manipulations had positive effects on skinks, however, the population-level effect size was lower than that described for alien predators but similar to that expected for native predators. We suggest that Australian skinks may respond appropriately to predatory alien rats because they coevolved with endemic Rattus species. This adds novel insights into the varying levels of impact that alien predators have on native prey.
Highlights
Alien predators have on average twice the impact on native prey populations than do native predators, and are a severe threat to wildlife globally
Salo et al.’s2,6 meta-analyses provide benchmarks for the effect sizes of the impacts of alien and native predators. We suggest that these benchmarks can be used to categorize whether predator impacts align with those of an alien predator or a native predator, and allow assessment of exactly where the impact of a particular alien predator lies along the native-alien continuum
All predators have some measurable impact on their prey populations, and alien predators appear to have, on average, twice the impact of native predators[2]
Summary
Alien predators have on average twice the impact on native prey populations than do native predators, and are a severe threat to wildlife globally. We used replicated experiments to exclude black rats at local and landscape scales to test how rats affect skink activity and trapping frequency Both manipulations had positive effects on skinks, the population-level effect size was lower than that described for alien predators but similar to that expected for native predators. Alien rodents are among the world’s worst invasive predators and have caused global population declines of native birds[7,8] and invertebrates[9,10,11], as well as extinctions of mammals[12] Owing to their size, small reptiles should be at risk from alien rodents, current understanding of their responses to any alien predators is limited. There are anecdotal accounts of reptile recovery or range expansion after removal of alien rodents (e.g. refs 13, 18–21), but the precise role of rodents in these cases is often confounded by removal of other alien species, e.g. ref. 19, or lack of replication, e.g
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