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Expanding forests darken the outlook for butterflies, study shows

July 19, 2005

Changing environmental conditions in the Canadian Rockies are stifling the mating choices of butterflies in the region, say University of Alberta researchers.

Smaller and less abundant alpine meadows-largely the result of human activities-are diminishing the alpine butterfly gene pool, creating a pattern that could lead to the butterflies being less able to survive, said Dr. Jens Roland, a biological scientist at the University of Alberta and an author of a paper on the subject that has been published recently in Molecular Ecology.

Working with colleagues in the U of A Department of Biological Sciences, Roland and doctoral student Nusha Keyghobadi used samples of butterfly dispersal and genetic variability taken from the Kananaskis region in Alberta to show a correlation between less genetic diversity and smaller meadows.

According to Roland, the altitude of the tree line in the Canadian Rockies is rising-likely due to global warming-and, outside of national parks, forest fires are usually suppressed. These factors are combining to create larger forests and smaller alpine meadows. This is bad news for butterflies in the Rockies, such as the Parnasissus, which Roland studies, because they require two things that they can easily find in meadows: sunlight and stone crop.

Butterflies need sunlight to elevate their body temperatures in order to fly, and forests are generally too shady for them to travel through with quickness and ease. Parnasissus also need stone crop, a plant that grows in meadows and is the only suitable host for alpine butterfly larvae.

Therefore, alpine butterflies do not generally travel beyond the meadows they are born in, and the shrinking meadows could lead to inbreeding and the decreased diversity in the gene pool, Roland said.

"In general, inbreeding leads a species to be more vulnerable to a variety of mortality factors that lower survival rates," Roland explained. "This has been demonstrated for other species of butterflies."

Only a few species of butterflies are threatened in the Canadian Rockies, but many more are threatened in Europe, where the problem of shrinking alpine meadows is older and more acute. Roland believes the results of his study can inform conservation biologists in Europe to help them save their butterflies.

As for protecting the butterflies in the Canadian Rockies, Roland would like to see more prescribed burning of forests to increase the number and size of alpine meadows. However, unlike the park areas, the unprotected land areas are often used for commercial purposes and are therefore less likely to be allowed to burn.

"They do prescribed burning in the national parks for general maintenance, but they also do it to increase the meadow areas, which animals such as sheep and elk like to inhabit. The offshoot is that it also helps smaller animals, such as the butterflies," Roland said.

University of Alberta