Climate change is shifting the flowering phenologies of plant species across the planet, resulting in alterations in co-flowering patterns. However, the consequences of climate-driven changes in co-flowering have not been studied. Using a short-term field experiment based on results from a long-term flowering phenology dataset in the Colorado Rocky Mountains, USA, we examined how shifts in co-flowering, or temporal synchrony, between Linum lewisii and Potentilla pulcherrima are affecting the reproductive success of Linum. Long-term data show reduced flowering synchrony between Linum and Potentilla as the climate changes. I therefore created reduced synchrony treatments in which Potentilla flowers were removed (50% and 100% removal), in addition to an unmanipulated control. Pollinator visitation, pollen deposition, fruit and seed set, and total seeds were measured on Linum plants to determine how changes in synchrony with Potentilla affected its pollination and reproductive success. Each synchrony plot was subdivided into control and pollen addition treatments to determine whether Linum reproduction was pollen limited. Additionally, a watering treatment was applied to half the plots because 2018 was an extremely dry year. Based on previous work on competition for pollination, we hypothesized reduced synchrony would lead to less competition for pollinator services and higher Linum reproductive success.
Results/Conclusions
Flowering synchrony had no effect on pollinator visitation rate, the number of pollinator visitors, or the number of Linum pollen grains on stigmas. However, reduced synchrony was associated with a higher percentage of conspecific pollen grains. For all of our reproductive responses, reduced synchrony was associated with significantly higher reproductive success, but only in the watering treatment. These results suggest that the watering treatment enhanced reproductive output compared to controls during a very dry year, and allowed us to detect an effect of synchrony on fruit and seed set and total seeds produced. Additionally, consistent with our pollinator visitation and pollen quantity results, there was no difference in the magnitude of pollen limitation among plants supplemented with pollen and control plants, indicating that Linum is not pollen limited. Our results suggest that plants experiencing less synchrony had enhanced reproductive output because they received a higher percentage of conspecific pollen deposition. Therefore, climate change may have positive effects on the pollination and reproduction of some plant species via reductions in temporal synchrony of species that compete for pollination. Our study also suggests that the biotic effects of climate change can be overridden by extreme abiotic environments, in this case drought.