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Butterflies Head North to Beat the Rising Heat

Climate: Researchers say they have found the first biological consequence of global warming as insects shift to cooler habitats.

August 29, 1996|ROBERT LEE HOTZ | TIMES SCIENCE WRITER

In what experts are calling the first direct biological consequence of global warming, a delicate species of butterfly is being driven north through California to escape rising temperatures, a researcher at UC Santa Barbara reported Wednesday.

Known as Edith's checkerspot butterfly, the insect is prized by collectors for the distinctive orange and black patterns on its wings--which, folded together, are the size of a pair of postage stamps--and by ecologists because it is especially sensitive to subtle climate changes.

The butterfly is rarely noticed among the hillside snapdragons and figworts on which it feeds, but it can be found at sites from Mexico to Canada--often living and dying confined to a habitat no larger than a few hundred square yards.

Camille Parmesan, a research fellow at the university's National Center for Ecological Analysis and Synthesis, surveyed 151 locations throughout western North America where the butterfly traditionally flourished.

In research published in the journal Nature, she found that rising temperatures were killing off the butterfly at the southern extremes of its range, while at the same time allowing it to expand into cooler climes to the north. Populations in Mexico were four times as likely to be extinct as those in Canada, Parmesan discovered.

She also found that in those southern areas where the butterflies persisted, the insects had shifted to higher elevations, where temperatures were slightly cooler.

"It is an excellent climate sensor--a canary in a coal mine," said Stanford University ecologist Paul Erlich, who also has studied the butterfly. "This is one of the first and best signs that we may be getting climate change and of the biological effects of what may be a human-induced climate change."

There is broad agreement among scientists that the Earth has gotten warmer by, on average, at least 1 degree during the past century. But there is considerable controversy over what, if any, effect the Earth's changing climate has had on flora and fauna.

"This indication that biological change is afoot is not just a matter for idle curiosity," said Chris D. Thomas, a senior biologist at the University of Leeds in England. "There are major implications for agriculture, medicine and conservation. This may mean major shifts in where we grow our crops, where pests live, where diseases occur, where endangered species might be able to survive."

Until now, biological effects of climate change have been detected only through very limited field studies, greenhouse experiments or indirect measures of biological activity.

Several computer models of global warming predict that climate-sensitive animals and plants will shift northward or to higher elevations in response to rising temperatures.

It was those predictions that Parmesan set out to test in a study funded by NASA's Mission to Planet Earth, which documents global change. The tiny butterfly that she cataloged was an excellent test case because it has been intensively studied and collected for more than 35 years. She logged 45,000 back-road miles during the three-year study.

Parmesan took pains to exclude areas where the butterfly had been wiped out by the effects of overgrazing, land clearing, logging, construction or the introduction of new plant species that might have forced out the flowers that the butterflies feed on.

"I was interested in natural extinctions, not extinctions caused by mankind," she said.

"I found this very striking pattern. They really are going extinct much more rapidly at the southern end of their range than at the northern end," she said. "It is exactly what climate warming models predict."

The result, she said, "is the clearest indication to date that global climate warming is already influencing species' distribution."

John Harte, an expert at UC Berkeley on the biological effects of climate change, said her study appears to confirm the prevailing theory of how global warming will alter wildlife. Harte, however, believes that most plants and animals rely on too many local factors, from soil microbes to air quality, to simply shift northward.

"If her study is true, it really points to the validity of the conventional and, to my mind, implausible picture of how plants and animals will respond to climate change," he said. "I think it is exciting, thought-provoking work."

Until this study, no one had examined how a species was reacting to warmer temperatures across the entire range of its habitats.

Last year, researchers at the Monterey Bay Aquarium Research Institute reported that entire populations of sea creatures, including snails, crabs, starfish and anemone, were migrating north in reaction to rising ocean temperatures over a 60-year period. But researchers only studied one tide pool in Monterey Bay.

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