Bee species exhibit different phenological trajectories in communities of annual flowering plants in the genus Clarkia

Abstract

Phenological matching between the timing of flowering and pollinator activity is critically important for the persistence of pollination systems globally. Phenological mismatch between plants and their insect pollinators can occur if flowering and adult insect activity do not occur simultaneously. There is evidence that the phenological trajectories vary among bee species, but little has been done to compare these trajectories with the phenology of the corresponding floral community. In this work, we use daily pan trapping across nine different annual Clarkia (Onagraceae) plant communities that vary in Clarkia species composition to estimate the phenological trajectory (within-season abundance curve) of the two most abundant bee pollinators - Lasioglossum incompletum, a generalist, and Hesperapis regularis, a Clarkia specialist - over the course of a Clarkia flowering season in California USA. Clarkia flower at the end of the winter annual growing season when all other winter annual plants have senesced, and therefore are phenologically separate from other flowering plants. We find that Hesperapis pollinator abundances follow the same phenological trajectory as Clarkia floral abundances in all community types. In contrast, Lasioglossum abundances do not track Clarkia floral abundance through time. Our results demonstrate that Clarkia exhibit closer phenological matching with Hesperapis than with Lasioglossum. These findings imply that pollinator communities may not respond monolithically to changes in the environment. Future research should study the phenological trajectories of plants and pollinators in different systems to determine if this pattern is common and repeatable.