Amphibian communities and climate change: where ecological processes meet evolutionary interactions

Graduation date:2017Forecasts of the impacts of climate change have traditionally focused on individual species and their phenotypes, phenology, or distribution. However, shifts in species distributions and the resulting reorganization of community composition represent an important violation to the assumption of species acting in isolation. Whereas species may respond individualistically to climate change, the manifestations of their responses will be largely influenced by interactions with other organisms. Tractably dealing with complex interaction networks in the face of climate change will require an understanding of community dynamics and the degree to which biotic interactions influence species' behavior, physiology, and survival – and ultimately their footprint on the landscape. \ud To improve our understanding of community-level responses to climate change, I explored amphibian response strategies from both a population- and community-level perspective and provided a critical evaluation of one of the primary methods for incorporating biotic interactions into predictive species distribution models. In Chapter 2, I evaluated amphibian species’ physiological constraints and the potential consequences of phenotypic plasticity as a first step to understanding their sensitivity, and ultimately, adaptive capacity to climate change. I experimentally quantified phenotypic plasticity in larval growth and development in three high elevation Anuran species (Anaxyrus boreas, Pseudacris regilla, and Rana cascadae) in response to projected climate warming scenarios for the Cascade Mountain Range. Warming initiated faster weight gain and accelerated larval growth rates in each of the species. However, any effort to achieve optimum body size (in both length and weight), while maintaining the necessary developmental trajectory under heat stress, was relatively unsuccessful. \ud In Chapter 3, I tested the response strategies of the same three Anuran species to a different climate stressors, hydroperiod reduction (i.e. drought), and included the additional stress of interspecific competition. I found that competition exacerbated the effects of drying on competitively inferior species (Anaxyrus boreas and Pseudacris regilla) and that, in general, species responses were largely context-dependent. My results emphasize the importance of biotic interactions in predictions of species response to climate change. \ud In Chapter 4, I provide a critical evaluation of standard methods for incorporating biotic interactions into predictive species distribution models. Most methods utilize observational data via species co-occurrences on the landscape to infer the role of biotic interactions in structuring species distributions. Results from a series of tests using two long-term amphibian co-occurrence datasets from Mt. Rainier National Park (Washington) and Mt. Hood (Oregon) show that the current best available methods are largely disconnected from community ecology theory and have yet to reconcile the complex dynamics within trophically-structured communities.\ud My research aims to fill a critical knowledge gap in the connection between community dynamics and biogeography, with significant implications for conservation and management of a severely threatened taxonomic group. I highlight the significant challenges of estimating species response to climate change across multiple levels of taxonomic organization and spatio-temporal scales