Graduation Date

Spring 2020

Document Type



Master of Science degree with a major in Natural Resources, option Wildlife

Committee Chair Name

Brian Hudgens

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Daniel Barton

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

John Reiss

Third Committee Member Affiliation

HSU Faculty or Staff

Subject Categories



As human activities reach every corner of the globe, climate change, invasive species, habitat destruction, and other stressors causing species’ declines no longer act alone. Climate change has the potential to exacerbate (or mitigate) other stressors (e.g. invasive species or pathogens) affecting amphibian populations. I assessed the combined effects of increased pond drying rates (potential impact of climate change), invasive bullfrogs (Lithobates catesbeianus) presence, and food availability on northern red-legged frog (Rana aurora) survival and body size after metamorphosis by rearing tadpoles under incrementally shortened hydroperiods with and without the presence of invasive bullfrog tadpoles in low and high food environments. To explore the underlying mechanisms driving the impact of bullfrogs on R. aurora tadpoles, I had two treatments where bullfrog tadpoles were either separated by a permeable barrier (behavioral cue) or free to move about the tanks (direct competition/predation). To validate the captive experiment, I examined the influence of hydroperiod length on R. aurora survival, development, and growth in a field-based mesocosm experiment. I found hydroperiod to have a threshold effect on survival through metamorphosis in the captive experiment. Once the hydroperiod threshold was met in both the captive and field study, I found no benefit of longer hydroperiods on survival through metamorphosis. Drying rate influenced R. aurora developmental rates, but the effects were dependent on life stage and time of season in the field study. Size at metamorphosis was synergistically affected by bullfrog presence and food availability in the captive experiment. Tadpoles emerged as smaller metamorphs when exposed to bullfrogs in a low food environment. In the field experiment, size at metamorphosis was positively affected by longer hydroperiod and later emergence date. Understanding how multiple stressors impact larval growth and survival is an important component for managing and potentially mitigating the interactive effects of climate change and invasive species for amphibian conservation.

Citation Style



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