Global warming link to amphibian declines in doubt

Nov 12, 2008

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.

"There is indeed a positive, multi-decade correlation between amphibian extinctions in Latin America and air temperature in the tropics," said Jason Rohr, lead author and assistant professor of biology at University of South Florida. "But this relationship should not necessarily be interpreted as causal."

Rohr and his University of South Florida colleagues Thomas R. Raffel and John M. Romansic, both faculty associates, along with Hudson and Hamish McCallum, professor of wildlife research, University of Tasmania, tested the competing theories by re-analyzing the same data used in conceiving the two ideas.

The team's findings were published in a recent issue of the Proceedings of the National Academy of Sciences. The work is funded by the National Science Foundation.

The scientists checked the first hypothesis to see whether climatic factors such as the percentage of cloud cover, narrowing difference between the lowest average daily temperature and the highest average daily temperature, and the predicted growth rate of the fungus under certain temperatures, could accurately predict extinctions.

Their statistical analysis revealed no such narrowing of temperature spans in the 1980s, when extinctions were increasing. When the difference in average daily temperatures did narrow in the 1990s, amphibian extinctions were decreasing.

Further, while the chytrid-thermal-optimum hypothesis showed high elevations as having the highest proportion of amphibian declines and the second highest proportion of amphibian extinctions, statistical analysis showed that growth rates for the fungus and cloud cover to be lowest at the highest elevation.

"While there is evidence to suggest that the chytrid fungus is killing the frogs, further research is needed before we can conclude that climate change is accelerating the spread," said Rohr, who previously was a researcher with Penn State's Center for Infectious Disease Dynamics.

A separate statistical analysis of the spread hypothesis also indicated inconsistencies between the year of amphibian declines, and the sites from where the fungus might have been introduced.

"Almost all of our findings are contrary to the predictions of the chytrid-thermal-optimum hypothesis," said Hudson.

The researchers say their findings show the pitfalls of drawing conclusions from multi-decadal correlations between climatic factors and extinctions, and underscores the need for molecular data on the fungus to understand from where and how it spread.

"We are facing a cataclysmic global decline in amphibians, caused primarily by the effect of a fungus that was historically not important, but the emergence of which might be associated with climate change, along with the use of herbicides and pesticides," Hudson explained. "The bottom line is that there doesn't seem to be one single explanation for the massive amphibian declines. It could be a mix of other factors."

Source: Penn State

Explore further: Dead floppy drive: Kenya recycles global e-waste

add to favorites email to friend print save as pdf

Related Stories

Researchers try to save huge US salamander (Update)

Jul 10, 2014

With a long, slimy body and beady eyes, North America's largest salamander wouldn't top any cutest animal lists. The hellbender's alien appearance and mysterious ways have earned the big amphibian a bad reputation and unflattering ...

European newts invade Australia

Jun 30, 2014

Once confined behind pet shop windows, the smooth newt (Lissotriton vulgaris) –a 'controlled pest animal' in Victoria – has made a new home in Melbourne's peri urban fringe.

Europe's salamanders at risk from mystery fungus

May 22, 2014

The discovery of dozens of dead salamanders in Belgium in recent weeks is triggering fears that a mystery fungus risks threatening the very survival of the tiny amphibians across Europe.

Researchers help 'extinct in the wild' toad return home

Nov 01, 2012

(Phys.org)—Scientists from the University of Georgia Savannah River Ecology Laboratory have helped to reintroduce a species of toad declared extinct in the wild to its native range-the world's first reintroduction of an ...

Recommended for you

Dead floppy drive: Kenya recycles global e-waste

16 hours ago

In an industrial area outside Kenya's capital city, workers in hard hats and white masks take shiny new power drills to computer parts. This assembly line is not assembling, though. It is dismantling some ...

New paper calls for more carbon capture and storage research

21 hours ago

Federal efforts to reduce greenhouse gas emissions must involve increased investment in research and development of carbon capture and storage technologies, according to a new paper published by the University of Wyoming's ...

