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

Abstract

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.

Phenotypic Trait Variation in Populations of a Global Invader Mayweed Chamomile (Anthemis cotula): Implications for Weed Management

“…Alternatively, as it occurs with some other invasive plant species (e.g., Miller et al, 2018), the long flowering period in some A. cotula populations might help compete for pollinators that they share with native species. Variation in floral scent VOCs among A. cotula populations also could reflect adaptation to local environmental conditions such as soil moisture (Burkle and Runyon, 2016;Campbell et al, 2019) and the diversity and abundance of local pools of flower visitors (Burkle and Runyon, 2019;Kantsa et al, 2019). Although these patterns in our data could result from local adaptation, climatic and edaphic variables explained only a small proportion (0.013, i.e., 1.3%) of the total variation in phenotypic traits.…”

Using Matching Traits to Study the Impacts of Land-Use Intensification on Plant–Pollinator Interactions in European Grasslands: A Review

“…By modifying plant communities, intensification affects grassland odourscapes, which are assemblages of volatile organic compounds (VOCs) emitted by plants, and in turn alters plant-pollinator interactions [53] and the structure of pollination networks [54]. The only experiment (to the best of our knowledge) that tests this hypothesis [36] found no relationship between botanical composition at the community level after intensification and VOCs.…”

“…For example, [36] found a positive correlation between the relative abundance of benzaldehyde and bumblebee species richness and between the relative abundance of butyrolactone and bee species richness. Furthermore, [54], in the Northern Rocky Mountains of the U.S., showed that the richness of bees (standardized by subnetwork size) increased with floral VOC richness and declined with VOC originality.…”

Plant-insect chemical communication in ecological communities: an information theory perspective

“…Studies on plant VOCs have revealed that some VOCs are more frequent than others (Farré-Armengol et al, 2020;Knudsen et al, 2006), but the detailed information structures have not been explicitly studied. To explore the redundancy of plant chemical language and whether the frequency of its vocabulary (VOCs) follows Zipf's law, we gathered the data from the only four community-level plant VOC studies so far, three of which focused on floral VOCs in plant-pollinator networks (Burkle and Runyon, 2019;Filella et al, 2013;Kantsa et al, 2017) and one on leaf VOCs in a plant-herbivore (caterpillar) network (Zu et al, 2020). Additionally, we also use a review study by Farré-Armengol et al 2020(Farré-Armengol et al, 2020, who compiled a floral VOC dataset from 305 species.…”

“…From the four community-level plant VOC studies which documented the PV-matrix, three of them (Burkle and Runyon, 2019;Kantsa et al, 2019;Zu et al, 2020) also document insect-plant interaction networks (AP-matrix) in the same community. We found that plant coding patterns vary from community to community (Fig.…”