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Thursday, Jul 19, 2018
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USF scholar leaps ahead on frog losses

TAMPA With frogs, toads and salamanders disappearing from their habitats at an “alarming and rapid rate,” according to a study published last week by the U.S. Geological Survey, a group of local researchers is seeking to slow the decline.
Though disconcerting, the report wasn’t news to Taegan McMahon, a doctoral candidate at the University of South Florida who has been studying amphibian declines for years.
“The USGS work is great, and it doesn’t come as a surprise. We’ve known that amphibian populations are declining, but it’s good to see that their work backs up what we’re seeing,” she said.
“We’re trying to figure out why the populations are declining, but we’re also trying to look at unexplored ways we could possibly do management plans,” she said. “I’m not sure that it’s reversible. I do think if we used appropriate management, we would be able to have a better future for amphibians. I have hope.”
McMahon grew up loving science and loving frogs. As she prepared to defend her doctoral dissertation in biology at USF this week, her mother sent her some childhood photos — one of her pulling creatures out of a pond to examine under a microscope, another of her kissing a toad.
She has been studying parasitology and ecotoxicology, particularly the effect of pesticides on amphibians. Her discovery that crayfish could be the vehicle that carries the chytrid fungus that is so devastating to amphibians landed her in the Proceedings of the National Academy of Sciences and in National Geographic News.
That would be one way to attack the problem, she said: manage the spread of crayfish, and you might manage the fungus.
But the chytrid fungus is only one culprit scientists think are decimating the amphibians. The fungus isn’t found in Florida, but here and elsewhere, the species are struggling against habitat loss, pollution, agricultural runoff and parasites.
The USGS study looked at nine years of population data in 34 ponds, lakes and other habitats spanning 48 species. It did not look at the causes of the declines but sounded an alarm.
“Amphibians have been a constant presence in our planet’s ponds, streams, lakes and rivers for 350 million years or so, surviving countless changes that caused many other groups of animals to go extinct,” said USGS director Suzette Kimball. “This is why the findings of this study are so noteworthy; they demonstrate that the pressures amphibians now face exceed the ability of many of these survivors to cope.”
One of the survey’s surprising conclusions was that declines were occurring even in conservation lands such as national parks and wildlife refuges.
“There have been people documenting amphibian declines for at least a few decades now,” said Jason Rohr, a professor of ecology at USF who has worked and published with McMahon. “A lot of the emphasis has been more on the tropical species and certain parts of the United States. This survey might suggest that it’s a more widespread problem than was previously thought.”
Why should the layperson fret over dwindling populations of creatures that few of us ever encounter, or want to encounter?
“Biodiversity is extremely important to the health of the ecosystem,” McMahon said. “In order to have a healthy environment in Florida, we have to have a really wide variety of organisms, and frogs are an organism that is really important.”
Further, she said, they serve as bioindicators.
“When the frog populations start to decline, we see there must be something wrong in the environment. Frogs are the first one to go: the canary-in-the-coal-mine concept. If they’re going down, other things are going to start to decline as well.”

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