COS 280-5 - Pollinator group, body size and sex drive taxonomic and phylogenetic patterns of pollen transport in a diverse co-flowering community

Abstract: Pollinators play an important ecological role due their ability to carry and disperse pollen among flowers and ensure plant reproductive success. Patterns of pollen transport on pollinators bodies however are also key for elucidating community level plant–plant interactions via heterospecific pollen transfer and the ecological function of pollinators based on their use of floral resources (e.g., niche breadth), both of which can help mediate community assembly. Pollinators vary in their morphology, behavior and life history, which can lead to differences in patterns of pollen transfer among and within pollinator groups (e.g., bees and flies), and hence in their functional role within a community. Furthermore, the importance of intrinsic pollen load characteristics such as the phylogenetical and phenological (flowering times) diversity of pollen loads and how these may vary between insect groups has been little understood. Here, we evaluate whether pollinator group, body size, and sex influence the size and richness of pollen loads as well as phylogenetical and phenological distances within pollen loads. For this, we collected a total of 782 flower-visiting bees and flies at the serpentine seep plant communities in northern California in 2021. Pollen loads were sampled by swabbing insects, except scopae and corbiculae, with fuchsin jelly. Pollen grains were counted and identified in a microscope at 40x. We determined the morphospecies (~100 spp.), sex, and body size (intertegular distance) of each insect specimen. Insects were divided into five categories: bumble bees, honeybees, megachilid bees, other bees and flies. We found differences in pollen load size and richness between pollinator groups. Bumble bees carried the most diverse pollen loads as honey bees, and their size was larger than megachilid bees and flies, which carried the smallest loads. Female bees transported more pollen grains than males, but not more pollen species. Body size was positively related to both pollen load size and richness, but did not affect phylogenetical diversity of pollen loads. Phylogenetic diversity in pollen loads however was higher in megachilid bees than flies and for males than females. Phenological distances of pollen loads was not different among pollinator groups and was not influenced by pollinator size or sex. Our results suggest that differences in the ecological role within and among pollinators groups based on their taxonomic and phylogenetic niche breadth may have the potential to mediate plant-plant interactions and ultimately plant community assembly.