WASHINGTON, March 25 (Xinhua) -- Wild salamanders living in some of North America's best salamander habitat are getting smaller due to global warming, a U.S. study said Tuesday.
The study, published in the journal Global Change Biology, said the salamanders are forced to burn more energy as their surroundings get warmer and drier.
Scientists have predicted that some animals will get smaller in response to climate change, and this is strong confirmation of that prediction, the researchers said.
The study examined museum specimens caught in the Appalachian Mountains from 1957 to 2007 and wild salamanders found at the same sites in 2011 and 2012.
The salamanders studied from 1980 onward were, on average, eight percent smaller than their counterparts from earlier decades, the study said.
Overall, six salamander species got significantly smaller, while only one got slightly larger between 1957 and 2012, it said. On average, each generation was one percent smaller than its parents' generation.
The researchers also compared changes in body size to the animals' location and their sites' elevation, temperature and rainfall. They found the salamanders shrank the most at southerly sites, where temperatures rose and rainfall decreased over the 55- year study.
"This is one of the largest and fastest rates of change ever recorded in any animal," said Karen Lips, an associate professor of biology at the University of Maryland and the study's senior author.
"We don't know exactly how or why it's happening, but our data show it is clearly correlated with climate change," she said.
To find out how climate change affected the animals, the researchers used a computer program to create an artificial salamander, which allowed them to estimate a typical salamander's daily activity and the number of calories it burned.
The simulation showed the modern salamanders were just as active as their forbears had been. But to maintain that activity, they had to burn seven to eight percent more energy. That's because cold-blooded animals' metabolisms speed up as temperatures rise, they explained.
To get that extra energy, salamanders must make trade-offs, Lips said. They may spend more time foraging for food or resting in cool ponds, and less time hunting for mates. The smaller animals may have fewer young, and may be more easily picked off by predators.
"Right now we don't know what this means for the animals," Lips said. "If they can start breeding smaller, at a younger age, that might be the best way to adapt to this warmer, drier world. Or it may be tied in with the losses of some of these species."
The research team's next step will be to compare the salamander species that are getting smaller to the ones that are disappearing from parts of their range.