An island colonized by wolves gives new insights into predator-prey relationships

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Sarah Hoy spends the winter in a small cabin on a remote island covered in snow and colonized by wolves.

Drinking water comes from a hole in the ice of Lake Superior, which surrounds the island. A generator provides a few hours of electricity for the laptops. A wood-burning stove provides warmth.

Isle Royale is the ideal place for a researcher.

The 45-mile-long piece of land, belonging to Michigan, offers some of the most interesting terrain for researchers examining the functioning of natural ecosystems, and since 1958, researchers have continuously monitored animal populations there.

“It’s very quiet,” said Hoy, a research assistant professor in Michigan Technological University’s College of Forest Resources and Environmental Sciences. “It makes monitoring wildlife so much easier.”

Despite the serene environment, new research published earlier this week on wolves and moose in the special environment of Isle Royale provides fascinating insights into the relationship between predator and prey.

According to the study published in Frontiers in Ecology and Evolution, wolves are taking down moose with arthritis and killing them at an inordinate rate. Moose on Isle Royale may need wolves, according to the study, to keep their populations healthy against disease. The research could offer data for new arguments in the contentious wolf management debates that plague many communities, where some ranchers see the creatures as a threat to their livestock and livelihoods.

A researcher’s paradise

For scientists, Isle Royale has long been a fascinating research aquarium.

“It’s the longest predator-prey study in the world,” said Doug Smith, a wildlife biologist who has worked on Isle Royale in the past and now runs a wolf restoration program for the National Park. Service in Yellowstone National Park.

For more than a century, scientists have observed dramatic changes in wolf and moose populations.

Moose are thought to have arrived on the island first. A few animals likely swam (moose are unstable on ice) more than a dozen miles to the island in the early 1900s, Smith said. Their population has settled into a boom and bust pattern.

“The moose literally eats itself out of the house and the house and then it dies massively. They crash, then it all starts again,” Smith said.

Then came the wolves.

They arrived on the island around the 1940s, likely traveling over a 15-mile ice bridge that sometimes forms between Isle Royale and mainland Minnesota.

Wolves are the only predator to eat moose on the island. “By keeping wolves in Isle Royale, you control the moose population, which means they don’t eat up the entire forest,” Smith said. “Without a predator, they repeat the whole cycle.”

Diseases, tick epidemics and harsh winters have led to certain demographic trends. But in recent years, climate change has had such a big impact that the US government has decided to intervene.

Ice bridges to the island once formed seven out of 10 years. Today, those bridges only form once or twice in the same time period, Smith said.

And in recent years, the wolf population has dwindled to just two — a very inbred pair that was both father and daughter and brother and sister, according to Hoy. They could not produce puppies that would survive.

“The reason why the wolf population collapsed was clear. It was because of the loss of the ice bridge. They had no more connectivity,” Smith said. “Genetic depression.”

The moose population began to skyrocket.

The U.S. Fish and Wildlife Service started a project in the fall of 2018 to relocate wolves to the island to provide genetic diversity.

A bull moose near Pebble Creek in Yellowstone National Park in Wyoming on April 6, 2017.Jacob W. Frank / NPS

The perfect prey

Researchers visit Isle Royale at least twice per season.

“We work in the winter because it’s easier to track and observe wolves and moose. They leave tracks in the snow,” Hoy said. Aerial surveys are easier when there are no leaves on the trees.

During the summer, volunteers and researchers help collect moose remains, which provide research data points.

In the recent Frontiers study, researchers evaluated the bones of moose killed by wolves over a 32-year period, from 1975 to 2007. More than 38% of the 1,572 moose skeletons they examined showed signs of osteoarthritis.

Analysis of wolf kills suggests they preyed more frequently on older moose. Wolves did not appear to target moose in their prime, unless the moose had severe arthritis, the study found.

Arthritis rates in moose have increased over the years with lower mortality rates in wolves, the research found.

To kill a moose, a wolf must attack an animal about 10 times its size with only its teeth, so it makes sense that wolves are successful in taking down those unable to move well, Hoy said.

The study suggests that wolves could play an important role in controlling genetic diseases by eliminating diseased animals from the population. This follows similar research on deer, which shows wolves can help lessen the effects of easily spread infections like chronic wasting disease.

“It’s a good example of how the predator is actually helping the moose population,” said William Ripple, a professor and ecologist at Oregon State University, who was not involved in the research. “Wolves don’t just take prey at random. It turns out that they will take more diseased prey than by chance, and this has strong evolutionary implications for natural selection.

In other words, it’s possible that a landscape with wolves produces genetically healthier moose, although more research is needed.

Ripple said he considers the Isle Royale research to be conservative and credible.

Wolf policy

Wolves are a controversial subject.

Driven to near extinction in the mid-20th century by poisoning, trapping and shooting, the Endangered Species Act and wolf restoration projects pushed their numbers to more than 6,000, according to the Fish and Wildlife Service.

But wolves are not welcome in many ranching communities. Animals sometimes attack livestock.

When wolves arrived in Washington state, for example, they sparked decades of lawsuits, bitter political battles, and even death threats for wolves and humans alike.

In some states, poaching and poisoning cases are not uncommon, and wolves are killed by state wildlife managers after attacking livestock.

The federal protected status that has kept the species off-limits has changed with the political seasons. The Trump administration removed gray wolves from protection in most of the United States in 2020, allowing them to be hunted. This year, a federal judge overturned the Fish and Wildlife ruling in that case, restoring protection in many areas. State policies in the northern Rockies — where wolves have no protection — have recently expanded hunting.

Despite political battles, other research has suggested that wolves may have an outsized positive role on ecosystems.

Years ago, Ripple revealed that aspens began to die off in Yellowstone after the wolf massacre in the 1920s. The disappearance of wolves caused a proliferation of elk, which ate baby aspens.

Other research suggests that wolves could help reduce the coyote population and prevent car accidents by reducing the deer population.

Hoy hopes the new research will provide a reason to avoid heavy wolf hunting and get communities to consider its potential benefits.

“Think of the widespread ecological benefits that wolves provide,” Hoy said. “What kind of things could we lose if we don’t have wolves in the landscape?”

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