Why Are the Frogs Croaking?

According to a 1994 publication by the Global Amphibian Assessment (a collaboration among scientists from IUCN-The World Conservation Union, Conservation International, and NatureServe), nearly one third of the world’s frogs, toads, salamanders, and other amphibians are threatened with extinction. Frogs are “croaking” at an alarming rate. For example, two thirds of the 110 species of harlequin frogs that once lived in the Central and South American tropics have disappeared since the 1980s, and the Monteverde harlequin frog and the golden toad disappeared from the cloud forests of Costa Rica 17 years ago. These particular extinctions are the focus of a recent study coauthored by Professor Chris Still in the prestigious journal Nature. The January 12 (vol. 439) article, Widespread amphibian extinctions from epidemic disease driven by global warming, puts forward evidence that global warming is causing outbreaks of an infectious disease in the mountains of Costa Rica that is wiping out entire populations of frogs. According to the abstract:

As the Earth warms, many species are likely to disappear, often because of changing disease dynamics. Here we show that a recent mass extinction associated with pathogen outbreaks is tied to global warming. Seventeen years ago, in the mountains of Costa Rica, the Monteverde harlequin frog (Atelopus sp.) vanished along with the golden toad (Bufo periglenes). An estimated 67% of the 110 or so species of Atelopus, which are endemic to the American tropics, have met the same fate, and a pathogenic chytrid fungus (Batrachochytrium dendrobatidis) is implicated. Analysing the timing of losses in relation to changes in sea surface and air temperatures, we conclude with ‘very high confidence’ (.99%, following the Intergovernmental Panel on Climate Change, IPCC) that large-scale warming is a key factor in the disappearances. We propose that temperatures at many highland localities are shifting towards the growth optimum of Batrachochytrium, thus encouraging outbreaks. With climate change promoting infectious disease and eroding biodiversity, the urgency of reducing greenhouse-gas concentrations is now undeniable.

To quote J. Alan Pounds, the article’s lead author and the Resident Scientist at the Monteverde Cloud Forest Preserve in Costa Rica, “Disease is the bullet killing frogs, but climate change is pulling the trigger…Global warming is wreaking havoc on amphibians, and will cause staggering losses of biodiversity if we don’t do something fast.” The Nature article concludes by stating that “We establish that global climate change is already causing the extinction of species. Taking our results and recent findings that tie the same losses to disease, we conclude that climate-driven epidemics are an immediate threat to biodiversity…The case illustrates how greenhouse warming and the resultant intensification of the hydrological cycle, together with aerosol pollution, may affect life on Earth. Influencing patterns of cloud formation, these agents alter the thermal, light and moisture environments of many organisms, changing ecological interactions and threatening species survival.” For a pdf of the complete article, click here.

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