University of Wisconsin-Madison researchers found in May 2024 the effects of wolf reintroduction on Isle Royale to be temporary and particularly impacted by human recreation, despite being one of the least visited National Parks.
Mauriel Rodriguez Curras and UW-Madison ecology professor Jonathan Pauli collected DNA from foxes’ and martens’ scat and hair to investigate spatial, dietary and behavioral habits before wolves were introduced, within the first year of introduction and as packs coalesced on the island.
Isle Royale is a remote island located in Lake Superior, Michigan. It’s a relatively simple ecosystem with fewer species — including moose, beavers and squirrels — making it easier to pinpoint the effects of the wolf introduction, researcher Curras told The Daily Cardinal.
Nineteen wolves were reintroduced to the island in order to stabilize the ecosystem after the wolf population dwindled to an inbred father-daughter duo in 2018. Likely first coming to the island over a 15-mile ice bridge on Lake Superior, the population was once as high as 50 in several packs.
Traditionally, ecologists study predator-prey relationships, but this study instead focused on predator-predator relationships, according to Curras.
“Relationships between predators and prey [can be] quantified just by counting the numbers of predators and the number of prey on a landscape, but the interactions between predators and predators are more behavioral, they’re cryptic,” Curras said.
Data collection involved hiking 15 to 20 miles a day, often alone, to check traps for hair as well as swab and collect any found scat. One type of hair trap was a PVC pipe tube with brushes on either end. Scientists placed bait in the center, and the animal would crawl through, catching hair against the brushes.
The study’s limitations included the small size of the ecosystem and the short time period — 2020 to 2022 — as these patterns may not be replicated in mainland systems.
Scientists also worked with the National Parks Service and scientist Mark Romanski, who specialized in wolf reintroduction.
Back in the lab at UW-Madison, Pauli and Curras extracted DNA from the samples and matched it to previously identified individual capture histories, allowing them to identify the individual fox or marten.
From these measurements, they categorized the habits of the foxes and martens into three phases related to the wolves reintroduction: absence, establishment and coalescence.
In the establishment phase, wolves wandered the island more as individuals. This caused foxes, who are at risk of competition or being killed by wolves, to cluster closer to campgrounds. In some cases, their diets doubled to 80% human food as compared to an average of 40% human food before the wolves were introduced.
Martens are typically limited spatially by foxes, since foxes kill and compete with martens, so they spread out as foxes moved closer to campgrounds. Martens typically stick to more densely wooded areas.
There was a slight increase in the marten population as they spread out and competition with foxes decreased, but there was no major change in the fox population, which was most surprising to Curras.
“[Foxes] were using more human foods in their diet, and we think that buffered some of the numerical responses that we might have expected to see from wolves,” Pauli said.
Some foxes also subsidized with carrion meat left from wolves, but this involved greater risk than interacting with humans for food.
The dietary shift of foxes and the lack of population change demonstrates how flexible foxes are, Curras said. They're one of the most widely distributed carnivores, living in deserts, rain forests and even cities.
Despite these effects, the scientists found that once the wolves coalesced, behaviors returned to the baseline they observed before the reintroduction.
“Scientists think if we can restore apex carnivores, all of these ecological cascading effects will come about and things will return to how they were historically,” Pauli said. “This work shows these repatriation events are important, but some of the effects that we're looking for may only be temporary.”
Mary Bosch is the photo editor for The Daily Cardinal and a first year journalism student. She has covered multiple stories about university sustainability efforts, and has written for state and city news. Follow her on twitter: @Mary_Bosch6
