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Will the world soon no longer have amphibians? Global populations rapidly decreasing


(NaturalNews) North American amphibian populations are dropping so rapidly that they will have disappeared completely from half of their current habitats within 20 years if the situation does not improve, according to a study led by the U.S. Geological Survey, and published in the journal Scientific Reports.

The findings match overall global trends in amphibian numbers.

Troublingly, the study found that no single cause can be blamed for the crisis. This means there is also no simple solution to the problem. Rather, multi-pronged local, national and global efforts will be needed.

Scientists have known about the ongoing amphibian population crash since the 1960s. Numbers are falling worldwide, including in protected areas such as parks and refuges. A shocking 32 percent of the more than 15,000 animal species threatened with extinction are amphibians.

Causes vary by region

Previous research has firmly established human activity as the cause of the amphibian crisis. In a nutshell, the things humans have been doing to harm the planet – from clearing land for human use, to draining wetlands, to contaminating the environment with toxic chemicals – seem to hit amphibians harder than other animals. In part, this may be because amphibian adults and eggs both have highly absorbent skins that provide little defense against toxic chemicals.

But as the new study shows, the causes are more complex and varied than any one explanation.

The study was the first to look at the varied causes of amphibian decline on a continent-wide scale.

"This study involved a truly comprehensive and collaborative effort to bring together data from researchers across the United States," said lead biometrician, David Miller of Penn State University. "We combined nearly half a million actual observations of 84 species across 61 study areas."

The researchers found that amphibian populations are declining by 3.79 percent per year, confirming the findings of another USGS-led study from 2013. In contrast with that prior study, however, the new study found that the rate of decline is higher in some regions, such as the West Coast and Rocky Mountains.

"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," coauthor Michael Adams said.

The study examined four main threats to amphibian populations: habitat modification by humans, disease, pesticides and climate changes. It found that while all four factors are stressing amphibians continent-wide, the influence of each factor varied dramatically by region.

Habitat modification was most influential east of the Mississippi River, with urban development the culprit in the Northeast, and conversion of land to agriculture to blame in the Midwest. Disease was most influential in New England and the Upper Midwest, while pesticides played the greatest role east of the Colorado River. Changes to climate are placing the greatest stress on amphibians along the West Coast and in the southern United States.

Local conservation actions crucial

Of course, all four causes interact in complex ways to make the outlook for amphibians grim. For example, a large body of research has shown that exposure to pesticides suppresses the immune systems of wildlife (and thus probably of humans). Thus, pesticide-exposed amphibians – who are particularly vulnerable due to their permeable skin and the amount of time they spend in water – become more likely to suffer from the disease outbreaks currently ravaging their populations.

The findings show that amphibian populations cannot be saved by large-scale action alone, the researchers noted.

"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," lead researcher Evan Grant said. "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."

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