Frogs and Toads in Trouble

Emily Guerin | Jun 03, 2013
www.hcn.org/blogs/goat/frogs-and-toads-in-trouble


There hasn’t been a lot of feel-good amphibian news lately (except this video of a happy toad getting a back scratch www.youtube.com/watch?v=MwF3xXm2Qjg ) as increasing numbers of frogs and toads succumb to mysterious ailments. Now, we have a way to quantify all that doom and gloom, thanks to a new study in the online journal Plos One.

Researchers at the U.S. Geological Survey found that every year between 2002 and 2011, frogs and toads disappeared from another four percent of the places they used to live.

“We knew amphibians were having problems, but we didn’t know how fast they were disappearing. So, this puts some numbers on it, and they’re pretty alarming numbers,” Michael Adams, a research ecologist with USGS in Corvallis, Ore., and the lead author of the study, told The Desert Sun.

It’s not just endangered or threatened species that are declining—it’s all frogs and toads. Researchers looked at species classifications from the International Union for Conservation of Nature’s Red List, the definitive inventory of how threatened animals and plants are, and found that amphibian species of “least concern,” like spring peepers, were still in trouble, disappearing from 2.7 percent of occupied sites each year. Those on the “red list”—endangered, vulnerable or near threatened—did even worse, declining 11.6 percent every year. The findings suggest “amphibian declines may be more widespread and severe than previously realized,” the researchers write.

Worryingly, amphibians disappeared faster from many of the areas designed to preserve them: national parks. In Colorado’s Rocky Mountain National Park, for example, of five documented species of amphibians, one is locally extinct and the other, the boreal toad, has declined dramatically in the last 10 years. And populations of California’s threatened Sierra Nevada yellow-legged and Southern yellow-legged frogs declined 95 to 98 percent in the years leading up to 2008—even in Yosemite National Park.

That frogs and toads are dying even in the best-protected areas suggests the cause of death is not local, but global, Adams said in an interview. Researchers didn’t point to any one cause of the decline, but suggested a number of theories from climate change to habitat degradation to disease.

One disease scientists have their eyes on is chytrid. The fungus has already wiped out 30 amphibian species in Panama, and as National Geographic reports:

“A frogless forest could have reverberations throughout the ecosystem, [Andrew] Crawford, [an evolutionary biologist at the University of the Andes in Bogotá, Colombia], added. For one thing, tadpoles are crucial to stream environments, because they munch on moss and algae along stream beds, taking in protein and other nutrients needed by animals higher up the food chain.”

Chytrid kills frogs and toads by thickening the animal’s skin, making it hard to breathe and disrupting their ability to absorb water and salts. Eventually it causes them to succumb to heart attacks or suffocation.

A landmark 2004 study linked the chytrid fungus to the African clawed frog, which was popular in the pet trade and, until the 1970s, was widely used in hospitals as a pregnancy test: when injected with the urine of a pregnant woman, the frog laid eggs.

Now, a new study reinforces that earlier finding, offering proof that African clawed frogs carrying the fungus have been present in California, where many local species have been on the decline, since the 1970s.

Lead author Vance Vredenburg says the crisis has forced him to think more broadly about amphibian research than in the past. Normally a field ecologist, Vredenburg has been working with immunologists and climate scientists. He’s even culturing bacteria in his lab—quite the departure from netting frogs in glassy alpine lakes. The questions he’s asking are different, too: not just how many frogs are in a given place, but what’s killing them, how they’re dying, how diseases spread, and what to do about it.

“We’ve realized that we can’t just set habitat aside and protect it,” he said, “We have to protect the entire globe.”


Emily Guerin is the assistant online editor at High Country News.
Photos courtesy Vance Vredenburg.