Wolves, Ticks, Send Michigan Moose Numbers Plummeting

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Since the arrival of wolves, the fates of the wolves and moose have been intimately linked. The wolves' arrival set the stage for a natural, long-term study of a single-prey, single-predator system.

In 1958, about a decade after the first wolves arrived, Durwood Allen with Purdue University in West Lafayette, Indiana, launched the study. Peterson took over as project leader in 1975. Vucetich joined Peterson in 1990 and in 2001 was named a co-director.

In the 47-year history of the study, the researchers have observed the interactions between the wolves and moose and noted how their seesawing populations affect the entire island ecosystem.

"If you watch for a long time, you can see patterns, and patterns are what we see and what we make inferences about," Vucetich said.

Healthy Forest

A correlation between an abundant wolf population and vigorous forest growth is one pattern to emerge in the decades of data, according to Vucetich. Trees are the primary food sources for the moose, so when the moose population is high, tree growth is stunted. Conversely, when the moose numbers are low, the trees grow better.

"One idea that has been popular [in conservation biology] is the notion that predators are an important part of the health of the ecosystem," Vucetich said. "The work we've done here points to that."

Indeed, Vucetich said, this year's tree growth is noticeably greater than in recent years. Of course, he added, one good year for the moose and they can wipe out many years of tree growth.

"You can actually see the ebb and flow of the wolf population by counting tree rings and measuring the ring width," Peterson said in an interview with the radio program Pulse of the Planet.

Ticks and Weather

While the moose and wolf populations help keep each other in check, they both grapple with additional challenges such as disease (a virus nearly wiped out the wolves between 1980 and 1982, Vucetich said), a changing climate, and periodic moose tick infestations.

The researchers have only a fuzzy idea as to what spurred the current tick infestation, but suspect it is linked to a series of mild springs.

The ticks latch onto the moose during the winter. Female ticks drop off in the spring to lay eggs. If they land on dry ground, all goes well. But "if spring comes late and there's snow on the ground, they're dead," Vucetich said. In recent winters, spring has arrived early enough to allow the ticks to thrive.

Interestingly, Vucetich added, heartworm, a disease that affects dogs and wolves, recently showed up for the first time in the mainland city od Thunder Bay, Ontario, Canada, about 14 miles (23 kilometers) from the island.

The parasite, which is transferred from mosquitoes to dogs, is usually restricted to warmer southern latitudes but has been creeping north in recent years. The disease has been found in Minnesota wolves. "For it to come [to Isle Royale] many things would have to happen just so, but it gives us pause," Vucetich said.

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