Impacts of introduced mammalian predators on New Zealand’s alpine fauna

Alpine zones are threatened globally by invasive species, hunting, and habitat loss caused by fire, anthropogenic development and climate change. These global threats are pertinent in New Zealand, with the least understood pressure being the potential impacts of introduced mammalian predators, the focus of this review. In New Zealand, alpine zones include an extensive suite of cold climate ecosystems covering c. 11% of the land mass. They support rich communities of indigenous invertebrates, lizards, fish, and birds. Many taxa are obligate alpine dwellers, though there is uncertainty about the extent to which distributions of some species are relicts of wider historical ranges. The impacts of introduced mammalian predators are well described in many New Zealand ecosystems, though little is known about the impacts of these predators on alpine fauna. Here we review the importance of alpine habitats for indigenous fauna and the impacts of introduced mammalian predators; and develop a conceptual model explaining threat interactions. Most evidence for predation is anecdotal or comes from studies of species with wider ranges and at lower altitudes. Nevertheless, at least ten introduced predator species have been confirmed as frequent predators of native alpine species, particularly among birds and invertebrates. In the case of the endangered takahe (Porphyrio hochstetteri) and rock wren (Xenicus gilviventris), stoats (Mustela erminea) are primary predators, which are likely to be impacting significantly on population viability. We also document records of mammalian predation on alpine lizards and freshwater fish. While the precise impacts on the long-term viability of threatened species have not been evaluated, anecdotal evidence suggests that predation by mammals is a serious threat, warranting predator control. Future research should focus on predicting when and where mammalian predators impact on populations of indigenous fauna, furthering our understanding of the alpine predator guild particularly through adaptive management experiments, and exploring interactions with other threats.