Amphibians and Disease: Implications for Conservation in the Greater Yellowstone Ecosystem

The decline of amphibian populations is a worldwide phenomenon that has received increasing attention since about 1990. In 2004, the World Conservation Union’s global amphibian assessment concluded that 48% of the world’s 5,743 described amphibian species were in decline, with 32% considered threatened (Stuart et al. 2004). Amphibian declines are a significant issue in the western United States, where all native species of frogs in the genus Rana and many toads in the genus Bufo are at risk, particularly those that inhabit mountainous areas (Corn 2003a,b; Bradford 2005). As is true for most of the cold and dry Rocky Mountains, relatively few amphibian species are native to the Greater Yellowstone Ecosystem (GYE; Table 1). One of the five native species, the northern leopard frog (Rana pipiens), may have been extirpated. Except for a photograph of leopard frogs taken near Flagg Ranch in 1995 and an occasional unsubstantiated report, this species has not been observed during recent surveys. The remaining four species are distributed throughout the GYE, and their ranges do not appear to have retreated from historical coverage of the landscape. However, some or all of these species are declining or have declined in some portions of the GYE. Although we lack the historical data to judge whether the current percentages of potential breeding sites occupied represent declines for most species, it is likely that boreal toads have declined to some extent in the GYE. This species has declined severely in the southern Rocky Mountains (Colorado, northern New Mexico, and southeast Wyoming), and occupancy of 5% of potential breeding sites (based on sampling at selected water catchments) in the GYE is lower than the 7–15% occupancy observed in similar surveys in Glacier National Park