Frogs, toads, salamanders and other amphibians are less commonly found today in the United States than they were nine years ago, according to a new study from the USGS Amphibian Research and Monitoring Initiative (ARMI).
The study looked at the rate of change in “occupancy” — the number of ponds, lakes, and other habitat features that amphibians occupied over time. In other words, how fast populations of amphibians were disappearing across the landscape. On average, populations of amphibians vanished from habitats at a rate of 3.7 percent each year.
“Even though these declines seem small on the surface, they are not,” said USGS ecologist Michael Adams, the lead author of the study. “Small numbers build up to dramatic declines with time. We knew there was a big problem with amphibians, but these numbers are both surprising and of significant concern.”
“This is our first good look at long-term trends across the board for amphibian species in the U.S.,” says Robert Fisher, a study coauthor and biologist with the USGS Western Ecological Research Center. “We looked at data for 48 species at 34 sites across the country from nine years and counting, and unfortunately this is the trend the data revealed — even for areas like national parks and national wildlife refuges, and for species we usually consider as stable and widespread.”
The amphibian declines within protected areas suggest that some stressors like diseases or drought are not limited by man-made boundaries. But national parks and wildlife refuges will remain important assets for managers and scientists, providing a testbed to study the extinction factors that transcend protected and unprotected landscapes.
Scientists say the next step is to clarify the factors driving declines in each species. Habitat loss and the continued spread of the “chytrid” fungus are two factors causing amphibian mortality in the U.S. and worldwide. But locally, each species may be experiencing unique factors for population loss.
“For example, in southern California, Sierra Madre yellow-legged frogs and California red-legged frogs are impacted by ash and debris flows from wildfires, which are increasing,” says Fisher. “Overall, it’s just pretty significant to realize that something people generally take for granted — seeing frogs and salamanders around ponds and creeks — might not be a sure thing in the future.”
The study data were collected with help from other federal agencies, including the U.S. Fish and Wildlife Service, Bureau of Land Management, National Park Service, USDA Forest Service and the Department of Defense. Many other partners, including state and local agencies, also played a critical role in this program. The USGS ARMI program was chartered in 2000 by a congressional mandate to study the troubling amphibian declines in the U.S. and around the world.
-- Ben Young Landis
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