Environment & Science

California's amphibians threatened by climate change, urbanization and more

Above, one of a handful of juvenile California red-legged frogs who have survived their first year in the Santa Monica Mountains, the first of the species to live in the Santa Monica Mountains since the 1970s. Biologists hope the juveniles will survive into adulthood and will begin breeding in the spring of 2016.
Above, one of a handful of juvenile California red-legged frogs who have survived their first year in the Santa Monica Mountains, the first of the species to live in the Santa Monica Mountains since the 1970s. Biologists hope the juveniles will survive into adulthood and will begin breeding in the spring of 2016.
National Park Service

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It ain’t easy being green… or yellow, or red, or any of the other colors you see on Southern California amphibians, according to new research from the U.S. Geological Survey, which found creatures like frogs, salamanders and toads are on a steady decline.

Across the country, the number of amphibians is dropping by about 4 percent every year, according to the study which was published in the open-access journal Scientific Reports.

That number is likely higher in Southern California, where USGS research ecologist Robert Fisher says roughly half of all amphibians are threatened by one factor or another.

"We’ve got climate we’ve got drought, we’ve got urbanization... we’ve got a million different things," Fisher commented.

For instance, dammed rivers and diverted water flows have taken away many of the niche habitats of certain toads, while populations of other species are suffering from prolonged drought — something researchers expect more of thanks to climate change.

Among the local species in trouble: Arroyo toads, California red-legged frogs, the California tiger salamander, mountain yellow-legged frogs, western spadefoot toads and desert slender salamanders.

Fisher says these amphibians are important ecological bellwethers since they live on land and water.

"You need both of those systems together for them to be functional," Fisher said.

Across the U.S., four main factors are driving these population die-offs: habitat loss from human influence, pesticide use, climate change and disease — particularly a chytrid fungus called Batrachochytrium dendrobatidis.

You can see how each of those four threats are spread across the country in the graphic below:

Values are summarized and normalized at the HUC sub-basin scale, using ArcGIS (ver. 10.2. Redlands, CA: Environmental Systems Research Institute). (a) Human influence index. (b) Suitability for Batrachochytrium dendrobatidis. (c) Average annual pesticide application. (a–c) Red indicates higher than average threat intensity while green is lower than average. Locations of amphibian community data indicated with circles; symbols indicate region groupings (see Table 1; circles = Northeast, diamonds = Southeast, plus = Midwest, triangles = West coast, squares = Rocky Mountains). (d) The mean difference in the 30-year normal from the 2001–11 annual average precipitation; blue indicates wetter sub-basins with above average difference in precipitation while red indicates drier sub-basins.
Values are summarized and normalized at the HUC sub-basin scale, using ArcGIS (ver. 10.2. Redlands, CA: Environmental Systems Research Institute). (a) Human influence index. (b) Suitability for Batrachochytrium dendrobatidis. (c) Average annual pesticide application. (a–c) Red indicates higher than average threat intensity while green is lower than average. Locations of amphibian community data indicated with circles; symbols indicate region groupings (see Table 1; circles = Northeast, diamonds = Southeast, plus = Midwest, triangles = West coast, squares = Rocky Mountains). (d) The mean difference in the 30-year normal from the 2001–11 annual average precipitation; blue indicates wetter sub-basins with above average difference in precipitation while red indicates drier sub-basins.
USGS

If this trend continues, researchers estimate that these species will disappear from half of the habitats they occupy in about 20 years.

Fisher says that, since there are so many threats facing amphibians, conservationists will need to take a tailor-made strategy for helping each species in their individual locations.

The next step is to use research like this to come up with management plans to do just that, he said.