Lessons from how pumas and wolves interact in North America can be applied here in New Zealand, as we strive towards a predator-free 2050.
Dr Heiko Wittmer has looked at what happened when wolves were reintroduced to Wyoming's Grand Teton National Park. The wolves had a negative effect on the pumas in the park and that led to a much more balanced ecosystem.
Heiko tells Summer Times that despite being a large and wild park, it had lost its wolf population due to culling in the early 20th century.
“Since then they have been missing and that has led to some drastic changes in the ecosystem.”
He says the nearby Yellowstone National Park was first to re-introduce wolves in the 1990s and they found that it dispersed the elk population – their prey – and had a major benefit to the ecosystem.
Introducing wolves to Grand Teton National Park also provided another interesting element to study.
“We were more interested in how the return of the wolf would affect another apex predator in the system, and that’s the puma. That was the focus of our study, trying to understand why we saw threefold decreases in the puma population when wolves naturally recolonised the Grand Teton National Park.”
There were three elements for them to explore in trying to explain the loss of puma, one was that people hunt puma for sport, another was the decrease of elk due to the uptick of wolves, and another was the competitive behaviour between the two apex predators.
He says New Zealand aiming for a predator free environment could have unintended consequences for the ecosystem.
“I think we should have a more careful look at it.”
Far from having pumas and wolves running around our forests, Wittmer says the species highest on the food chain here are cats, stoats, and rats.
“Removing those apex predators has had a real benefit from a conservation perspective, but what we’re going to propose to do is remove some of them, but leave some species behind, for example mice.”
He says that rats, cats, stoats and mice have a competitive relationship with one another and that attempting to remove them all could mean one becomes dominant.
While mice becoming more prevalent would have less of an impact on birds, it could be harmful to native invertebrates such as wētā and weevil.
“We tend to forget about them and are very much focused on our bird life, for obvious reasons, but let’s not forget there are other native species in the system and those are going to affected by mice.”
Wittmer says we need to be aware of these relationships and be cautious about making drastic changes to the ecosystem.
“We can’t continue to say this is unexpected anymore because anytime we remove or introduce a species into a system, it’s going to have relationships with other species and they are often long established.”