‘No comfort in knowing’ El Niño and a pathogen, not global warming, caused Costa Rica golden toad extinction

ScienceDaily (Mar. 2, 2010) — Scientists broadly agree that global warming may threaten the survival of many plant and animal species; but global warming did not kill the Monteverde golden toad, an often cited example of climate-triggered extinction, says a new study. The toad vanished from Costa Rica’s Pacific coastal-mountain cloud forest in the late 1980s, the apparent victim of a pathogen outbreak that has wiped out dozens of other amphibians in the Americas. Many researchers have linked outbreaks of the deadly chytrid fungus to climate change, but the new study asserts that the weather patterns, at Monteverde at least, were not out of the ordinary. The role that climate change played in the toad’s demise has been fiercely debated in recent years. The new paper, in the March 1 issue of the Proceedings of the National Academy of Sciences, is the latest to weigh in. In the study, researchers used old-growth trees from the Monteverde Cloud Forest Reserve to reconstruct moisture levels in that region over the last century. They expected to see global warming manifested in the form of a long-term warming or drying trend, but instead discovered that the forest’s dry spells closely tracked El Niño, the periodic and natural warming of waters off South America that brings drought to some places and added rainfall and snow to others. The golden toad vanished after an exceptionally dry season following the 1986-1987 El Niño, probably not long after the chytrid fungus was introduced. Scientists speculate that dry conditions caused the toads to congregate in a small number of puddles to reproduce, prompting the disease to spread rapidly. Some have linked the dry spell to global warming, arguing that warmer temperatures allowed the chytrid pathogen to flourish and weakened the toad’s defenses. The new study finds that Monteverde was the driest it’s been in a hundred years following the 1986-1987 El Niño, but that those dry conditions were still within the range of normal climate variability. The study does not address amphibian declines elsewhere, nor do the authors suggest that global warming is not a serious threat to biodiversity. “There’s no comfort in knowing that the golden toad’s extinction was the result of El Niño and an introduced pathogen, because climate change will no doubt play a role in future extinctions,” said study lead author Kevin Anchukaitis, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory. …

El Niño and a pathogen, not global warming, killed Costa Rican toad