Can "Assisted Migration" Save Species from Global Warming?

As the world warms up, some species cannot move to cooler climes in time to survive. Camille Parmesan thinks humans should help even if it means creating invasive species

Courtesy of Michael C. Singer

Camille Parmesan didn't mind having her early work denigrated by Rush Limbaugh during his on-air program. "Actually, I was quite pleased with that," she says of the radio show host, who derided her studies on the geographic shifts of a butterfly species because of climate change. "I thought if I got his goat that heavily, then I must be making an impact."

That was in 1996, and since then she has become one of the leading conservation biologists monitoring what rapid climate change is doing to the world's plants and animals. Like many of her colleagues, she warns anyone who will listen of the ecological dangers. But unlike her colleagues, she is lately suggesting a way of saving threatened species that is still unthinkable to many biologists: assisting their migration and colonization.

The controversial approach, she argues, may be the only way to save imperiled species that cannot adapt to the unnatural rate of today's changes or escape to appropriate climes. Transplantation should be done, she says, even if it risks engendering new diseases and pests or other unintended consequences. Some scientists have begun to take her seriously, meeting to discuss the issue and building models that go beyond simple climate projections.

Parmesan did not hold such a view when she published her now famous 1996 study on the plight of Edith's checkerspot butterfly a delicate creature colored with brown, orange and white spots, sometimes no more than a centimeter across. She had spent almost five years trekking into the backcountry along the Pacific coast, from Mexico to Canada, crawling under the insect's plant, a type of snapdragon. Only once did she get chased off the land, in Baja California by someone who acted like "a typical drug lord," she recalls.

The checkerspot is very sensitive to temperature because its host plant dries out in warm temperatures, eliminating the insect's food source while in its caterpillar stage. Scientists already knew that human development and climate were driving down its populations, but Parmesan's systematic science startled everyone: three fourths of the populations at the lowest latitudes had become extinct, whereas only 20 percent of those in Canada had disappeared. Populations at higher altitudes were only one third as likely to go extinct as those at lower, warmer heights.

Soon Parmesan, now at the University of Texas at Austin, noticed similar trends among butterflies in Europe, where records of their domains go back much further. Subsequent analyses conducted with colleagues such as David Easterling of the National Climatic Data Center in Asheville, N.C., and Gary Yohe of Wesleyan University uncovered evidence of climate change nearly everywhere they looked. For instance, plants and animals have shifted their ranges by about six kilometers per decade toward the poles during the past quarter of a century. Spring events, such as blooming, frog breeding and migrant bird arrivals, have advanced 2.3 days per decade. Tropical pathogens are moving up in latitude and striking species not adapted to deal with them. About two thirds of the 110 known harlequin frog species in Costa Rica are believed to be extinct, their temperature-weakened immune systems devastated by a lethal fungus itself taking advantage of warmer temperatures.

Last December scientists announced the probable extinction of the first mammal because of climate change: the white lemuroid possum, now gone from Queens land, Australia. The possum, which lived only above 1,000 meters in altitude, could be killed by as little as five hours in temperatures greater than 30 degrees Celsius (86 degrees Fahrenheit). Although precise predictions are not yet possible, Chris D. Thomas of the University of Leeds in England and his colleagues have found that even under midrange global-warming scenarios, 15 to 37 percent of terrestrial species will be "committed to extinction" by 2050. Add that to existing threats from habitat destruction and migration barriers from towns and highways, and the future of the world's biodiversity looks increasingly thin and vanilla.

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