Linking pollination and plant community ecology: Decoupled vegetative and reproductive responses

Background/Question/Methods

Individual species vary in their responses to environmental conditions, often, but not always leading to changes in the community. Pollination ecology largely focusses on the ecology of a small number of species but does not usually translate these results to changes in the community. For example, changes in the abiotic or biotic environment can alter flowering in a given species, but we do not know how this changes flowering for the whole plant community. Similarly, changes in flowering can affect floral visitation for particular species, but it remains unclear what determines the distribution of floral visits across the community. To address these issues, we monitored the vegetative and reproductive responses of plant communities in a factorial experiment with 160 plots manipulating fungi, nutrients, and plant litter. For 18 common insect-pollinated plants, we estimated vegetative cover monthly and flowering and visitation bi-weekly, where we counted over 23500 flowering stems and observed 7400 insect visits to individual flowering stems. Specifically, we compared individual species responses to that of the community for both vegetative and reproductive responses to the treatments. We also assessed whether experimental effects showed consistent effects on vegetative growth, flower production, and floral visitation across the plant community.

Results/Conclusions

Individual insect pollinated species varied hugely in both their vegetative and reproductive responses by treatment with every treatment combination affecting at least one species; however, as a community, we only saw changes in reproductive responses. Summed across the community, litter removal increased flowering, while fungal suppression and fertilization decreased floral richness and evenness, but changes were small (5-10%). These changes in the flower community were the dominant factor behind changes in total visits to the community, which also affected the distribution of floral visits across the flowering community. We also found large changes (10-30%) due to treatment effects on the distribution of floral visits among flowering species, independent of changes to the flowering community, perhaps due to unmeasured floral characters. Our results suggest that although individual species may be sensitive to experimental treatments, this does not necessarily change the plant community. They also show a decoupling of vegetative and reproductive responses for plant communities, with reproductive responses being more sensitive to the treatments. These reproductive responses manifested as both changes in flowering and the distribution of visits among flowers. Such changes have potential implications for plant community dynamics that may be missed if we only measure vegetative responses.