OOS 15-9
Phenological mismatch with bees and unfavorable abiotic conditions reduce Claytonia lanceolata reproduction in phenology field experiments
Phenology is a critical life history trait with consequences for organisms’ survival, reproduction, and interactions with other species. Climate change has been shown to alter the phenologies of plants and animals, in some cases causing phenological mismatches between interacting species. Although phenological mismatches have been documented in predator-prey and plant-herbivore interactions, their occurrence and consequences in 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 investigate how altered flowering phenology affected plant-pollinator interactions, plant reproductive success, and the mechanisms involved. We experimentally altered flowering phenology of Claytonia lanceolata (Portulacaceae) using two methods: in 2011-2013 by altering snowpack (snow-removal vs. control treatments), and in 2013 by inducing flowering in a greenhouse before placing plants in experimental outdoor arrays (early, control, and late phenology treatments). We measured flowering phenology, pollinator visitation, and reproduction (fruit and seed set). In addition, we performed hand-pollination experiments within phenology treatments to determine how pollen limitation varied with flowering phenology.
Results/Conclusions
Flowering occurred approximately ten days earlier in snow-removal than control plots during all years of snow manipulation. Snow removal affected soil moisture, causing changes in water potential and floral characters important for pollinator visitation. The strength of pollen limitation varied with snow-removal treatments and among years. In 2011 and 2013, seed-set was higher in hand pollination treatments in snow-removal but not control plots, suggesting that reproduction in snow-removal plots was limited by pollen receipt. C. lanceolata was not pollen limited in 2012 due to severe frost events and almost complete failure to reproduce. In the array experiment, we manipulated our early treatment to bloom ten days ahead of controls, but did so without affecting soil conditions. Early phenology plants were not pollen limited but almost completely failed to reproduce due to severe frost, despite high pollinator visitation. Moreover, late phenology plants were severely pollen limited due to low pollinator visitation. Control plants, on the other hand, were not pollen limited and achieved the highest plant fitness. Taken together, our results suggest that advancing flowering times puts plants more at risk of frost damage and, in some years without concomitant changes in pollinator phenology, may exacerbate pollen limitation of plant reproduction.