Amphibian populations are rapidly declining worldwide. Although individual factors may have large local influences, worldwide declines are attributed to interacting global stressors including rising temperatures and environmental pollutants. Globally, water temperatures closely track rising air temperatures and increase the metabolic rates of aquatic ectotherms, changing the rates of uptake, biotransformation, and excretion of contaminants, such as metals. To test how interactions of multiple, chronic stressors affect amphibian growth, I exposed Cope's gray treefrogs (Hyla chrysoscelis) in an outdoor mesocosm facility to three temperature regimes (ambient, ambient +1.5 oC, ambient +2.5 oC) in filtered lake water amended with mixtures of cadmium, copper, and lead ranging from 3.7 to 26.7 risk quotients (relative to the chronic concentration criteria protective of freshwater organisms). Temperature shifts and sublethal metals concentrations significantly affected the energetics of tadpoles as assessed by non-parametric and parametric analyses. Regression analyses indicated no significant relationship between temperature and time to forelimb emergence at the three lowest metals concentrations, but the relationship was parabolic at the three highest concentrations, indicating a differential effect of temperature across a gradient of water quality. The concept that tadpoles increase developmental rates to escape unfavorable aquatic conditions was supported at each temperature by shortened time to forelimb emergence (Gosner Stage 42) at the second highest metals concentration. This response, however, was overwhelmed by the energetic costs associated with the highest concentration and the highest temperature. Moreover, these parabolic relationships match predictions based on species specific thermal windows and pejus temperatures. My findings indicate that global warming may affect contaminated waters to a greater extent than pristine aquatic ecosystems, and that the primary effect may be diminished pejus and critical thermal maximum temperatures, and a narrowing of the species' thermal window.

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Amphibians and aquatic invertebrates have complex life histories that link aquatic and terrestrial food webs. It has been suggested that amphibian reproduction is an important source of carbon to some aquatic systems. This process of energy flow may be shaped by shifts in habitat selection in response to predators. We hypothesized that predators decrease colonization and oviposition of prey, reducing active inputs. Thus predation risk is expected to shift the relative amounts of active and passive subsidies. We manipulated the presence of fish predators in aquatic mesocosms. Results suggest hylid treefrog eggs and hydrophilid beetles were less abundant in predator treatments. This difference in oviposition and colonization translated into small reductions in calories and ash free dry mass of active inputs. However, passive allochthonous inputs were more than double active amounts and variable, therefore relative amounts of active and passive inputs did not differ across the levels of predation risk.

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Fire may alter both aquatic and terrestrial habitat used by all amphibian life stages, yet, our knowledge of its effects on amphibians is primarily limited to adult responses. I present an integrated approach to test the response of Cope’s Gray Treefrog (Hyla chrysoscelis) to fire by examining responses in tadpole performance and survivorship, adult abundance, and oviposition. Tadpoles raised with burned leaf litter had similar survival, but total mass and total length were 440% and 170% greater, respectively, for tadpoles raised in unburned litter. I assessed terrestrial and aquatic oviposition cues by embedding burned and unburned litter treatments within burned and unburned terrestrial plots. Oviposition was an order of magnitude higher in unburned plots, regardless of the litter treatment. This difference was not statistically significant or driven by adult abundance. My results indicate the need to explore the dynamic effects forest management practices can have on amphibians across life stages.

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