USGS scientists sound another warning on amphibian extinctions

boreal toad
The last living boreal toad found 2006 in the Cucumber Gulch wetlands in Breckenridge, Colorado. @bberwyn photo.

Focused local conservation efforts needed to stem slow the rapid decline

Staff Report

In an era that’s already being defined by an unprecedented global rate of species extinctions, the amphibian die-off is especially troubling, and the trend continues unchecked, according to a new study led by the U.S. Geological Survey.

And for now, there is no smoking gun pointing to a single reason for the decline. That means there’s no easy answer, either, the scientists said, explaining that, across the U.S. there are multiple and geographically diverse factors that play role.

A 2013 study found that pesticides may be linked with die-offs of amphibians, bats and birds because the toxic chemicals suppress immunity. More recently, researchers identified a new invasive fungus that threatens salamanders in the U.S., and yet another study said pollution and climate change are key threats to amphibians. In Spain, a newly discovered virus is taking toll on amphibians.

“Implementing conservation plans at a local level will be key in stopping amphibian population losses, since global efforts to reduce or lessen threats have been elusive,” said Evan Grant, the USGS research wildlife biologist who led the study. This research changes the way we need to think about amphibian conservation by showing that local action needs to be part of the global response to amphibian declines, despite remaining questions in what is causing local extinctions.”

Published in the journal Scientific Reports, the findings show that every region in the U.S. continues to lose amphibians, with hot spots along the West Coast and in the Rocky Mountains. But the threats differ among regions, including:

  • Human influence from the Mississippi River east, including the metropolitan areas of the Northeast and the agricultural-dominated landscapes of the Midwest
  • Disease, particularly a chytrid fungus in the Upper Midwest and New England
  • Pesticide applications east of the Colorado River
  • Climate changes across the Southern U.S. and the West Coast

The decline is happening even in protected areas like parks and refuges, and has been observed since at least the 1960s. Previous research has generally linked identified environmental factors like climate, human influence such as land-use change, and contaminants and disease, but have not been able to use actual scientific data on a large scale to discern causes of the ongoing disappearance of amphibian populations.

The new study is the first to test this linkage at a continental scale, and finds that the presence and intensity of the four main threats – human influence, disease, pesticide application, and climate change varies substantially across the US. The causes of the declines are more variable — and more locally driven — across the United States than had been assumed.

For example, the research provides evidence that the average decline in overall amphibian populations is 3.79 percent per year, which supports previous USGS-led research findings from 2013 that showed a similar rate of loss. If this rate remains unchanged, these species would disappear from half of the habitats they occupy in about 20 years.

“Losing 3 or 4 percent of amphibian populations might not sound like a big deal but small losses year in and year out quickly lead to dramatic and consequential declines,” said USGS ecologist Michael Adams, a study coauthor and the lead for the USGS Amphibian Research and Monitoring Initiative, which studies amphibian trends and causes of declines.

David Miller, a professor at Penn State University and the lead biometrician in the study, summarized the extent of the effort.

“This study involved a truly comprehensive and collaborative effort to bring together data from researchers across the United States,” Miller said. “We combined nearly half a million actual observations of 84 species across 61 study areas to answer questions about the causes of wide-scale amphibian declines.”

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