Yellowstone Amphibians Declining Under Climate Change
Discovery.com, Oct. 27, 2008
Despite being protected longer than anywhere else on Earth, Yellowstone's amphibians are declining fast. The culprit, say researchers: climate change.
In 1992 and 1993, researchers in Elizabeth Hadly's group at Stanford University surveyed amphibians dwelling in ponds left behind by glaciers in northern Yellowstone National Park. Over the last three summers, Hadly's graduate student Sarah McMenamin repeated the study.
McMenamin looked for the four species of amphibians found in the park -- a salamander, two frogs and a less common toad -- in 49 ponds, counting even the presence of one member of a given species in a particular pond as a "population." Fewer than half of the populations recorded in the 1992 survey remained 15 years later.
"I found that not only had a lot of the amphibian populations disappeared from the ponds, but the ponds themselves were disappearing," McMenamin said.
Nineteen of 49 ponds that were either permanent or seasonally full in 1992 and 1993 were dry in 2006 and 2007, although 11 of them filled again in 2008, the third wettest spring on record. Amphibians returned to only six of the refilled ponds.
"This is really catastrophic to the local amphibian population, because obviously they need these environments to breed and exist as larvae," McMenamin said.
Climate records over the last 60 years show a strong trend of increasing temperature and decreasing precipitation, she added.
"We were just blown away," Hadly said of the findings, published in the Proceedings of the National Academy of Sciences. "Sixteen years is so fast. It's an effect on the entire amphibian community distributed all across this landscape."
The fact that this happened in Yellowstone made it easy to rule out other impacts.
"It's not that there's an exotic species invasion. It's not that there are human impacts like plowing or irrigation. It's not like direct habitat degradation due to humans has any role to play here," Hadley said. "There's nothing upstream in this place except mountains and water."
"Our study shows that even an area as protected as Yellowstone is not immune to the effects of climate change," McMenamin added. Yellowstone National Park, founded in 1872, has been protected by law longer than anywhere else in the world.
Amphibian declines been reported worldwide, with many pointing to disease, especially a type of chytrid fungus, as a major cause.
McMenamin saw evidence of disease on two occasions in her survey. Rising temperatures and drying ponds may create stressful conditions that make amphibians more susceptible to infection, she added: "It's a triple whammy on the amphibians."
"I was surprised by the magnitude of change," said evolutionary biologist David Wake of the University of California, Berkeley. "This paper coupled with some others that have appeared in the past weeks on climate change and its impact make it clear that climate change is a problem not only for the future, but right now."
"This is the strongest scientific evidence I've seen on the climate changes in Yellowstone," added John Varley, director of Montana State University's Big Sky Institute in Bozeman. "Many believe they see changes, but this paper is solid proof."