Even tropical plant and animal species living in some of the warmest places on Earth may face threats from a warming planet, according to new research co-authored by a UCLA scientist.
Evolutionary biologist Alex Gilman and her colleagues collected data on the altitudinal ranges of nearly 2,000 plant and insect species living on the forested slopes of a Costa Rican volcano that rises some 10,000 feet. They found that about half the species have such narrow altitudinal ranges that a 2,000-foot uphill shift caused by warming temperatures would move them beyond the upper limits of their current ranges. Their research appears Oct. 10 in Science magazine.
The researchers also found that many species may be unable to shift because mountainside forests in the tropics have been severely fragmented by human land use.
Meanwhile, tropical lowland rainforests, the warmest forests on Earth, face a challenge that has no parallel at higher latitudes. If the current occupants of the lowlands shift uphill, tracking their accustomed climate, there are few potential replacements currently living in even warmer places. According to Gilman and her colleagues, the threat of lowland attrition from warming climates could affect about half the species they studied in Costa Rica unless lowland species retain tolerances to higher temperatures developed millions of years ago when the world was much warmer.
"Our research suggests that the effect of global climate change on some tropical rainforest and mountain species could be significant," said Gilman, who earned her doctorate from the UCLA Department of Ecology and Evolutionary Biology while conducting the research. "Only additional research can estimate the risk."
Philip Rundel, UCLA distinguished professor of ecology and evolutionary biology, supervised Gilman's work.
"While the effects of climate change of certain species have been well-documented," he said, "there has been surprisingly little attention given to the effects of a warming climate on tropical plants and animals."
The lead author of the Science magazine study was Robert Colwell, of the University of Connecticut.
As the Earth's climate has warmed in recent decades, the geographical ranges of well-studied bird, butterfly and plant species in the U.S. and Europe have moved northward, following the gradual northward shift of their familiar climates. Other studies have shown that species in the U.S. and Europe have shifted to higher elevations, as temperature zones on mountains have moved upward.
The Science study notes that tropical climates have warmed more than 1.4 degrees Fahrenheit since 1975, and climate models predict an additional increase of nearly 6 degrees over the next century in the tropical forests of Central and South America.
Such warming would shift temperature zones uphill about 2,000 feet. Tropical species, like those at higher latitudes, will likely be driven to higher elevations by these changes, following the climate zones for which they are suited, according to the study.
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