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New USGS research shows that rural areas and farms may be friendlier to frogs and toads than urban areas. Dr. Melinda Knutson, a conservation scientist with the U.S. Geological Survey, said the research on frog and toad populations in two Midwestern states shows that frog and toad abundance and species richness were low in urban areas but near normal in agricultural areas.
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"Despite some risks, Midwestern frog populations seem to coexist with agriculture, the dominant land use in the region," Knutson explained. "Amphibian populations in intensive row-crop agriculture are dependent upon adjacent, less disturbed environments, such as forests, grasslands, emergent wetlands, lakes, and streams. Even small areas of these other cover types may be important in maintaining amphibian populations on the landscape."
Stopping declines in amphibian populations has become a national priority. Before critical habitat can be retained or restored, quality amphibian habitat must be defined. Scientists with the USGS are examining how various landscapes such as wetlands and agricultural areas relate to frog and toad populations. Their research may benefit natural resource managers who have been given the task of promoting healthy and diverse amphibian populations.
The new research also confirmed the role of forests as important amphibian habitat. While wetlands are their primary breeding habitats, many frog and toad species spend part or all of their nonbreeding season in trees, shrubs, or heavy litter, not wetlands, Knutson said. The habitat quality of forests may be just as important as wetlands for these species. The structure of trees, shrubs, and underbrush in a forest creates diverse habitats with many niches. Forests also moderate the temperature and evaporation rate of aquatic habitats adjacent to them, contribute organic matter, and add diversity to the plant and animal community in the area.
In a related study, Knutson and other biologists are investigating the value of constructed farm ponds for native amphibians. Thousands of farm ponds have been constructed in the Midwest through cost-share programs with the U.S. Department of Agriculture. The purpose of these farm ponds is to prevent soil erosion and create wildlife habitat, yet few studies have been conducted to determine how the ponds benefit wildlife such as frogs. One product of Knutson's research will be a guide covering the design, construction, and management of farm ponds for use by contractors, private landowners, and state or federal agencies.
Biologists from the U.S. Geological Survey are helping determine why amphibians are disappearing in the U.S. and across the globe. Research by these scientists and others has identified many deadly virus infections as well as the chytrid fungus as factors in some amphibian die-offs and population declines. Scientists are actively investigating other hypotheses that could help explain these worldwide declines, including global change, contamination from pesticides and other chemicals, increased exposure to ultraviolet radiation due to ozone thinning, and the spread of non-native predators. Many biologists suspect that a combination of factors may be responsible.
These die-offs are of great concern because amphibians are good barometers of significant environmental changes that may go initially undetected by humans. Amphibians, unlike people, breathe at least partly through their skin, making them much more sensitive to environmental insults. The worldwide amphibian declines and deformities could be an early warning that some of our ecosystems -- even seemingly pristine ones -- are seriously out of balance.
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