USF Researchers Evaluate Climate Change and Amphibian Decline Links

Tampa, Fla. (Oct. 27, 2008) – In a study just published in the Proceedings of the National Academy of Sciences online Early Edition, University of South Florida biologist and assistant professor Jason Rohr, and colleagues, evaluated competing hypotheses for worldwide amphibian declines, many of which have been caused by the amphibian chytrid fungus, possibly the most deadly invasive species on the planet behind humans.

Rohr and colleagues confirmed that the pattern of amphibian extinctions was consistent with the introduction and spread of this fungus and was positively correlated with increased temperatures associated with global warming. However, Rohr and colleagues concluded that the evidence that global warming actually caused the extinctions is weak. The research was funded by National Science Foundation and Environmental Protection Agency grants.

“We are in the midst of a sixth mass extinction event and amphibians, the most threatened vertebrate taxon on the planet, have become the ‘poster child’,” said Rohr. “More than 32 percent of amphibian species are threatened and more than 43 percent are experiencing some form of population decline. Unlike past mass extinctions, this one is driven by human activities.”

Previous high profile research on amphibian declines suggested that global climate change was causing amphibian declines by improving growth conditions for the deadly chytrid fungus. Competing researchers argued that there was no positive relationship between increased air temperature and amphibian extinctions.

Rohr said, “There is indeed a positive, multi-decade correlation between amphibian extinctions in Latin America and air temperature in the tropics, but this relationship should not necessarily be interpreted as causal.”

Rohr and colleagues’ analyses revealed that temperature-dependent chytrid growth could not explain the pattern of amphibian extinctions, that climate change appears to be reducing, rather than increasing, the growth of this cold-tolerant pathogen, and that many variables were better positive predictors of the timing of amphibian extinctions than air temperature, including ones as far-fetched as beer production.

“There are many convincing examples of the consequences of modern climate change that signify the urgency to curb global warming,” said Rohr. “While there is evidence that disease is the ‘bullet’ killing frogs, further research will be needed before we can conclude that climate change is pulling the ‘trigger.’”

The researchers, however, do believe that climate change could be an important contributor to amphibian declines.

“We hope that our findings clarify factors involved in losses of amphibians and, most importantly, facilitate their protection,” Rohr concludes.

The University of South Florida is one of the nation's top 63 public research universities and one of 39 community-engaged, four-year public universities as designated by the Carnegie Foundation for the Advancement of Teaching. USF was awarded more than $360 million in research contracts and grants in FY 2007/2008. The university offers 219 degree programs at the undergraduate, graduate, specialist and doctoral levels, including the doctor of medicine. The university has a $1.8 billion annual budget, an annual economic impact of $3.2 billion, and serves more than 46,000 students on campuses in Tampa, St. Petersburg, Sarasota-Manatee and Lakeland. USF is a member of the Big East Athletic Conference.

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