From lagging to leading: Increased phenological asynchrony in a Batesian mimicry complex

Climate change can alter species interactions by shifting phenology and species distributions. Batesian mimicry is one such interaction in which mimic protection is often assumed to depend on temporal and spatial overlap with defended models, although recent studies suggest strict synchrony may not always be required. To examine long-term mimic-model phenological dynamics, we compiled flight season data for bumblebee models and their hoverfly mimics across the Scandinavian Peninsula spanning a little over a century and a half. We estimated shifts in mean flight season and the relative order of emergence while accounting for variation in sampling effort among years. The flight periods of several bumblebee models advanced over time, whereas the hoverfly mimic remained largely unchanged. We found a marked shift in seasonal flight time within our bumblebee-hoverfly mimicry system. Historically, mimics flew earlier than their bumblebee models, but in recent decades the pattern has reversed, with models emerging earlier than mimics. This shift reduces temporal overlap between mimics and peak model activity and may alter the conditions under which mimicry provides protection.