Compounding effects of climate change reduce population viability of a montane amphibian

Abstract

Anthropogenic climate change presents challenges and opportunities to the growth, reproduction, and survival of individuals throughout their life cycles. Demographic compensation among life‐history stages has the potential to buffer populations from decline, but alternatively, compounding negative effects can lead to accelerated population decline and extinction. In montane ecosystems of the U.S. Pacific Northwest, increasing temperatures are resulting in a transition from snow‐dominated to rain‐dominated precipitation events, reducing snowpack. For ectotherms such as amphibians, warmer winters can reduce the frequency of critical minimum temperatures and increase the length of summer growing seasons, benefiting post‐metamorphic stages, but may also increase metabolic costs during winter months, which could decrease survival. Lower snowpack levels also result in wetlands that dry sooner or more frequently in the summer, increasing larval desiccation risk. To evaluate how these challenges and opportunities compound within a species’ life history, we collected demographic data on Cascades frog (Rana cascadae) in Olympic National Park in Washington state to parameterize stage‐based stochastic matrix population models under current and future (A1B, 2040s, and 2080s) environmental conditions. We estimated the proportion of reproductive effort lost each year due to drying using watershed‐specific hydrologic models, and coupled this with an analysis that relates 15 yr of R. cascadae abundance data with a suite of climate variables. We estimated the current population growth (λs) to be 0.97 (95% CI 0.84–1.13), but predict that λs will decline under continued climate warming, resulting in a 62% chance of extinction by the 2080s because of compounding negative effects on early and late life history stages. By the 2080s, our models predict that larval mortality will increase by 17% as a result of increased pond drying, and adult survival will decrease by 7% as winter length and summer precipitation continue to decrease. We find that reduced larval survival drives initial declines in the 2040s, but further declines in the 2080s are compounded by decreases in adult survival. Our results demonstrate the need to understand the potential for compounding or compensatory effects within different life history stages to exacerbate or buffer the effects of climate change on population growth rates through time.

Water loss and temperature interact to compound amphibian vulnerability to climate change

“…Potentially, individuals could shift their active seasons earlier (Benard, 2015) to avoid the high temperatures and rates of EWL in July and August; however, individuals would still require behavioural strategies for the duration of the snow‐free season prior to October. While restriction acts at the level of the individual, these seasonal changes are expected to have population‐level consequences, including negative population growth rates and local extinction (Kissel, Palen, Ryan, & Adams, 2019).…”

Elevation alters outcome of competition between resident and range‐shifting species

“…picturatus population persistence at subalpine and montane habitats requires examining long-term demographic data or modeling populations based on body mass-fecundity relationships, survival rates, and estimates of immigration and emigration of adults across elevation (e.g., Kissel et al, 2019). More broadly, research that determines the sensitivity of population dynamics to changes in the suite TA B L E 3 Model coefficients from linear mixed-effects models examining the effect of competition, elevation, and their interaction on larval Limnephilus externus mass and adult Limnephilus picturatus mass of demographic parameters among elevations should be a fruitful in understanding species ranges and range shifts, especially for animals with complex life histories where different developmental stages and life-history parameters are often affected differently by environmental variables (Kingsolver et al, 2011).…”

Hydrothermal physiology and climate vulnerability in amphibians

“…Further, the warming and drying of aquatic larval habitats can result in smaller post-metamorphic juveniles in amphibians [58], and these individuals will then have to navigate a drier terrestrial environment with the added disadvantage of being smaller [59]. If conditions are sufficiently harsh in the terrestrial landscape, then this could result in a collapse of recruitment in addition to the persistent challenges a warmer, drier climate will pose for adult demographic fitness [13]. We may therefore expect climate warming to exert dual pressures of developmental shrinking and accelerated dehydration that could magnify climate-induced population declines and losses into the future.…”