Amphibians Information Continued
Copyright Jay Fleming, 2011.
Annual surveys since 2002 have found the same four native amphibian species in Yellowstone: the blotched tiger salamander, boreal chorus frog, boreal toad, and Columbia spotted frog.
In Yellowstone, amphibians depend on limited suitable habitat with shallow, quiet waters needed for egg laying and larval development. Hydrological fluctuations change the extent and location of wetland sites, resulting in considerable year-to-year variation in amphibian reproduction, so longer-term data are needed to identify any significant trends. However, population data collected since 1992 appear to be within the range of natural variability and suggest that these species are resilient to at least short periods of drought. Reports from the 1950s suggest that the boreal toad was more widespread and common then, but it continues to be found at most of the major breeding sites identified since the early 1990s, although at low numbers. After five years of below-normal precipitation, the percentage of visited wetland sites that were suitable for amphibian breeding was 59% in 2007, 96% in 2011, and 75% in 2012.
Disease agents, such as ranavirus and chytrid fungus (Batrachochytrium dentrobatidis), could affect the survival and reproduction of amphibian populations in Yellowstone. Ranavirus has been found in tiger salamanders and Columbia spotted frogs collected from die-offs since 2008. Chytrid fungus does not necessarily cause a fatal infection and usually appears in Columbia spotted frogs and boreal toads following metamorphosis. It has been found in swabs collected from both species in Yellowstone, though the impacts at the population level have not been determined. Several factors, including host susceptibility and environmental conditions, may determine whether an infection is lethal and results in population decline.
Studying amphibians in Yellowstone
Annual measures of amphibian occurrence and wetland suitability allow trends in amphibian populations to be considered in context of the available habitat in Yellowstone. This information is important to understanding how amphibians may be affected by different disturbances. To monitor amphibians in Yellowstone, the Greater Yellowstone Network collects data on the number of wetlands that are occupied by breeding populations of each amphibian species. If occupancy (the proportion of suitable wetlands occupied) decreases, that species has probably declined. To monitor amphibians, researchers randomly select watershed units, known as catchments, from the four main drainage basins of Yellowstone. Field crews search potential habitat within the catchments in June and July to document the presence or absence of amphibians. Researchers study the results to determine occupancy trends and factors that may be driving them.