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

Climate change disrupts ecological systems by shifting species distributions and altering phenological patterns, significantly affecting interspecific interactions like Batesian mimicry. Effective mimicry relies on the spatial and temporal overlap between mimics and their models to deter predators. This idea has persisted despite emerging data that challenges it. To assess phenological position and flight season changes, we extracted flight season data for model bumblebee species and mimicking hoverflies for the Scandinavian peninsula, spanning a little over century-and-a-half. We estimated shifts in the annual mean flight season and the phenological order of emergence in our Batesian system while accounting for yearly survey variations. We found compelling evidence of a temporal shift in flight season dynamics in the Batesian system. Mimics historically flew significantly earlier than models, but in more recent years, there has been a pronounced trend towards mimics flying later than models. This temporal decoupling highlights potential impacts on mimicry effectiveness, as mismatches with peak model activity periods could increase the predation risk for mimics. The shift from mimics emerging earlier to models flying earlier is particularly concerning, underscoring the fitness consequences of climate-driven changes on ecological interactions.  

Methods
Flight season data (citizen-science observations and museum specimens) of model bumblebees and mimic hoverflies was extracted from Norwegian Artsdatabanken (https://www.artsdatabanken.no) and Swedish Artportalen (https://artportalen.se/). The data was cleared off records lacking valid species names and duplicate entries; with start and end dates exceeding one month were deemed invalid and excluded from further analysis.