Interspecific competition and olfactory communication between New Zealand’s invasive predators: unravelling and exploiting stoat behaviour for conservation

Abstract

Stoats (Mustela erminea), feral cats (Felis catus) and ferrets (M. furo) were introduced to New Zealand as agents of biological control and have subsequently decimated populations of many native species. Although the detrimental impacts of these predators are unequivocal, the potential limiting factor of competition among these invasive species is less well understood. Predator demographics can be influenced by several factors such as resource-consumer interaction, facilitation and mutualism, as well as the mechanisms that are the focus of this thesis - competition and predation. I investigated the consequences of interference competition and olfactory communication on the distribution and behaviour of the focal species (stoat), in a series of macrocosm and field experiments. Following a general introduction, Chapter 2 describes pen trials that examine changes in stoat foraging behaviour based on the perceived risk posed by larger predators (cats and ferrets). Olfaction, the dominant sense of many mammals, may mediate trophic interactions by allowing subordinate species to assess the risk of encounter. Chapter 3 therefore examines the importance of interspecific olfactory communication and quantifies behavioural changes of foraging stoats when they encountered the odour of apex predators. Chapter 4 tests whether behavioural responses of wild-caught stoats’ are consistent with observations made in the macrocosm, and evaluates the importance of results for conservation. Finally, Chapter 5 investigates whether niche partitioning facilitates invasive predator coexistence and a removal experiment tests the responses of stoats to changes in the densities of larger predators. The thesis concludes with a general discussion and suggestions for future research. Although New Zealand is the main focus, my results may have worldwide conservation applications. Understanding interactions among invasive carnivores, and the communication mechanisms that maintain predator assemblages, is critical for native species protection in invaded ecosystems.