Debra A. Patla

Estimating Occupancy in Large Landscapes: Evaluation of Amphibian Monitoring in the Greater Yellowstone Ecosystem

Monitoring of natural resources is crucial to ecosystem conservation, and yet it can pose many challenges. Annual surveys for amphibian breeding occupancy were conducted in Yellowstone and Grand Teton National Parks over a 4-year period (2006–2009) at two scales: catchments (portions of watersheds) and individual wetland sites. Catchments were selected in a stratified random sample with habitat quality and ease of access serving as strata. All known wetland sites with suitable habitat were surveyed within selected catchments. Changes in breeding occurrence of tiger salamanders, boreal chorus frogs, and Columbia-spotted frogs were assessed using multi-season occupancy estimation. Numerous a priori models were considered within an information theoretic framework including those with catchment and site-level covariates. Habitat quality was the most important predictor of occupancy. Boreal chorus frogs demonstrated the greatest increase in breeding occupancy at the catchment level. Larger changes for all 3 species were detected at the finer site-level scale. Connectivity of sites explained occupancy rates more than other covariates, and may improve understanding of the dynamic processes occurring among wetlands within this ecosystem. Our results suggest monitoring occupancy at two spatial scales within large study areas is feasible and informative.

Roles of Patch Characteristics, Drought Frequency, and Restoration in Long‐Term Trends of a Widespread Amphibian

Despite the high profile of amphibian declines and the increasing threat of drought and fragmentation to aquatic ecosystems, few studies have examined long-term rates of change for a single species across a large geographic area. We analyzed growth in annual egg-mass counts of the Columbia spotted frog (Rana luteiventris) across the northwestern United States, an area encompassing 3 genetic clades. On the basis of data collected by multiple partners from 98 water bodies between 1991 and 2011, we used state-space and linear-regression models to measure effects of patch characteristics, frequency of summer drought, and wetland restoration on population growth. Abundance increased in the 2 clades with greatest decline history, but declined where populations are considered most secure. Population growth was negatively associated with temporary hydroperiods and landscape modification (measured by the human footprint index), but was similar in modified and natural water bodies. The effect of drought was mediated by the size of the water body: populations in large water bodies maintained positive growth despite drought, whereas drought magnified declines in small water bodies. Rapid growth in restored wetlands in areas of historical population declines provided strong evidence of successful management. Our results highlight the importance of maintaining large areas of habitat and underscore the greater vulnerability of small areas of habitat to environmental stochasticity. Similar long-term growth rates in modified and natural water bodies and rapid, positive responses to restoration suggest pond construction and other forms of management can effectively increase population growth. These tools are likely to become increasingly important to mitigate effects of increased drought expected from global climate change. Papeles de las Características del Fragmento, Frecuencia de Sequía y Restauración en las Tendencias a Largo Plazo de un Anfibio Ampliamente Distribuido.

Influence of Water Conductivity on Amphibian Occupancy in the Greater Yellowstone Ecosystem

ABSTRACT. Investigation of amphibian occupancy at potential breeding sites can provide information about the distribution and relative abundance of species, as well as insights into habitat relationships across large areas such as national parks. Based on previous research in the Greater Yellowstone Ecosystem (GYE), we hypothesized that the probability of amphibian occupancy increases with water conductivity. We conducted amphibian surveys with habitat measurements at 235 wetland sites in the GYE in 2002, thereby locating breeding populations of boreal toads (Anaxyrus boreas), boreal chorus frogs (Pseudacris maculata), Columbia spotted frogs (Lithobates luteiventris), and barred tiger salamanders (Ambystoma mavortium). Repeat surveys provided detection probabilities, which allowed for unbiased estimates of occupancy. The boreal chorus frog was the most common amphibian in the GYE, with breeding populations occupying approximately 48% of the sites, followed by Columbia spotted frog (35%), barred tiger salamander (14%), and boreal toad (13%). Occupancy corrected for detection probability averaged 36% higher (range 27%–50%) than naive estimates of occupancy. Detection rates ranged from 0.65 to 0.78 for the 4 species. Modeling of habitat covariates indicated that higher conductivity was positively associated with toad occupancy but negatively associated with chorus frog occupancy; Columbia spotted frog and barred tiger salamander occupancy was little influenced by water conductivity. Fish presence had a negative effect on occupancy of barred tiger salamanders and boreal chorus frogs. These results may help managers in the GYE manage and conserve important breeding habitat for amphibians, particularly if longterm monitoring efforts indicate declines in amphibian populations.