Floral volatiles structure plant-pollinator interactions in a diverse community across the growing season

While the importance of floral odours for pollinator attraction relative to visual cues is increasingly appreciated, how they structure community-level plant-pollinator interactions is poorly understood. Elucidating the functional roles of flowering plant species with respect to their floral volatile organic compounds (VOCs) and how those roles vary over the growing season is an initial step towards understanding the contribution of floral VOCs to plant-pollinator interaction structure. We sampled the floral VOCs, phenologies and bee visitors of naturally growing plants in a montane meadow in the Northern Rocky Mountains of USA in order to acquire a base understanding of how floral VOCs and other plant traits may structure plant-pollinator interactions across the growing season. We expected forb species with floral VOCs that were original (far from the community mean) and unique (far from the nearest neighbour) would have few pollinating partners (i.e. specialists), while forbs with non-original or highly variable floral VOCs would form the generalist core of interactors, thereby contributing to network nestedness (specialists interacting with nested subsets of generalists). Network modularity (patterns of distinct, highly connected subnetworks) could be influenced by groups of pollinators that are attracted to or repelled by certain floral bouquets. Species blooming in early spring emitted similar floral VOC blends containing generalist attractants, whereas floral VOC complexity was highest in mid to late summer. Forb species varied in the originality, uniqueness, and intraspecific variation (i.e. dispersion) of their floral VOCs, indicating the potential for different functional roles in plant-pollinator networks. Specifically, the originality, uniqueness and dispersion of forb species' floral VOCs increased across the growing season. Floral VOCs influenced forb interactions with pollinators. Floral VOCs contributed to the nested structure, but not modular structure, of community-level plant-pollinator network structure. Forb species with more original floral VOCs were less connected, while forb species emitting more compounds and with higher intraspecific variation in floral VOCs were more connected to pollinators. These findings show that floral scent plays important roles in structuring bee-forb interactions and guiding seasonal patterns in complex communities. Understanding seasonal patterns in floral VOCs may have important implications for plant-pollinator interactions among communities differing in species composition, or as shifts occur in suites of co-flowering species due to climate change. A free Plain Language Summary can be found within the Supporting Information of this article.