A few weeks ago, we reported that the rate of abnormalities in frogs and toads was lower than expected but we incorrectly went on to say that fears of an amphibian "die-out" had been disproven by the study.
As often happens, in trying to explain a nuanced, complex scientific study in language accessible to the general-interest public, we reached a conclusion not supported by the study.
In fact, say the scientists who conducted the study, "Localized Hotspots Drive Continental Geography of Abnormal Amphibians on U.S. Wildlife Refuges," frogs and toads are still disappearing from the earth, but they are not displaying as many abnormalities -- missing legs, among others -- as had been expected, at least on National Wildlife Refuges of the U.S. The study identified large areas of the country where abnormal amphibians were rare on refuge lands, but also several places (in California, Alaska and the Mississippi River Valley) that deserve further consideration for higher rates of abnormalities than expected.
"Despite our recent findings regarding abnormal frogs on National Wildlife Refuges, the science of amphibian conservation tells us that frogs are in fact croaking. There is a big difference between abnormalities (what we measured) and amphibian population declines (what we did not measure, but others did)," said Mari K. Reeves, PhD, an ecologist with the U.S. Fish and Wildlife Service in Alaska. "By definition, to measure abnormalities, we need to be able to find frogs. Where frogs are not living any longer is where others have measured a loss of amphibians from areas, indicating population declines."
Reeves told ConsumerAffairs both are important things to measure.
"But they tell you different things," she said. "Abnormalities can tell you where frogs are still present, but they may need some help. Declines tell you where you have lost species from places altogether, something we know is happening worldwide, including in the U.S."
A real issue
"Amphibian population declines are a real issue facing a class of organisms that has been on earth for over 350 million years, and our best research shows them to be extremely imperiled," Reeves said. "Amphibians are key components of ecosystems, both as consumers of algae in aquatic environments and insects on land, and as food for other important wildlife farther up the food chain (like birds, mammals, and snakes). Their loss is transforming habitats globally. They are important and they are imperiled," she said.
Several studies support that assertion, including a 2004 report by the International Union for Conservation of Nature, which estimated that 31.7% of the U.S. amphibian species were in decline. It may, however, be even worse than that, according to a later study -- "Trends in Amphibian Occupany in the United States" -- published in May 2013 in PLOS One.
"Our most interesting (and troubling) finding is probably that even the species that the IUCN categorizes as 'Least Concern' (species they thought were doing OK) were declining at 2.7% per year in our study," said Michael J. Adams, PhD, of the U.S. Geological Survey, who led the study.
"That may not sound like a lot but would result in those species disappearing from half their range in about 27 years if that trend continued," Adams told ConsumerAffairs. "Overall, the trends we documented suggest that amphibian declines may be more widespread and severe than previously thought."
While no single cause has been pinpointed, Adams suggests the obvious candidates include land use change, disease, pollution and global climate change, interacting with each other and with such other factors as habitat degradation and contamination.