Where Have All the Amphibians Gone?
The world’s frogs, toads and salamanders are in serious trouble. In fact, amphibian populations are not just declining, they’re in free fall. Incredibly, some could be headed for extinction by 2033.
That was the disturbing conclusion of a first-of-its-kind study released by the U.S. Geological Service in late May. USGS calls this study the first “continental-scale estimate of a yearly rate at which the United States is losing amphibian populations and subpopulations.”
Scientists from the USGS Amphibian Research and Monitoring Initiative (ARMI) reviewed data on 48 amphibian species collected between 2002 and 2011 from 34 sites around the country. Though the ARMI researchers expected to find some species doing well, or at least better, the nine-year study instead found “a declining trend in every subset of data examined.”
The USGS study was published in the journal PLOS One.
Nearly a third of the earth’s amphibians — 1,856 species — are considered threatened, according to a recent assessment. Over the past 20 years, it is estimated that 168 species have become extinct, while nearly 2,500 more are declining in number.
Amphibians make particularly instructive subjects for study because their well being accurately reflects the overall health of the ecosystem in which they live. They sit squarely in the center of the food chain. Their permeable skin makes them especially sensitive to environmental disruptors. If something goes badly awry for amphibians, their woes are considered a warning bell for all other creatures.
That warning bell is ringing. Loudly. The USGS study revealed that frogs, toads and salamanders are disappearing from their habitats at an average rate of about 3.7 percent per year. Left unchecked, that rate of disappearance means that these species will be extinct within half of their current habitats within 20 to 26 years.
Worse yet, amphibian species classified as “threatened” are vanishing at a rate of 11.6 percent per year. They are expected to disappear from half of their habitats within a mere six years.
The ARMI research study did not evaluate the underlying causes of the declining amphibian population. However, many scientists believe that a combination of factors including disease, pesticide use, invasive species encroachment, habitat loss and climate change may be to blame.
This is “very bad news for amphibians,” according to Brian Gratwicke, amphibian conservation biologist with the Smithsonian Conservation Biology Institute. “Now, more than ever, we need to confront amphibian declines in the U.S. and take actions to conserve our incredible frog and salamander biodiversity.”
What’s especially concerning about this situation is that these precipitous declines in population are occurring even on lands that are ostensibly protected areas, such as wildlife refuges and national parks.
“We knew there was a big problem with amphibians, but these numbers are both surprising and of significant concern,” said USGS ecologist and lead study author Michael Adams.
He added that the fact that amphibian population losses “are occurring in our most protected areas adds weight to the hypothesis that this is a global phenomenon with implications for managers of all kinds of landscapes, even protected ones.” Unexpectedly, researchers found a higher rate of decline on National Park Service lands compared to other types of land monitored during the study, but it was not clear why this should be so.
According to USGS Director Suzette Kimball, up to now, amphibians have been able to survive “countless changes that caused many other groups of animals to go extinct.” She believes the findings of this study are noteworthy because it’s clear “that the pressures amphibians now face exceed the ability of many of these survivors to cope.”
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