The worldwide decline in pollinators highlights the importance of understanding how factors associated with climate change may affect plant-pollinator interactions. Components of climate change have the potential to strongly influence plant traits important for attracting pollinators, including floral volatile organic compounds (VOCs). Because plant VOCs are information-rich signals that are highly responsive to the environment, studying floral VOCs and plant–pollinator interactions in the context of climate change could enhance our ability to form a more predictive understanding of how plant-pollinator interactions will change. We examined how drought and leaf herbivory—key components of climate change—affected floral display, floral volatiles, and the visitation rates and community composition of pollinators to four forb species in Montana (Campanula rotundifolia, Heterotheca villosa, Phacelia hastata, and Potentilla recta). Floral VOCs were collected and analyzed using headspace techniques and GC/MS. Pollinator visitation was assessed using timed field observations and flower visitors were captured and identified in the lab. VOC and pollinator community data were analyzed using multivariate techniques.
Leaf herbivory changed floral scent and reduced pollinator attraction in one forb species, Heterotheca villosa, but had no effect on the other three plant species. Experimental drought had larger impacts and significantly reduced flower size and floral display in all forb species. While drought had uniform impacts on visual floral traits, there were species-specific effects of drought on volatile emissions per flower, the composition of volatile compounds produced, and subsequent pollinator visitation rates. Drought also influenced the floral visitor community across forb species, indicating that some groups of pollinators were deterred while others were attracted. Together, these results indicate that VOCs may provide more nuanced information to potential floral visitors and may be relatively more important than visual traits for pollinator attraction, particularly under shifting environmental conditions.