Temperature influences pollinators' choice of floral partners independently of community composition

Climate change can impact species interactions by changing the spatial and/or temporal overlap of interaction partners, but interspecific interactions can also vary when partners remain co-located in space and time. Understanding the effects of climate-driven environmental variation, such as rising temperatures, is particularly important for interactions that underlie key ecosystem functions like pollination. However, very little is known about how temperature variation may impact plant-pollinator interaction patterns in the absence of shifts in species presence or abundance, in part because environmental variation across multiple days or sites is often confounded with changing community composition. In this study, we examined the effects of temperature variation on pollinators' choice of floral partners within near-static ecological communities by sampling interactions at multiple temperatures within individual days-a method that allowed us to disentangle the effects of temperature variation and species turnover on patterns of plant-pollinator interactions. The substantial temperature variation both within and across days in each growing season also enabled us to largely disentangle temperature variation from time-of-day effects. With this sampling protocol, we show that temperature can influence pollinator floral choice independently of changes in species composition. We found differences in the choice of floral resources across pollinator taxa as temperature varied during individual days and further found that bumble bees, but not sweat bees, exhibited this pattern when analyzed independently. We also confirmed that our observed trends were not driven by variation in the number of interactions recorded, the relative abundance of pollinators, or in the overall attractiveness of flowers at different temperatures. We propose that thermal niche partitioning in this system could be driven by physiological and behavioral factors including energetics and competition for specific floral resources at different temperatures. These insights into thermal variation in pollinators' floral choice contribute to wider understanding of the fine-scale mechanisms through which climate change may impact ecological networks, community resilience, and ecosystem functioning.