Sunday, April 19, 2009

Cry wolf

A slow, sad drama is unfolding on a remote island, in the process providing a tailor-made teaching window into population genetics and bioethics.

Isle Royale, a large, forested island on the northwest end of Lake Superior, is separated from the closest mainland by 15 miles of cold, deep water. This isolation has produced a unique and relatively simple wilderness ecosystem, which includes a pair of species – wolves and moose – tied together by a two-link food chain.

Moose arrived on Isle Royale sometime around 1900, after a long and dangerous swim from Canada or perhaps Minnesota. Wolves followed 40-50 years later, walking across on the ice of a particularly cold winter. Since then, the wolves have been the moose’s only predator, and the moose the wolves’ primary source of food. During the last 50 years, this relationship has been observed and recorded continuously by biologists with the National Park Service and Michigan Technological University. It is the longest running study of large mammal predator-prey relationships ever made, and it has provided many insights into how ecosystems develop and operate, and how they respond to environmental change. Recent work has revealed that this small but important community may be doomed.

Genetic testing has shown that the wolf packs on the island are all descended from a single female. After generations of inbreeding, the genetic diversity of the population has fallen by half, and most of the wolves are suffering from a congenital, inherited bone defect. This condition is marked by malformations and growths of the vertebrae, which interfere with spinal nerves and cause pain, muscle weakness, and paralysis. Many wolves also have extra vertebrae and early onset arthritis, which may be genetic as well. This discovery may explain recent declines in the island’s wolf population and suggests its future is likely to be both short and bleak.

Biologists and policy makers are now grappling with the difficult question of how to respond to the wolves’ predicament. Do they let nature take its course, and use the opportunity to learn more about the progress and consequences of local extinction events? Or do they attempt a “genetic intervention” and bring in one or more healthy, unrelated wolves to deepen the gene pool, which might both save the Isle Royale population and also provide valuable experience and knowledge on restoring the health of threatened species?

The story of wolves and moose on Isle Royale provides a wealth of opportunities for biology teachers. The ethical questions surrounding the wolves’ future are ripe for classroom discussions on conservation, wilderness, and the interplay between science and public policy. The data provided by 50 years of moose and wolf studies can easily be used to illustrate population dynamics, the founder effect, genetic drift, and interspecific competition. Students can be asked to use their knowledge of ecological processes to predict the environmental impact of wolf extinction on the island’s ecosystem as a whole, or to describe how even such a remote setting is influenced by regional and historical trends such as climate change and agricultural and wildlife management practices.

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