USF Biologists Link El Niño, Temperature Variability to Amphibian Declines

Investigating Amphibian Declines

Tuesday, April 20, 2010 - News

USF Biologists Link El Niño, Temperature Variability to Amphibian Declines

By Vickie Chachere

TAMPA, Fla. (April 19, 2010) – Two University of South Florida biologists investigating worldwide amphibian declines found evidence that increased temperature variability during El Niño climatic events might drive amphibian extinctions by reducing their defenses against pathogens.

Researchers Jason Rohr and Thomas Raffel found that climate change might exacerbate amphibian declines by increasing their susceptibility to disease. Their findings, published in The Proceedings of the National Academy of Sciences, suggest “that changes to temperature variability associated with climate change might be as significant to biodiversity losses and disease emergences as changes to mean temperature”. The research was funded by U. S. Environmental Protection Agency, Department of Agriculture, and National Science Foundation grants.

The contributions of climate change to species extinctions and the emergence of infectious diseases remain controversial. This debate has been particularly heated for the reerslationship between climate and amphibian declines putatively caused by the deadly amphibian chytrid fungus. According to Rohr and Raffel, this controversy might be partly due to how understudied the effects of climate variability are on species interactions.

Rohr and Raffel used regional estimates of climate averages and variability to test among several climate-related hypotheses for the timing of amphibian extinctions in Latin America. They discovered a clear climatic footprint on extinctions, but only after controlling for the overall multi-decadal trends in these variables.

Raffel states: “The general increase in amphibian extinctions in the 1980’s, probably due to epidemic disease spread, concealed the effect of El Niño, which correlates with short-term fluctuations around the overall extinction trend. Furthermore, fewer variables correlate with these short-term fluctuations than with the multi-decadal increase in extinctions, so these results provide more support for a causal relationship between climate and declines than was available previously.”

Of the 26 tested variables, only temporal variability in temperature could predict annual levels of amphibian extinctions and was consistent with altitudinal and seasonal patterns of declines caused by the amphibian chytrid fungus. These results are consistent with previous findings that temperature variability can compromise amphibian immune defenses, and that disease outbreaks frequently occur during extreme temperature events.

An important remaining question is how general these findings are to other cold-blooded hosts, including insect vectors of human diseases. According to Rohr, “we suspect that the inherent difference in size and metabolism between parasites and hosts allows parasites to acclimate more rapidly to temperature shifts, tipping the balance toward parasites in a climatically more variable world.”

Climate modeling suggests that temperature variability in tropical and subtropical regions and the frequency of Central Pacific El Niño events will increase with projected climate change. Hence, Rohr and Raffel believe that global climate change might contribute to increases in tropical, and perhaps worldwide, enigmatic amphibian declines. Furthermore, amphibian chytridiomycosis might be consistent with the conventional, though controversial, wisdom that climate change will increase infectious diseases.

“Whether variability in temperature generally increases disease remains to be tested,” says Rohr, “but temperature variability might represent a common and under-appreciated link between climate change, disease risk, and biodiversity losses.”

The full text of their study can be found http://www.pnas.org/content/early/2010/04/14/0912883107.full.pdf+html">here.

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