Madison Reporter

Researchers from the University of Wisconsin–Madison have found that the reintroduction of wolves to Isle Royale has had only temporary effects on other carnivores, with human activities playing a more significant role. The study, published in Frontiers in Ecology and the Environment, utilized DNA from foxes’ and martens’ scat and hair to analyze their locations and diets before and after the wolves' reintroduction.

Mauriel Rodriguez Curras, who conducted this research as a graduate student under Professor Jonathan Pauli, stated, “We had this really amazing opportunity in Isle Royale — where we had data before this large carnivore reintroduction and then following the reintroduction of wolves — where we could look at how these effects within carnivores are taking place, and how they shift.”

Isle Royale is a remote island in Lake Superior known for its isolated ecosystem. Wolves first arrived on the island in the 1940s via an ice bridge but dwindled to just two by 2018 due to inbreeding. In 2019, 19 wolves were introduced to restore balance.

Fieldwork involved extensive hiking to collect hair samples using traps and swabbing scat for DNA analysis back at UW–Madison. The researchers identified individual foxes or martens from these samples and reconstructed their diets through carbon and nitrogen ratios.

The study categorized wolf effects on other carnivores into three phases: absence (before reintroduction), establishment (first year post-reintroduction), and coalescence (when wolf packs formed). During establishment, foxes moved closer to campgrounds while martens expanded their territory. By 2020, with established wolf packs, both species returned to pre-reintroduction behaviors.

“The rewilding of these species is an important move that conservation biologists are making to try and reweave the fabric of ecosystem function,” said Pauli. “But I think the point is that when we do this reweaving of communities, unexpected things happen.”

Human visitors significantly influenced these interactions by providing food sources near campgrounds. This finding underscores humans' impact even in remote areas like Isle Royale.

Rodriguez Curras and Pauli's work highlights how species interact with each other and humans, offering insights for future conservation efforts. Their research was supported by grants from the US National Park Service, the National Park Foundation, and a fellowship from UW–Madison SciMed Graduate Research Scholars.