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If they all hop at the same time … Which way will they go

Evidence that global warming is causing the worldwide declines of amphibians may not be as conclusive as previously thought, according to biologists. The findings, which contradict two widely held views, could help reveal what is killing the frogs and toads and aid in their conservation.

“We are currently in the midst of a sixth mass extinction event,” said Peter Hudson, the Willaman professor of biology at Penn State and co-author of the research study. “And amphibians are bearing the brunt of the problem.”

Studies suggest that more than 32 percent of amphibian species are threatened and more than 43 percent face a steep decline in numbers.

Much of the massive declines associated with amphibians appear to be centered in places such as Central America and Australia, said Hudson. “It appears to be linked to a chytrid fungus — Batrachochytrium dendrobatidis (Bd) — which we did not know affected frogs,” he added.

There are currently two theories on the extinctions. The first — chytrid-thermal-optimum hypothesis — suggests that the declines were triggered by global warming which pushed daytime and nighttime temperatures to converge to levels that are optimal for the growth of the chytrid fungus.

But according to a second theory — spatiotemporal-spread hypothesis — amphibian declines were simply driven by the introduction and subsequent spread of the fungus from certain locations.

“Our models suggest that both these theories are slightly wrong,” added Hudson, director of the Huck Institutes of the Life Sciences at Penn State. “Neither of them fit available data.”

While the researchers do not completely discount the role of global warming in amphibian declines, they believe that evidence linking it with the declines is weak.

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