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Posts Tagged ‘Isle Royale wolves’

isle royale wolves

One of the classic studies in wildlife management happened on island in Lake Superior. Isle Royale, part of the state of Michigan but much closer to the state of Minnesota and Northwest Ontario, is home to a population of moose. These moose either swam across from Minnesota or were stocked there in the early 1900, and they found themselves in a paradise. No predators existed on the island, and the island was full of birch trees and aspen colonies.

Over time, the moose denuded the aspens and the birches, and they were forced to eat balsam fir. In 1949, when Lake Superior was frozen over, a pair of wolves crossed to Isle Royale, and they were the foundation for a wolf population that specialized in hunting moose.

This island became of interest to ecologists early on.  It had been made a national park in 1940, and as a national park, it has no permanent residents. Because wolves and moose live on the island without any chance of humans hunting them,  early predator-prey researchers went to the island to see if Paul Errington was right.

Paul Errington was professor of zoology at Iowa State University. He had studied bobwhite quail population dynamics while a student at the University of Wisconsin, during which time he became close friends with Aldo Leopold. Leopold was not faculty member, but Errington learned so much from him during his time at the university. Errington was

Errington’s most famous research was performed in the marshes of Iowa. There, he studied the population dynamics of muskrats and American mink. Muskrats, which are giant water voles, are a major prey source for the mink, and one would think that mink would severely reduce muskrat population. However, Errington’s research found that mink predation had no real depressive influence on muskrat numbers.  He found that the mink tended to take young and infirm. Most healthy muskrats  were generally left alone.

This research, which was published in 1943, was the hottest idea in the nascent science of ecology, and researchers were looking for places where this hypothesis could be tested on a grander scale.  Isle Royale fit the bill, and the first studies of wolf and moose dynamics on the island started in 1958.

Initially, the research found similar findings to Errington’s muskrat and mink study.  Moose and wolf populations fluctuated over the years. When the moose became too numerous, they were forced to eat more and more balsam fir. The fir is not nutritious, and the moose gradually become emaciated. Because the moose require lots of nutrition from their bones to grow their antlers, they also wind up suffering from arthritis.  Emaciated, arthritic moose are easy prey for wolves, and wolf numbers increased when the moose hit this stage.  The wolf population would then increase, and after a few years, it would begin to pare back the moose population to allow birches and aspen to recover.

But at the same time, there weren’t enough weak moose for the wolves to hunt, and the wolf population would crash. The moose would find themselves in a situation with more limited predation and better forage, and their numbers would increase again. And the cycle would start again

When I think of Isle Royale’s wolf and moose dynamics, I think of the work of Rolf Peterson, who made a career out of studying the wolf and moose population fluctuations.  He began to notice that the balsam firs on the island were not regenerating through each moose and wolf fluctuation.

These findings meant that Isle Royale would not be able to continue on through constant moose and wolf fluctuations as one might have hoped, and this problem became worse when the wolf population really crashed.

Lots of debate exists about how well wolves can withstand inbreeding. Climate change has meant that ice bridges that connect the island to Minnesota and Ontario no longer form, and those that do form aren’t around very long. So the wolves have been inbreeding on the island for decades. They were able to withstand this inbreeding for decades, but in the 1990s, the population really began to suffer from this inbreeding depression.

In 1997, a lone male wolf, “Old Gray Guy,” wandered onto the island, there was hope that his genes would be a genetic rescue on the island.  He apparently did introduce some much needed genetic diversity to the island, because by the 2010s, 56 percent of all wolf genes on the island could be traced to him. Wolf fertility did not increase as the result of his arrival, and although a debate exists as to whether there was anything like a genetic rescue on the island, it should be noted that Old Gray Guy was very much like a popular sire in a purebred dog. The population was already quite inbred, and the influx of only a single male that winds up contributing that many genes to the population isn’t going to save the population

By the first decade of this century, a genetic disorder of the wolves’ spines became rampant in the population.  The wolves began to die at early ages, simply because they were unable to walk or because movement was painful for them.

At that time, a real debate existed about bringing in wolves from the mainland, but caution was exercised. There was a hope that natural selection would purge the spinal deformities, but this purge never came. When the ice bridge formed during a polar vortex collapse in 2014, there was also real hope that wolves would walk over to the island. However, all that happened was that two Isle Royale wolves left the island, and one was found dead on the Minnesota mainland.

