狼群如何影响森林的生态系统(下)

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. "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.

"Because they prevent beavers from converting a forest into a wetland. And 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. "But I don't really think that estimate is a key finding, so to speak.