Spatial and temporal variation in pollinator behavior in two subspecies of Oenothera cespitosa (Onagraceae)

Pollination success of insect-pollinated plants is influenced by various factors such as the abundance, diversity, visitation frequency and diel activity patterns of pollinators. A growing body of empirical evidence suggests that spatiotemporal variation in foraging behavior and pollinator effectiveness can strongly influence plant reproductive success. We examined the spatiotemporal variation in foraging behavior of the pollinators of two subspecies of Oenothera cespitosa (Onagraceae), a night-blooming plant in western North America. Night blooming flowers of O. cespitosa remain open the following morning, providing nectar and pollen as potential rewards to moths and crepuscular bees. We compared the composition of the pollinator communities associated with each subspecies during morning and evening field observations. In Jackson Hole, WY, we found that both the pollinator community composition and visitation patterns among pollinators varied significantly for O. c. cespitosa. Most visits occurred at dawn and the two main visitors were solitary bees in the genera Lasioglossum and Andrena. In Moab, UT, floral visits to O. c. navajoensis occurred mainly at dusk and the principal visitors were carpenter bees (Xylocopa spp.) and the white-lined Sphinx moth (Hyles lineata). Field experiments will characterize and compare the variation in pollinator effectiveness of each visitor to both subspecies of Oenothera cespitosa.