Tuesday, April 2, 2013

Wolves Teach Scientists Their Limitations

April 1, 2013
The "West-End Trio," one of two wolf packs remaining on Isle Royale.
The “West-End Trio,” one of two wolf packs remaining on Isle Royale.
The gray wolves of Michigan’s Isle Royale may soon go extinct. But before they do, they’re offering an important lesson for scientists: Have a little humility.

For more than 60 years, after their intrepid ancestors scrambled 14 miles across an ice bridge, packs of heavily inbred wolves have stalked the snow and evergreens of Isle Royale, a remote 850-square-mile archipelago in northwestern Lake Superior. For all that time, the wolves, normally known for their catholic prey selection, have feasted and famished off a single species, the yin to their predatory yang. They have hunted moose.

We know this because for as long as the wolves have stalked the moose, they have been tracked by a pack of Michigan scientists, in what has become a classic, 55-year-old study of the dynamics between a predator and its prey. In an age when much research lasts no longer than a graduate student’s labors, the study is an anomaly. Forget Big Data. This is Long Data.

You might think that 50-plus years of tracking what amounts to a simplified natural system—given the archipelago’s isolation, the wolves and moose on its large main island face little competition—would paint a clear picture of the boom-and-bust cycles expected from predators and prey. But that’s hardly the case, says John A. Vucetich, an associate professor at Michigan Technological University and the study’s leader.

For ecology, the project’s biggest lesson has been “our inability to make predictions about what’s going to happen next on Isle Royale,” Vucetich says. He should know: He’s been on the project since he was 18 years old, when he joined as a technician. For the project’s staff, and the broader world of ecology, “it’s been one long education,” Vucetich says.

For the study’s first two decades, it seemed the moose’s numbers were controlled by the newly arrived wolves, as classical predator-prey theory might suggest. (The moose themselves are island arrivistes, having appeared in the early 20th century. They could have swum, or maybe human beings brought them; no one knows.) “If I had studied it for 20 years, I would have thought I had the place figured out,” Vucetich says.

But then, for the next 20 years, it all changed, with climate seeming to dominate the moose’s survival.
Today, the scientists are less certain of climate’s importance. Isle Royale sits at the southern end of the moose’s natural range, and so you might expect their numbers to dwindle in the face of global warming. Not far away, the moose population in northeastern Minnesota has plummeted by two-thirds over the past three years, a change many chalk up to climate change. But over roughly that same period, the Isle Royale moose have increased by 80 percent, to nearly 1,000 strong, Vucetich says.

“There’s an awful lot of calves on the island,” he says.

Part of that moose surge is bound to be wrapped up in the fate of the island’s wolves, who are nearing local extinction. Eight wolves are left—down from a long-term average of 24—and over the winter, researchers saw no evidence of new pups, a finding published last week.

That’s surprising because mating is about the easiest thing wolves can do. Their day-to-day work of survival—wolf hunts fail more often than you might expect—is far more draining. Since a wolf’s life on Isle Royale is inbred, brutish, and short, a few pup-less years would doom the remaining population.

Certainly genetic depression is one reason for their decline. Like people, wolves are reluctant to reproduce with their own kin, and all the island’s wolves descend from one 1950s female. Until a few years ago, scientists thought the pack was a rare example of an inbred group that had suffered no negative consequences. The researchers were wrong, they recently discovered. The wolves’ genes are too few, and too similar; the inbreeding depression found in the wolves can cause painful spine malformations in domestic dogs.

A few fates are possible for Isle Royale. The National Park Service, which controls the archipelago, could allow the wolves to go extinct, leaving it for the moose. (The park has existed since 1940, with much of it designated wilderness in 1976.) The Park Service could attempt a “genetic rescue” of the wolves, introducing new wolves to improve their sorry gene pool. Or it could allow the extinction, and then move more wolves to the archipelago in a few years.

What the government decides to do is likely to reflect a shift in the values of society and conservation. Back in the 1980s, Isle Royale’s wolves suffered from an outbreak of canine parvovirus, accidentally introduced by people. The service debated what to do then, as it wrangled with fears about interfering in a pristine wilderness. But given global warming, it’s hard today to see any wilderness as pristine. So the Park Service will have to decide what exactly it wants from Isle Royale. Those discussions continue; in the 1980s they went on so long that the wolves rebounded in numbers before a solution appeared.

Vucetich is agnostic on what happens to Isle Royale, beyond preserving the presence of wolves (and his research). But if genetic rescue is attempted, his project can teach another lesson: In 1997 a lone male wolf made it to the island, and he became very popular indeed. Within a decade, two-thirds of the wolves’ genes traced back to him.

His fitness had a flip side, though. The lone wolf’s genes quickly became a new source of inbreeding. “His positive effect was powerful but very short-lived,” says Michael P. Nelson, an environmental philosopher at Oregon State University and longtime collaborator with the Isle Royale study.

A shorter-term view would have missed that genetic wave and its decline, he adds. “When you watch something for a very long time, sometimes the simplest observation can have a great deal of meaning,” Nelson says, “and it’s only because of that context.”

Vucetich will return to the island in a month, searching for more evidence of pups. His budget is modest but seems stable, though he’s wary of the effect of budget cuts stemming from the federal government’s sequestration. But whatever happens to the wolves, or his budget, it’s likely he will still be there on Isle Royale, beneath the white spruce and paper birch, watching, tracking.

[Image by J. Vucetich, Wolves & Moose of Isle Royale.]