Competitive interactions among invasive mammalian predators in New Zealand

Background/Question/Methods

Stoats (Mustela erminea), ferrets (Mustela furo) and feral cats (Felis catus) were introduced to New Zealand in the late 19^thcentury as an early attempt at biological control. These predators have subsequently had a devastating impact on the naive native wildlife, which evolved in isolation for over 70 million years. Trophic interactions between this mammalian guild has not been extensively studies, but empirical evidence suggests that interference competition will influence the structure of ecological communities, with direct consequences for native species survival.

We tested the behavioural responses of 18 wild captured stoats to the presence of both a feral cat and ferret. Stoats were released individually into an outdoor arena and segregated from one of the larger predator on each trial night. A stoats’ perception of risk was assessed by comparing behaviour at a high-risk versus low-risk food patch. The second phase of the research tested the mechanism by which predator avoidance occurs. We exposed stoats to the body odour of the two larger guild members, one novel predator (African wild-dog) and a control scent. We analysed changes in foraging behaviours and used these as surrogate measures of fear.    

Results/Conclusions

Stoats were found to reduce harvesting, increase vigilance and increase spatial avoidance at the high-risk patch containing either of the larger predators.  Results clearly illustrate that stoats alter their foraging behaviour due to interference competition. In the second phase of the research, stoats were found to increase levels of vigilance when they encountered the odour of ferrets and cats. However, contrary to our predictions, they did not avoid or reduce harvesting at the food patches containing the scent of the larger guild members. We conclude that although stoats avoid the larger predators, due to the real risk of an attack, the predator’s scent is insufficient to produce the same responses. Predator odour alerts a stoat to the historic presence of a dominant competitor and the increase in vigilance improves the probability of a stoat avoiding a lethal interaction.

Mustelidae species are of special interest to conservation, as they have members on both the IUCN red list of threatened species and the list of the world’s worst invasive species. Understanding trophic interactions is particularly important in New Zealand, where invasive species control may alter the ecological balance to the benefit of one predator and to the determent of its preferred prey.