Back in 2012, I noted that the wolves on Isle Royale in Lake Michigan were on thin ice due to inbreeding. At that point, there were just 9 wolves left.
In 2017, I noted that just two aged wolves (father and daughter) were left on the island. Would the National Park Service let the wolves die out, or import new ones?
It seems the decision has been made, and two new wolves from Minnesota have been released on the island.
Without a doubt some lessons will be learned. Hopefully some already have been.
I described the Isle Royale situation back in 2011 in a post entitled Islands of Wolves, Rats, Lions and Dogs, noting that the breeding habits, litter size, and lifespan of species matter a great deal when it comes to genetic bottlenecks.
Now imagine that a pregnant wolf lands on an island that is 200 square miles in size. The wolf whelps five pups, and the pups interbreed and the population grows for a time until it hits some sort of food-availability threshold.
A boreal island that is 200 square miles in size and with a sizable moose population can, for a while, feed a population of 50 wolves, but eventually that population can be expected to collapse down to as few as dozen individuals before it rises again and falls again due to the vagaries of disease and weather which will impact prey species such as moose, deer and rabbit. After 75 years, the population of wolves on this island will be very inbred, and infecundity and disease will be common. The reason for this is simple: wolves typically live between six or seven years in the wild, and the smaller number of wolves on the island, combined with the smaller number of generations, means that there will be very little room for genetic drift or mutation.
Is is possible to import a single individual wolf to achieve a "genetic rescue" of this heavily inbred wolf population? A single wolf, sadly, is not likely to do it. The reason for this is simple: the small number of wolves on the island (a population of 24, on average) and their high rate of infecundity due to inbreeding, means that the genes of the new male wolf will quickly dominate. Inbreeding will then continue as before. Though there may be a short temporal improvement in population health, that may not be observed if there is a counter-balancing downtick in food sources occurring at the same time.
To be clear, this scenario is not one I have made up; it appears this is exactly what happened with the wolves on Isle Royale, Michigan.
So what will happen with two new wolves on the island?
Look for more wolves in the spring, and a small down-tick in the moose population. It will take at least 5 years before the wolves shoulder up the numbers that used to live on the island, and it will likely take another 20 years before inbreeding (assuming no more genetic introductions) starts to cut into fecundity once again. But will it? Absolutely.
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