Tracking a Toad's Traces
Unnoticed by many people, amphibians rank among the most threatened animals on the planet, with 30 percent of species already in danger of disappearing. Frogs, toads, salamanders, and newts are being decimated worldwide by habitat loss, invasive species, and the spread of diseases like chytrid fungus.
Amphibian population figures are not always easy to come by, but researchers have a surprisingly powerful resource in the specimen collections of natural history museums. Behind the scenes, researchers use museum collections to track and preserve wildlife from extinction.
Mason Ryan, an amphibian researcher at the University of New Mexico, is a strong advocate of using museum collections to understand how species adapt to changes in the environment. Ryan is part of a team funded by the New Mexico Department of Game & Fish to study amphibian declines in the state, like the native Chiricahua Leopard Frog, federally listed as threatened in 2002.
One species of special concern to them now is the Arizona Toad (Anaxyrus microscaphus), native to the Gila region. This toad has been seen active in early spring, when ice can cover streams, at temperatures as low as 30 degrees. The toad has been heard calling during daylight hours—rare in North American toads—and can consume such noxious insects as blister beetles, spiders, and centipedes. It shares the same geographic range as the Chiricahua Leopard Frog, though it occurs in different types of habitat.
Ryan and his colleagues Ian Latella, Tom Giermakowski, and Howard Snell have been using natural history museum records as the basis for their study of the Arizona Toad. “Because of the work done by researchers in New Mexico between the 1950s and 1990s, we were able to determine the specific localities where the toads used to be found,” Ryan explains. For three years the researchers re-checked those historic locations, and found the toad had disappeared from almost 60 percent of its former range.
“Unfortunately, there isn’t data on population sizes at all the sites. But only two sites out of the 31 occupied sites that we looked at had high density,” Ryan says. The data strongly suggest the Arizona Toad is in trouble, and Ryan suspects the primary cause is loss of breeding habitat from long-term drying trends. The toad’s life cycle appears to be disrupted by habitat loss and drought caused by forest fires and climate change.
Museum records on the Woodhouse’s Toad offer additional clues. This toad, native to New Mexico and highly tolerant of human-altered environments, will mate with many other toad species—including the Arizona Toad—giving birth to hybrids that gradually replace their genetically pure forebears. Museum collections documenting the spread of Woodhouse’s Toads in areas of Arizona with altered stream flows led Ryan’s team to hypothesize that Arizona Toads in the Gila were being protected by an absence of local water-diversion projects.
“Any water diversion, anything that slows a stream and creates a pool behind it, that’s an ideal habitat for the Woodhouse’s,” Ryan said. “We looked at all our specimens to see if the toads had any characteristics of the hybrids, and none showed any evidence of hybridization. That fits with our hypothesis, because the Gila doesn’t have any impoundments.”
In late June, the U.S. Fish & Wildlife Service announced that, in response to a petition by the Center for Biological Diversity, it would consider listing the Arizona Toad as an endangered species. The agency is collecting scientific information about the toad, specifically about the threat of Woodhouse’s Toad hybridization.
Meanwhile, Ryan and his team have come up with some ideas to help the Arizona Toad hang on, through “continued monitoring at key sites, and moving eggs or tadpoles that are threatened with desiccation.” Habitat surveys can also help keep the Arizona Toad from disappearing from New Mexico.
“Our work would not have been possible without the specimens or data we were able to obtain from museums,” Ryan says. Efforts made by museum field collectors in the past allow us to document long-term changes in native wildlife and how species respond to environmental change, suggesting ways to help save endangered species before it’s too late.