Further, because the purpose of the studies on wolves and moose on Isle Royale was to see what predator and prey relations are like without the use of human intervention, there was very real resistance to introducing more mainland wolves.

However by December 2017, only one wolf was thought to be living on the island, and the moose population exploded.   However, the moose themselves were physically smaller and would very likely eat themselves out of forage in short order.

This past September, a plan was hatched to restore the wolf population to Isle Royale.  Wolves from the UP of Michigan and northeastern Minnesota would be released upon the island.  Yes, after decades of allowing nature to take its course, man would finally intervene in these predator-prey dynamics.

Things are not off to a good start, however.  One of the first three wolves released on the island has already used the formation of an ice bridge in the most recent polar vortex collapse to escape back to the Minnesota mainland.

However, wildlife managers aren’t giving up. Currently, there are plans to release six wolves from Ontario’s Michipicoten Island onto Isle Royale.  These wolves, which also live on an island in Lake Superior, have a bit of a storied reputation.

On their island, there was once a thriving population of woodland caribou, but the wolves have reduced their number from over 900 to just 30 individuals.  The  caribou were not native to the island, however.  A bull just happened to pop up on the island, and other woodland caribou were stocked to create a population, which thrived until the winter of 2014-2015.

That is when wolves walked across an ice bridge n Michipicoten, and they found it a paradise for wolves. Finding a vast horde of ungulates was a boon for their numbers, but by it took them just a few years to drop the caribou numbers. The caribou are now being taken off the island, but the wolves have had virtually no options. the wolves have had virtually no options.

These Michipicoten wolves are large-bodied creatures that definitely have the ability to hunt large ungulates, so there are very real hopes that these wolves will be able to reduce Isle Royale’s moose population.  New studies on their population dynamics can begin, and this experiment continues on.

That is the hope, anyway.  Whatever happens in the next few months, it should be noted that Isle Royale and the related Michipicoten experiences is that both are studies in a really controlled environments that no longer exist in North America, if they ever did at all.

Moose, caribou, and wolves are all at the mercy of a human-dominated world.  These islands give us an idea of what the world would be like if predator and prey dynamics were left alone, but they aren’t necessarily indicative of how these dynamics would exist on a continent in which human interests have great knock-off effects upon ecology.

After all, the Isle Royale moose and wolves are not directly affected by human hunting. They are still controlled by climate change.  Warmer than normal winters mean that the ice bridges don’t form, and the collapse of the polar vortex, which is also caused by climate change, means that the inbred wolves just don’t want to stay on the island. Moose are getting weaker and weaker as the ticks spread through the populations, and without long periods of cold, the ticks are able to infest the moose, weakening them in greater numbers every year.

The Isle Royale studies are the studies of an island where hunting isn’t allowed, but virtually every place where wolves and ungulates exist on this continent, hunting is a major point of human interest. Humans want more ungulates on the ground, and if their numbers ever drop, wolves will be blamed.  Wolves certainly can have an effect upon prey numbers, and even more than that, they have an effect upon prey behavior. Trophy cervids are just harder to kill if they spend much of the year being harried and herded by wolves.

Maybe what we can know from Isle Royale is limited, but in those limitations, we might get an idea of how to mitigate all these competing interests and have some way of keeping large predators as part of our North American wildlife heritage.

If wolves are not restored to Isle Royale, the landscape will likely be denuded of trees, and all that will be left is a population of tick-invested, diminutive moose.  They will always be on the edge of famine.

Restoring wolves gives a potential hope, but nothing is guaranteed.

But the saga goes on. Maybe for just a bit longer, or maybe new, bright future exists for this most storied of predator and prey studies.

 

 

 

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The real lessons learned from the inbred population of wolves at Isle Royale, Michigan.

 

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Old Gray Guy is the large light gray wolf in the middle of this pack.

From NY Times:

In Ontario, in the winter of 1997, a particularly virile male wolf stepped onto the ice of Lake Superior and headed toward Isle Royale, an island about 15 miles offshore. There he radically changed the genetic makeup of an isolated group of wolves that had lived there since the late 1940s.

Researchers, who for many years have been observing the Isle Royale packs and the moose they feed on, did not realize at first that he was an immigrant, but soon his appearance and behavior became impossible to ignore.

He was larger than most of the Isle Royale wolves, and was so strongly territorial that he completely displaced one of the four packs, driving it to extinction within two years of his arrival. His own pack grew to 10 wolves, the largest seen on the island in almost 20 years. As he aged, his fur grew paler, almost white, a phenomenon known in other wolves but never before seen in the Isle Royale animals.

