For the first time, scientists have documented a link between global warming — perhaps better described as human-induced climate disruption — and the significant loss of amphibian biodiversity. Alan Pounds, an ecologist at the Tropical Science Center’s Monteverde Cloud Forest Preserve in Costa Rica, led a team of 14 scientists that investigated the disappearance of more than 70 species of harlequin (Atelopus sp.) frogs in Central and South America. More than half of these frog species have gone extinct.
Researchers had identified the chytrid fungus Batrachochytrium dendrobatidis as the villain wiping out harlequin frogs, but until this study, published in the journal Nature, no one knew why the fungus had taken such a toll. Pounds’ team found the major culprit to be rising tropical temperatures and shifting weather patterns. “Disease is the bullet killing frogs, but climate change is pulling the trigger,” Pounds says. The researchers found that, more than 80 percent of the time, higher tropical temperatures corresponded to the disappearance of Atelopus species. After one unusually warm year, 1987, five species were lost.
From 1975 to 2000, average temperatures in the American tropics rose three times faster than the rate for the planet over the entire 20th century. This drastic increase has resulted in more water evaporation, less mist and a higher, thicker cloud cover in the region. The heavy clouds block enough sunlight to keep daytime temperatures lower than normal. But at night, the cloud cover prevents heat from escaping the atmosphere, leading to higher temperatures. The researchers argue that this combination of daytime cooling and nighttime warming creates an ideal environment for the chytrid fungus to thrive. Normally, this region is subject to temperature extremes that keep the fungus in check.
The researchers used satellite imaging to check for deforestation and concluded with “very high confidence” that global warming — not the destruction of habitat — has led to the simultaneous demise of harlequin frogs in diverse habitats. Arturo Sanchez-Azofeifa, one of the study’s authors, says there is “absolutely a linkage between global warming and this disease — they go hand-in-hand.”
Because amphibians have moist, permeable skin, they are highly sensitive to environmental change — even to minor shifts in temperature, humidity or water quality — and thus are unique indicators of ongoing climate disruption. The deadly chytrid fungus attacks the lunglike skin of these frogs and kills them.
Sanchez-Azofeifa is worried that too much of the climate change discussion concerns industrialized areas. Meanwhile, extremely sensitive ecosystems — such as tropical forests — receive little attention.
Shifting temperatures and weather patterns — caused by the burning of fossil fuels and other human activities — endanger plants and animals worldwide. According to Pounds’ team, “Climate-driven epidemics are an immediate threat to biodiversity ... the urgency of reducing greenhouse gas concentrations is now undeniable.”
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