Phenology is a critical life history trait of organisms with consequences for their survival, reproductive success, and interactions with other species. Climate change has been shown to alter the phenologies of plants and animals, in some cases causing phenological mismatches. Although phenological mismatches within predator-prey and plant-herbivore interactions have been documented, their occurrences and consequences within mutualistic interactions, such as plant-pollinator interactions, have received less attention. Investigating how climate change will affect plant-pollinator interactions is crucial because nearly 90% of flowering plants rely on insects or other animals for pollination. The goal of this study was to determine how altered flowering phenology affected plant-pollinator interactions, plant reproductive success, and the mechanisms involved. We manipulated flowering phenology by altering snowpack (snow removal vs. control treatments) in the Rocky Mountains of Colorado. We measured flowering phenology, floral morphology, pollinator visitation, and reproduction (fruit and seed set) of four native flowering species. In addition, we performed hand-pollination experiments within snow manipulation plots to determine how pollen limitation varied with flowering phenology.
Results/Conclusions
Date of peak flowering occurred significantly earlier for all focal species (mean of 8.25 days) in snow removal plots than control plots, and the effect was equally strong for early-, mid- and late-season species. Flowering duration was not affected by snow removal. Floral characters important for pollinator visitation varied significantly with snow removal treatments, although the direction was species specific. For example, in snow removal plots, mean petal length increased by 15% in Delphinium nuttallianum (Ranunculaceae) but decreased by 13% in Potentilla pulcherrima (Rosaceae). The strength of pollen limitation varied with snow removal treatments. For example, in Claytonia lanceolata (Portulacaceae), seed-set was significantly higher in hand pollination treatments in snow removal plots but not controls, suggesting that reproduction in snow removal plots – but not control plots – would have been higher given increased pollinator visitation. Our results suggest that altered phenology can affect floral attractive traits and pollen limitation, thus changes in pollinator visitation could have dramatic consequences for plant fitness. Our results highlight that plant-pollinator interactions and plant reproduction could be affected by altered phenology although the effect could be due to phenological mismatches and/or changes in floral characters that could affect pollinator visitation.