“We don’t know of any other instance — except when they first came — of wolves crossing the ice,” said John A. Vucetich, the lead author of a study of the wolves published online in The Proceedings of the Royal Society B last week. “The entire population is descended from a single female.”

The wolf population on Isle Royale is small under any circumstances — there were only 16 wolves there last winter, and the average is about 23. But by 2002, the new wolf, now designated wolf No. 93, and his offspring made up five of the six breeders. In his eight years of breeding, he produced 34 pups, and those pups produced an additional 45 progeny.

By analyzing DNA found in blood from some captured animals and in scat from many more, the researchers were able to determine that by 2009, 56 percent of the genes in Isle Royale wolves could be traced to wolf No. 93, or the Old Gray Guy, as he became known.

Such a change is clear evidence for a large difference in fitness between the Old Gray Guy and the other wolves, and scientists expected that the introduction of such a an animal into a small inbred group would produce a sharp increase in population — what scientists call a genetic rescue.

But in this case, it did not happen. A co-author of the study, Rolf O. Peterson, a research professor at Michigan Technological University, said that the population of Isle Royale hangs on by a thread, as it has for decades. The average reproduction after the Old Gray Guy arrived was no different from before. Yet this does not mean that he had no effect.

“The simple interpretation is that genetic rescue doesn’t work,” said Dr. Vucetich, an assistant professor of wildlife ecology at Michigan Technological University. “But what happened here is that when the immigrant came in 1997, in the decade that followed, the moose population declined radically. It’s plausible that we didn’t see an effect because the wolves were suffering from some other trouble that disguised the benefit.”

That, said Dr. Vucetich, is “an important lesson all over the world. When you do genetic rescues and it looks like it didn’t work, there may be a beneficial effect that you don’t see because of some other environmental event.”

What if wolf No. 93 had never arrived? Dr. Vucetich said that it is impossible to know for sure, but the Isle Royale wolves might have disappeared completely. It may be that the Old Gray Guy arrived just in time.

(Jess sent me an earlier article on Old Gray Guy from Science Daily, but I thought the Times had a better write-up on it.)

The authors of that study talk about the ecological factors that could have prevented the genetic rescue from happening.  Those factors would indeed mask any benefit from outcrossing.

But there are other factors.

This is a very small, very inbred population of wolves. It was suffering the effects of an inbreeding depression. An outbred wolf from Ontario shows up. When he mates with a local female, more of his puppies survive than the native inbred population. He winds up siring a large percentage of the a few generations of the wolves on the island, and because those are also quite outbred, they have better ability to swamp the gene pool. They are just better at surviving to pass on their genes than the pups born to the inbred population. This effect would be even more extreme if the prey population happened to be in decline. The outbred wolves may have had certain advantages from heterosis that kept them from succumbing to the stresses of famine.

He becomes like a popular sire within a closed registry breed– in fact, even more extreme.

Whatever benefits could have come from outcrossing are lost in this extreme natural version of the popular sire effect.

If more than one wolf had come across from Ontario and contributed genes to the Isle Royale wolf population, one might be able to make generalizable statements about genetic rescue. And maybe if several wolves had arrived at the same time as a moose population boom, things might have been different.

If Old Gray Guy hadn’t arrived, these wolves may have gone extinct already. His genes may have not have rescued them fully, but it is likely they ameliorated some of the worst effects of the inbreeding depression, preventing the population from collapsing entirely.

Isle Royale is an unusual place, but because of its size and isolation, it is a good place for scientists to design experiments about ecology and population genetics.

However, because it is so unusual, one cannot make such broad generalizations about the findings of many studies performed on the island.

We have seen genetic rescue save the Florida panther. Eight Texas cougar queens were released in South Florida in 1995.  Five of the queens had litters and then were sterilized.  The health and genetic diversity of Florida panther is now much better than it was before. The population has risen from about 24 to nearly 100 individuals. The population still remains isolated, and there can still be threats of an inbreeding depression in the future. No new genes are likely to come into Florida any time soon.

But genetic rescue works in certain situations.

But it won’t work with just one male individual entering the population when the population of the prey species is in decline.

Genetic rescue requires more individuals and relatively productive ecosystems to work.

That’s likely why it worked with the Florida panther and not with the wolves of Isle Royale.

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