Lake Superior is the world’s largest freshwater lake. An uninhabited island in the middle of the lake, Isle Royale, is famously home to wolves and moose. This predator-prey interaction has been the subject of a study lasting over 50 years. As the future of wolves on the island becomes uncertain should scientists intervene to save the population?
Historically the island was home to the Canadian lynx, though were hunted into oblivion by human visitors. This meant that the predator free island became fairly friendly for the herbivorous inhabitants.
Moose have not always inhabited the island and were first spotted there around the time of the First World War. How they ended up on the island is still debated. Early theories suggested that the moose either walker along an ice bridge, when the lake froze during a harsh winter, or swam the 20 miles distance between the island and the mainland. A key argument against this theory is that moose are solitary animals that don’t tend to travel in groups. For a population to emerge, this journey must have been made several times by different moose, which is highly unlikely. It is more likely that humans introduced the moose to create a hunting resort on the island. Whilst it is unlikely the moose made the journey across the lake, it is the most likely scenario for wolf colonisation.
Scientists studied the predator-prey interaction between wolves and moose almost immediately after the first wolves arrived and have continued ever since. The island was a near perfect home for such a study, with moose making up almost 90% of a wolf’s diet, and wolves being the only predator for moose on the island. Changes to the population sizes could be measured regularly, and the effects of population growth in one species could be recorded in the other.
Population sizes of both species fluctuated for decades, with the wolf population increasing when there were more moose, and then declining as their source of prey decreased. For a while, the populations seemed to reach equilibrium, with around 20 wolves and 1000 moose. However, the isolation from the outside world that benefited the scientific studies lead to the downfall of the experiment.
The problem with closed populations is that they are closed – a small population of wolves will inevitably inbreed. The gene pool became narrower, with the chances of new healthy & fertile offspring reducing. For years, this problem was alleviated by the occasional emigrating wolf crossing an ice bridge. This provided new genes into the gene pool, keeping the wolf population healthy.
However, with the climate changing, ice bridges rarely form. Today, the island’s wolves remain completely cut off from the wolves living 20 miles away on the mainland. Only two wolves, a male and female, remain on the island – although new offspring are unlikely. The female is the male’s daughter, but also his sister because she was a product of reproduction with his mum. This complicated relationship means that the two remaining wolves share 75% of the same chromosomes.
Scientists are undecided as how to resolve this situation. Some argue that as the population isn’t historically from the island we should let them die out. There are also arguments to maintain the wolf population. Scientists would like to continue their population studies, and the local authorities wouldn’t like the inevitable moose population expansion if their only predator was to disappear.
Public consultation on the matter is ongoing, with a final decision being made later this month. The most likely scenario is that new wolves are added to the island in a genetic rescue operation. This would allow for the continuation of scientific studies, with the genetic rescue representing the effect of the occasional ice-bridge-emigrating wolf.
What do you think should happen? Is the genetic rescue a good idea? Leave your thoughts in the comment section below
To read more about the Isle Royale wolves, I suggest you like the Isle Royale Wolf and Moose Project Facebook page