Trouble in paradise: Warming a greater danger to tropical species

This leaf beetle, which lives in the cloud forest on the east slope of the Andes Mountains in Ecuador, is from the family Chrysomelidae. Climate change could have a much... Click here for more information.

Polar bears fighting for survival in the face of a rapid decline of polar ice have made the Arctic a poster child for the negative effects of climate change. But new research shows that species living in the tropics likely face the greatest peril in a warmer world.

A team led by University of Washington scientists has found that while temperature changes will be much more extreme at high latitudes, tropical species have a far greater risk of extinction with warming of just a degree or two. That is because they are used to living within a much smaller temperature range to begin with, and once temperatures get beyond that range many species might not be able to cope.

"There's a strong relationship between your physiology and the climate you live in," said Joshua Tewksbury, a UW assistant professor of biology. "In the tropics many species appear to be living at or near their thermal optimum, a temperature that lets them thrive. But once temperature gets above the thermal optimum, fitness levels most likely decline quickly and there may not be much they can do about it."

Arctic species, by contrast, might experience temperatures ranging from subzero to a comparatively balmy 60 degrees Fahrenheit. They typically live at temperatures well below their thermal limit, and most will continue to do so even with climate change.

"Many tropical species can only tolerate a narrow range of temperatures because the climate they experience is pretty constant throughout the year," said Curtis Deutsch, an assistant professor of atmospheric and oceanic sciences at the University of California, Los Angeles. "Our calculations show that they will be harmed by rising temperatures more than would species in cold climates.

"Unfortunately, the tropics also hold the large majority of species on the planet," he said.

Tewksbury and Deutsch are lead authors of a paper detailing the research, published in the May 6 print edition of the Proceedings of the National Academy of Sciences. The work took place while Deutsch was a UW postdoctoral researcher in oceanography.