Friday, March 16, 2012

Isle Royale Wolves on Thin Ice

In an earlier post entitled Islands of Wolves, Rats, Lions and Dogs, I detailed the different social-demographic-and genetic loads and problems that occur when different species occupy islands or otherwise suffer from extremely isolated (and therefore inbred) populations. 

As I noted, what species an animal is, where it feeds on the pyramid, and how it lives and loves are very important issues so far as genetic health and long-term population viability are concerned.

To illuminate that point I compared the extreme genetic isolation of the Isle Royale Wolves in Michigan to what has occurred when rats, and lions have found themselves on similar sized islands.

Now comes word that scientists are worried that the Isle Royale Wolves may go extinct

Isle Royale National Park's gray wolves, one of the world's most closely monitored predator populations, are at their lowest ebb in more than a half-century and could die out within a few years, scientists said Friday.

Only nine wolves still wander the wilderness island chain in western Lake Superior and just one is known to be a female, raising doubts they'll bounce back from a recent free-fall unless people lend a hand... There were 24 wolves — roughly their long-term average number — as recently as 2009.... The only intact pack had six members. One wolf wandered alone, while a couple — including the only known female — staked out territory and apparently mated.

Should the Isle Royale Wolves be allowed to go extinct?

If that happens, what will happen to the moose population, and what will that mean for the island's vegetation?

To be clear here, there is no great decision to be made here. 

We have many thousands of wild wolves all over the lower-48 now, and extremely healthy wolf populations  exist all over Canada and Alaska as well.  The wolf is an animal that is not only off the Endangered Species List, but is allowed to be hunted in a few states. 

The fate of a dozen wolves on Isle Royale, then is largely a philosophical debate, and not necessarily one of great import or permanence.  After all, wolves did not exist on Isle Royale at all just 70 years ago.  Even if all the wolves on the island died out this year (a very unlikely scenario), a hard freeze over Lake Superior next winter might return a new population from the mainland soon enough.


Jennifer said...

You use the r vs k strategy argument to explain how some founder populations survive despite narrow gene pool . . . but to say dog breeds are in trouble. I don't disagree that some dog breeds are in trouble, but I don't think you have the island biogeography / ecology right.
Russel et al's (2009) rat study did not conclude that mutation and genetic drift were saving the rats. To the contrary, they hint that the population may be declining and suggest it's unfortunate that inbreeding depression happens too late to save island ecology from being stripped by rats.
If k strategists were more vulnerable, you'd think the Isle Royale moose, which twins only when food is abundant and has a 230 day gestation, would be in much worse shape than the wolves.
You must also consider alternative hypotheses, eg., by chance the founder population of wolves carried some genetic defects, which were amplified through the parvo bottleneck of 1980. Note, the fox populations in the Channel Islands seem to be doing ok, genetically, despite long term isolation and a parvo bottleneck.

PBurns said...

Jennifer, moose can easily swim miles and miles. They do it all the time, crossing enormous lakes on their own. Wolves, on the other hand, will not cross even a small pond.

Rat populations suffer fertility depression due in inbreeding, but the depression is not enough to offset their numbers. A 20 percent decline in wolf fertility, when there are only 12 wolves, is a killer. A 20% decline in rat fertility when there are 500 rats a barely a tap on the brakes.

The idea that there is "good" genetic stock and "bad" genetic stock is true but overstated. EVERY animal carries bad recessive genes within, and bad recessive genes are also created through mutation (as are good). The result is that if there is a very small population (start with 2)that breeds slowly, but in which inbeeding occurs, very bad things turn up after 30-50 years or so; this is why Zoos are very careful to rotate their stock and track lines to avoid inbreeding.

Fox do not pack and breed like wolves, but more like rabbits, with short lives. All adult males and females are likely to have offspring, unlike with wolves.

The term "bottle neck" is over-used. Unless the number of Channel fox dropped to less than 20 and those animals were also very closely and recently related (they would not be), things will tend to work out over time. I recently saw the term "bottle neck" used to refer to a population of 15,000 individuals scattered all over the world. Ridiculous!

PBurns said...

You mention someone by the name of Russel on rat populations. I have no idea who this is, but if it is James Russell, I would point you to this link >> and especially the last line of the paper where he notes: "Norway rats appear to be capable of establishing populations, such as on Moturemu, despite founding
populations of only a small number of individuals, and increased rates of inbreeding. This apparent lack of shortterm genetic consequences on immediate establishment should explain in part why Norway rats have successfully colonised so many islands."