Snow avalanches and the impact of climate‐linked extreme events on mountain wildlife population dynamics and resilience

Abstract

Climate is changing rapidly in mountain environments, giving rise to increasing variability in weather, incidence of extremeevents, and alteration of the cryosphere. Natural hazards, such as snow avalanches, and the ecological communities they impactmay be particularly sensitive to such change. While avalanches may impose both ‘good’ and ‘bad’ effects on mountain ecosys-tems, the direct impacts that lead to mortality have particularly important implications for future viability and resilience ofslow-growing alpine wildlife populations. Here, we studied a sentinel species of coastal Alaskan mountain environments—themountain goat (Oreamnos americanus) – using long-term field data from individually marked animals (600 individuals over44 years) in a quantitative modeling framework to understand how avalanches influence demographic processes. Specifically, wedeveloped and parameterized a sex- and age-specific population modeling approach to simulate the effects of avalanche-causedmortality on population growth rate (λ). We examined a range of ecologically relevant scenarios based on empirically observedstates of avalanche-caused mortality. During years when avalanche impacts are severe, populations can experience significantadditive mortality and population declines (up to 15%). Due to low reproductive rates, such impacts can lead to long demographicrecovery times (up to 11 years, or ~1.5 mountain goat generations). Thus, during the course of a typical mountain goat lifetime,significant avalanche-linked perturbations can be expected to occur, suggesting that meaningful demographic signatures of av-alanche impacts are generationally recurrent and routinely imbedded in population histories. From a conservation perspective,such impacts are striking and highlight the utility of employing a quantitative modeling approach to predict possible effects ofavalanches and extreme events more broadly on mountain ungulate population dynamics and viability. Our work explicitlybuilds upon recent findings about the importance of avalanches on mountain-adapted animal populations and has implicationsfor the cultural and ecological communities that depend on them.