for National Geographic News
Global warming may cause widespread amphibian extinctions by triggering lethal epidemics, a new study reports.
J. Alan Pounds and colleagues suggest that many harlequin frog species (Atelopus) across Central and South America have disappeared due to deadly infectious diseases spurred by changing water and air temperatures.
"Disease is the bullet killing frogs, but climate change is pulling the trigger," said Pounds, lead study author and resident scientist at Costa Rica's Monteverde Cloud Forest Preserve.
"Global warming is wreaking havoc on amphibians and will cause staggering losses of biodiversity if we don't do something fast."
Biodiversity refers to the number of species in a given area. It is often used to gauge the health of an ecosystem.
The study appears in today's issue of the journal Nature.
About two-thirds of the 110 known harlequin frog species are believed to have vanished during the 1980s and 1990s. The primary culprit, Pounds suggests, is the disease-causing chytrid fungus Batrachochytrium dendrobatidis.
Amphibian skin is extremely thin, which makes frogs acutely sensitive to even minor changes in temperature, humidity, and air or water quality. It also makes frogs more susceptible to chytrid fungus.
The new study suggests that temperature extremes may have previously helped keep the deadly disease in check. But new climate cycles are now moderating those annual temperature swings.
Global warming has increased evaporation in the tropical mountains of the Americas, which in turn has promoted cloud formation, the study reports. That cloud cover may have actually decreased daytime temperatures by blocking sunlight. At the same time, it may have served as an insulating blanket to raise nighttime highs.
Pounds believes the combination has created ideal conditions for the spread of the frog-killing fungus, which grows and reproduces best at temperatures between 63° and 77°F (17° and 25°C).