Assessing and mitigating risk to amphibian populations from shifting anthropogenic stressors

Human disturbances to landscapes resulting in habitat degradation and fragmentation frequently drive wildlife population declines by altering demographic rates. A deep understanding of the specific mechanisms that reduce survival of individual life history stages, and the magnitude of the response, is critical to mitigating drivers of decline. I explore how a range of anthropogenic stressors scale to the level of emergent population dynamics using individual level physiological responses and stage-structured demographic models to improve predictions for three conservation challenges: 1) understanding impacts to amphibian populations affected by river hydropower development, 2) forecasting the magnitude and impact of climate change for populations of an amphibian whose range spans across 16o of latitude, and 3) identifying the impact and most effective mitigation strategies for amphibian populations subject to increasing road mortality. I use estimates of individual-level physiological traits to predict how anthropogenic changes in thermal habitat for Coastal tailed-frog (Ascaphus truei) will affect population-level vulnerability from 1) river diversion hydropower dams, and 2) accelerating climate change. I demonstrate that A. truei populations in British Columbia are subject to the equivalent of 50-years of climate warming in rivers where river diversion hydropower dams operate. I find that across the A. truei range, from Northern California to Northern British Columbia, that populations at the southern range boundary have higher immediate vulnerability to climate change. However, faster rates of temperature change in the north, compounded with adaptations to lower temperatures, causes accelerating risk to northern populations. Equally important to forecasting population vulnerability is identifying and evaluating methods to reverse population declines. I use demographic models to elucidate the potential for reducing extinction risk to migrating populations of Northern red- legged frogs (Rana aurora aurora) subject to increasing road mortality by evaluating the effectiveness of two commonly employed mitigation strategies, road-side fencing and wildlife underpasses. I find that the combination of two mitigation structures effectively reverse current population declines for R. aurora, but when I account for increasing vehicle traffic in the future, predict that additional mitigation will be required to prevent population declines and local extinction. In this thesis, I use physiological and demographic models to improve our understanding of the magnitude of current anthropogenic stressors to wild amphibian populations, but also highlight that modern stressors are frequently non-stationary, and present unique challenges to population-scale predictions.
Keywords: River diversion hydropower; climate change; habitat fragmentation; thermal performance; demographic modeling; amphibian decline