This is 60-second science, I'm Jason Goldman.

GABLE: "We literally get down on our hands and knees and start slowly sifting through the leaf litter, looking through bits of hair or a little chunk of bone…

Tom Gable is tracking a predator. In fact, he’s tracking a whole pack of them.

GABLE: It's very much like a crime scene investigation….

[Sounds of Voyageurs wolves]

Since 2015, the University of Minnesota conservation biologist has used GPS collars to track 30 wolves inside Voyageurs National Park.

Those collars led Gable and his team to kill sites.

And there, amid the leaf litter, were bloodied bits of fur and bone … clues about how wolves alter the ecosystems they live, and hunt, and kill in.

The long-term study is, in a way, a quest to broaden a science story that goes back 25 years.

For wildlife ecologists, the story of the reintroduction of wolves to the Greater Yellowstone Ecosystem on January 12, 1995, has become canonical.

The story goes something like this: as the elk grew to fear the wolves, they changed where and how they foraged.

That gave willows, cottonwoods, and aspens a better chance to grow near streams.

It also meant more river-side berries for foraging grizzly bears.

And it led to alterations in the flow of those streams, sending water in new directions.

Wolves outcompete coyotes for access to prey, so coyotes populations plummeted.

Which led to a rise in fox, rabbit, and ground-nesting bird numbers.

And so on.

Ecologists call this row of biological dominoes a trophic cascade.

GABLE: "Regardless of your inclination, it's hard not to be like, wow this is amazing. If that is true, it's really incredible."

New findings cast some doubt on the idea that wolves primarily regulate the Greater Yellowstone Ecosystem through fear and intimidation.

And regardless of the situation there, very little research has been conducted on this question in ecosystems that don't resemble the mountains and grasslands of Yellowstone.

Which brings us back to the boreal forests of northern Minnesota, and the ground that Tom Gable and his team have been crawling over the last few years.

During the winter, wolves work together to kill large prey like deer.

But Gable found that in warmer, ice-free months, wolves focus on smaller prey, like newborn deer fawns – and especially beavers.

And that’s where things get really interesting for the ecosystem.

GABLE: "Wolves, by preying on dispersing beavers, alter where wetlands are created.

If a young beaver gets killed after leaving home, it will never have a chance to build a new dam.

Even if it had started construction before becoming a wolf's lunch, the dam will remain unfinished and fall into disrepair.

Beavers are ecosystem engineers. When a wolf kills one, it can have a big impact.

GABLE: "Because they prevent beavers from converting a forest into a wetland. In that regard, wolves are connected to all the ecological processes that are associated with wetlands and beaver ponds."

Ecologists have long assumed the predators can influence their ecosystems in two main ways.

One is through fear and intimidation, like in the Yellowstone story. The second is through direct killing.

The Voyageurs wolves offer up a third possibility.

The park and the forests surrounding it have more than 7000 beaver ponds. Gable estimates that wolves have a direct impact each year on around 88 of them.

That’s a mere one and a quarter percent affected.

So it's hard to argue that wolves are responsible for re-shaping the ecosystem in the broadest sense.

But it's equally hard to deny that they help to maintain a diversity of habitats across the landscape.

GABLE: "But I don't really think that estimate is a key finding, so to speak. Because I think the real goal, the real point of our paper was simply to flesh out this mechanism of how wolves do this."

The study was published in the November 13 issue of the journal Science Advances.

GABLE: "This is something worth studying, and this is likely happening in a variety of ecosystems."

[Sounds of Voyageurs wolves]

—Jason G. Goldman

 (The above text is a transcript of this podcast)

[Thomas D. Gable et al. Outsized effect of predation: Wolves alter wetland creation and recolonization by killing ecosystem engineers.]