As I have been reading through the Isle Royal Annual Reports, I was wondering if the genetic loss which resulted from the high inbreeding levels and lack of immigration (a consequence of increasing isolation of Isle Royal from mainland as an effect of warmer winters and lack of ice cover on Lake Superior) could have been exacerbated by the relatively simple system where the wolves preyed mainly on moose and, to a lesser extent, beaver.
While there were also snowshoe hares found in wolf scats and squirrels, deer mice, possibly some bird species were available, these prey resources are normally utilized during times of low main prey abundance.
The wolves on Isle Royale, as far as I understand, did not suffer extremely low moose abundance and thus they would not have been ‘naturally encouraged’ to switch to alternative prey.
While such situation is not abnormal, in a highly inbred population, it would have resulted in ever lower selectivity for diverse genes (that demand for dietary flexibility and multiple foraging skills).
Additionally, the wolves did not roam over vast ranges and they were probably rather familiar with the area which was not comprised of a great range of diverse habitats (especially, with respect to larger packs that tended to settle either in the west or the east of the island where the major habitat was rather homogeneous).
Thus, from the environmental perspective, these wolves would not have been selected for genes that allow functional and adaptive diversity.
Genetic richness would be mainly achieved not by adaptation to local environment but rather by outbreeding which became increasingly rare.
I wonder if the ecotype-genotype interaction (both with a tendency toward impoverishment) might have resulted in a faster and more irreversible decline of genetic diversity in the population.
It would be interesting to study whether complex prey-predator interactions in a particular region (including a variety of habitats on the wolves’ range and perhaps also a variety of other predators and scavengers, i.e., competitors) would contribute to retention of higher genetic diversity (at different immigration levels).
It might be important to bear in mind, that in our times, the species composition affecting the adaptations by wolves to their local environment (prey assemblage, competitor assemblage) has been impoverished in many world regions where only a fraction of, for example, prey historically available to wolves has persisted (e.g., loss of bison, loss of moose in some areas or elk in other areas, reduction of the range of red deer or roe deer etc.) and the predator/scavenger guild is also reduced.
What if this has led to a greater necessity to maintain genetic diversity through immigration/emigration processes?
Many world regions worry over the estimates of wolf effective population size that is necessary to maintain genetic diversity and often it appears almost impossible to achieve such population size (e.g., 500 breeding adults in Europe leading to at least 1000 packs in order to ensure genetic exchange and a constant supply of available mates from other areas and from other subpopulations).
Perhaps earlier genetic diversity was partly maintained due to environmental heterogeneity and species richness leading to a greater persistence of local populations even where gene exchange would be slow (e.g., in long-term stable populations).
Another tool to achieve genetic adequacy in wolf subpopulations might be to restore species assemblages and to diversify the landscape.
Notes by Ieva 