Conservation impact of climatic variability on pollination of the federally endangered plant, Clematis socialis (Ranunculaceae)

Biotic pollination should be an important consideration when devising management plans for endangered plant species. In this study we documented inter-annual shifts in the suite of floral visitors to Clematis socialis, a federally endangered species. These pollinator shifts were correlated with shifts in climatic variables that we used as a proxy for the potential effects of climatic change. In addition, we characterized floral visitor behavior and conducted single-visit seed set experiments to assess the pollination effectiveness of floral visitors. Five insect species visited flowers of C. socialis: two lepidopteran species (Erynnis juvenalis and Hemaris diffinis) and three bee species (Anthophora ursina, Bombus pennsylvanicus and Xylocopa virginica). Due to their relatively greater frequency of flower visitation and high single-visit seed set (ca. 2.6-3 seeds/visit), two bee species (Anthophora ursina and Bombus pennsylvanicus) are considered to be the major pollinators of C. socialis. However, the relative importance of each pollinator species varied between years. Anthophora ursina was the most important pollinator in 1997, a year when C. socialis bloomed later in the spring. Queens of Boinbus pennsylvanicus were the primary pollinator during 1996, a year when C. socialis bloomed relatively early in the spring. We conclude that management plans that focus on the "best pollinator" of a suite of pollinators may not preserve the long-term reproductive integrity of endangered plants with generalized pollination systems. We further conclude that asynchrony between flowering season and pollinator activity patterns may be a risk factor associated with human-caused global climate change.