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As climate warms, species may need to migrate or perish

By Carl Zimmer - posted Wednesday, 6 May 2009

With global warming pushing some animals and plants to the brink of extinction, conservation biologists are now saying that the only way to save some species may be to move them.

In the gentle hills outside York, England, a controversial experiment is quietly unfolding. It began in the summer of 2000 when Steven Willis, a biologist at the University of Durham, and his colleagues drove to a wildlife preserve called Wingate Quarry. In the back of their car was a cage full of butterflies called Marbled Whites. Willis and his colleagues removed the cage from the car, opened it, and let 500 butterflies flutter away across the scrubby meadows.

Marbled Whites are common in Europe and southern England, but in 2000 the northern edge of their range was 65 kilometres south of Wingate Quarry. Yet Willis and his colleagues suspected that they might do well there. Thanks to global warming, Wingate Quarry might now be mild enough for the butterflies to survive.


Since releasing the butterflies, Willis and his students have returned to Wingate Quarry each year. They have walked a transect, counting the Marbled Whites they saw along the way, and have searched the area around the release to see how far they had dispersed. In February, they finally announced the results of their surveys in the journal Conservation Letters. The population of Marbled Whites of Wingate Quarry is steadily growing and slowly increasing its range. “They’re certainly holding their own,” says Willis.

Willis and his colleagues did not move the butterflies purely out of scientific curiosity. A number of studies indicate that global warming will rob many species of their current habitat, pushing them towards extinction. Some conservation biologists argue that the only way to save some species may be to move them to new ranges that they can’t get to themselves.

This strategy - which goes by various names including assisted migration, assisted colonisation, and, most recently, managed relocation - only emerged in the scientific literature in 2007. Over the past two years it has attracted widespread interest. A number of scientists are now investigating how they can pick new homes for endangered species and move them safely. Willis’s new paper now provides the first proof of principle that conservation biologists can select new places where species will thrive. Congress may even include funding for research on managed relocation in upcoming climate change legislation.

But managed relocation is also now the subject of a fierce backlash from some leading conservation biologists. In a newly published essay, Daniel Simberloff of the University of Kentucky and Anthony Ricciardi of McGill University call it a game of “ecological roulette”.

By the 1990s it became clear that a number of animal and plant species were on the move because of rising global temperatures. Species in the northern hemisphere were expanding their ranges north; Southern Hemisphere species were moving the other way. Animals and plants that lived on mountainsides were spreading up the slopes. The weight of the evidence pointed towards global warming as the cause of these shifts. A warmer climate opened up new territory that some species could colonise.

While global warming might make new territories suitable for some species, it might also put other territories off limits. The hamster-like American pika, for example, lives on mountainsides and ridges in the western United States. Pikas typically lived at an elevation of 5,700 feet, but in recent decades they’ve moved uphill more than an additional 2,000 feet. There’s only so much further the Pikas can go before they run out of mountain. As a result, the Center for Biological Diversity is petitioning the US Fish and Wildlife to designate the pika as an endangered species due to climate change.


Animals that live in low-lying forests may have an easier time finding a suitable climate, but they may be hobbled for different reasons. The Quino checkerspot butterfly, for example, is an endangered species that lives in southern California and Baja. It appears to have lost some of its southern range to climate change, but it can’t shift north because it can’t survive in the urbanised landscape of San Diego.

“If you are going to migrate from southern California to northern California, you’ve got to get past Los Angeles, and then you’ve got to get past San Francisco,” says Dov Sax of Brown University. “If you can’t, you’re done for.”

Even if species have clear pathways, they may not have enough time to keep up with the speed of climate change. As they creep towards suitable climates, the warmer end of their range may become uninhabitable. As a result, they will become trapped in smaller areas. In 2001, Willis was one of 15 researchers who surveyed 46 species of butterflies in Great Britain and found that three-quarters of them had declined over the previous 30 years - a result consistent with a loss of range due to a warming climate.

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First published in Yale Environment 360 on April 20, 2009.

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About the Author

Carl Zimmer writes about science for The New York Times and a number of magazines. A 2007 winner of the National Academies of Science Communication Award, Zimmer is the author of six books, including Microcosm: E. coli and the New Science of Life. He also writes an award-winning blog about science called The Loom.

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