COS 277-2 - The direct and indirect effects of climate stressors on montane butterflies

Abstract: Climate change is a driver of changes of insect populations in the western United States and it exerts influence along multiple axes, including rising temperature, altered precipitation patterns, and increasingly frequent extreme events. Butterflies, which are important indicator species that play a critical role in pollination and other ecosystem functions, may be sensitive to the effects of climate change, however the interactive nature of these phenomena makes understanding and quantifying various direct and indirect effects on butterflies difficult. Here, we use the most temporally intensive butterfly monitoring dataset in North America, remotely sensed greenness, and high-resolution climate data, to explore hypotheses about the direct and indirect impacts of climate change on butterflies. Specifically, we use Bayesian hierarchical path analysis to quantify the relationships between weather, remotely sensed indicators of vegetation, and butterflies. We show that climate change is having a negative impact on butterfly populations in relatively pristine montane regions. While we find considerable heterogeneity (among species and sites) in the nature and magnitude of weather impacts, the direct impacts of snow melt timing on overwintering butterflies are widespread and potentially important for the future of butterflies experiencing more frequent and extreme disruptions to winter snowfall. These results demonstrate the complexity of climate-driven butterfly declines in montane regions and the importance of considering lagged effects for predicting population responses.