Applying physiologically-guided modeling to predict heat wave risk to California pollinators

An increase in exposure to extreme heat threatens to undermine critical ecological processes of which insect-mediated pollination is one key example. The extreme temperatures associated with heat waves are poised to impact pollinator activity rates and thus pollination services, but the direction and magnitude of anticipated changes as well as where, when, and for what crops risk is likely remains unknown leaving crops vulnerable to significant loss. Current risk assessment frameworks, largely based on climate niche models, struggle to accurately predict the impact of heat waves because contemporary temperatures regularly exceed the bounds of historical data, forcing extrapolation. We use a physiologically-guided approach that leverages continuous activity data from remote cameras to model pollinator thermal activity/performance curves and use these models along with climate projections to estimate the change in pollinator activity across California given anticipated warming. We combine these model projections with spatially-explicit crop locations to quantify the risk posed to specific pollinator-dependent crops and their primary bee taxa visitors. Our results show a wide range of thermal tolerances across bee taxa and resultant shift in predicted pollinator activity. We predict a substantial (5-25%) decrease in pollinator activity in the major crop production regions of California over the next 75 years, notably across the southern Central Valley as temperatures exceed species' thermal tolerances. Our work provides a first-step in identifying regions of risk that can be targeted with additional research and climate resilience efforts in order to ensure a stable supply of insect pollinators in a rapidly changing world.