Coal gas boom in China holds climate change risks

Aug 22, 2014

Deep in the hilly grasslands of remote Inner Mongolia, twin smoke stacks rise more than 200 feet into the sky, their steam and sulfur billowing over herds of sheep and cattle. Both day and night, the rumble ...

User comments : 10

Adjust slider to filter visible comments by rank

Display comments: newest first

Roach
2.2 / 5 (11) Nov 12, 2008
"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"

Um, yeah, nuff said.

"Almost all of our findings are contrary to the predictions of the chytrid-thermal-optimum hypothesis," said Hudson.

"We are facing a cataclysmic global decline in amphibians, caused primarily by the effect of a fungus that was historically not important, but the emergence of which might be associated with climate change"

It's like they aren't even trying they just blame it on climate change regardless of their results and BAM there's some more grant money.
Velanarris
2.1 / 5 (14) Nov 12, 2008
It looks like the closet AGW skeptics are starting to get the all clear signal to start performing scientific research again.
Velanarris
2.1 / 5 (15) Nov 12, 2008
Also looks like barakn doesn't care to post on articles that are completely contrary to his stance and in turn would rather downrank the article and all of it's supporters without engaging in conversation or debate.

Yep, just like the AGW crowd for the most part. "If it doesn't agree with me, it's wrong."
Noein
3 / 5 (12) Nov 12, 2008
It looks like the closet AGW skeptics are starting to get the all clear signal to start performing scientific research again.


Which researchers mentioned in the above article are "closet AGW skeptics?" Where do they say that they are? Where is there any hint of global warming denialism at all in the entire article?

How does this premise:

"Global warming link to amphibian declines in doubt."

lead to this conclusion:

"Humans contribute nothing to global warming."

?

It's nothing more than denialist desperation, grasping at anything to affirm their deep religious faith in reality denial.

Velanarris
2.5 / 5 (11) Nov 12, 2008
It's nothing more than denialist desperation, grasping at anything to affirm their deep religious faith in reality denial.
I didn't realize that AGW was proven...

Oh wait, it isn't. You're wearing the zealot role far better than I can.

I call for research, you call for silence. I ask for proof, you call me a denialist.

Get your broomsticks, it's shenannigans.
jeffsaunders
4.1 / 5 (7) Nov 12, 2008
I like frogs and I like science. Fungus, I guess it has its uses.

So?, let us find out what we can do to save what frogs are left. Maybe it will take real science to do this. I am in favour of real science. Possible conclusions can be drawn before all the facts are in, but let us remember that a possible conclusion is nothing more than a guess based on gut instinct.

Guesses can be influenced by peer pressure. Regardless of the guesses, basic research should be aimed at finding facts which can be built upon, not more guesses.

Amphibians have been around since long before dinosaurs, that does not mean they deserve to go. We may not be able to hold the world exactly as it is now forever but you can be sure that if this fungus is killing the frogs then people are transporting the fungus around the world.
MikeB
2.5 / 5 (8) Nov 14, 2008
So true, unscrupulous people have established a world trade route in this batrachian fungus. The leaders of this sinister plot have dosed shoe components in China with the spore, and are even now devising schemes to entice the unwitting wearers of those shoes to frequent the types of watery ecosystems that our amphibious brethren prefer.
SAVE THE FROGS! Buy American shoes.
GrayMouser
3.4 / 5 (5) Nov 14, 2008
So true, unscrupulous people have established a world trade route in this batrachian fungus. The leaders of this sinister plot have dosed shoe components in China with the spore, and are even now devising schemes to entice the unwitting wearers of those shoes to frequent the types of watery ecosystems that our amphibious brethren prefer.
SAVE THE FROGS! Buy American shoes.


No wonder my feet keep itching!
MikeB
1.8 / 5 (5) Nov 16, 2008
THERE IS A FUNGUS AMUNGUS!!!!AHHHHHHH!!!
barakn
3 / 5 (4) Nov 30, 2008
Also looks like barakn doesn't care to post on articles that are completely contrary to his stance and in turn would rather downrank the article and all of it's supporters without engaging in conversation or debate.

I gave the article a 4 or 5, IIRC. The article strengthened my suspicion that amphibian decline has multiple sources. What stance are you referring to?