Many alpine landscapes of Western North America are peppered with hundreds to thousands of lakes and small wetlands that are historically fishless, and as such the top predators are often omnivorous macroinvertebrates and amphibians. These systems exhibit tremendous site-to-site variation in everything from temperature, hydroperiod, snow cover, water color (DOM), pH, and the geophysical template on which they sit. Over the past century, many of these sites have been introduced with self-sustaining populations of non-native trout, which virtually eliminate many of the native taxa including amphibians. The spatial dynamics of modern amphibian populations that use these landscapes for reproduction represent a critical limitation in our ability to determine both the status of current populations and predictions of the potential effects of additional stressors (climate change, emerging diseases, etc.). In 2000 the Sol Duc watershed of the Olympic National Park where we have done extensive work was designated as a sentinel site for the Amphibian Research and Monitoring Initiative (ARMI). As part of an ongoing project funded by ARMI to M.J. Adams (USGS), we have been following a population of Cascades frogs, Rana cascadae, to estimate population size and determine the levels of site fidelity, frequency of breeding, body condition, and survival of individuals within the population. At the most basic level, this provides a rigorous annual estimate of population size with which to assess population status through time, data which are otherwise exceedingly scarce. We are also answering a range of questions relevant to amphibian conservation and metapopulation dynamics. What is the extent of information required to make appropriate conservation and management decisions about amphibian populations? What rules do we use to prioritize the conservation of a sub-set of ponds to ensure population persistence under a variety of current and future disturbance and climatic regimes? Does our ability to accurately characterize population dynamics change as a function of the extent of our knowledge of the spatial connectivity between sub-populations (ponds) and the degree of site fidelity among individual species? Can we prioritize sites for fish removal to ensure amphibian persistence under future climate scenarios?
We are key partners in a large collaboration with hydroclimatologists (A. Hamlet, S.Y. Lee), climate adaptation specialists (L. Hansen), and biologists from government and the academy (M. Adams, R. Knapp) where we are using extensive inventory data collected for montane amphibians in the Pacific Northwest to test theories of how synergies between anthropogenic stressors may exceed the resilience capacity of ecosystems and result in a rapid loss of biodiversity and function. The Pacific Northwest (PNW) is experiencing the largest snowpack decline in the western US, resulting in shifts in precipitation from snow to rain, increased frequency of summer droughts, and reductions in wetland hydroperiods. The presence of non-native trout in most large montane lakes of the PNW restricts current amphibian distributions to primarily small permanent wetlands not occupied by exotic trout—sites that may be disproportionately vulnerable to future drying. The displacement of amphibians by exotic trout may have eroded the historic resilience of these ecosystems, and pushed them towards an unanticipated tipping point. Using novel hydrologic models (A. Hamlet, S.Y. Lee), remote sensing tools to identify wetlands (M. Halabisky), and amphibian occupancy models, we are evaluating the potential for dramatic changes to available amphibian habitat in the future from the synergy of sequential impacts; displacement by trout followed by climate-induced wetland drying. Such sequential synergistic impacts have thus far been poorly studied in any system, yet may represent an under appreciated class of ecological mechanisms leading to catastrophic shifts in ecosystems. This case study may also represent one of the few opportunities to prevent the rapid loss of biodiversity with targeted restoration activities (removal of trout from the most vulnerable landscapes, or those with the largest capacity for resilience), and we are working closely with many US State and Federal agencies to implement this work in the coming years.