Meeting Abstract

P3.39  Friday, Jan. 6  Competition Between Two Eurasian Plant Species for Pollinators: A Perturbation Experiment BARTHELL, J. F.*; HRANITZ, J. M.; ALBRITTON-FORD, A. C.; BARNETT, A.; BUTLER, M. E.; COWO, C. L.; KURTZ, R. M.; SANCHEZ, M. L.; WARREN, J. J.; PETANIDOU, T.; WELLS, H.; University of Central Oklahoma; Bloomsburg University of Pennsylvania ; Valdosta State University; State University of New York; Siena Heights University; University of Central Oklahoma; Commack High School; University of North Texas; Oklahoma State University; University of the Aegean; University of Tulsa

We studied competition for pollinators by two sympatric species of flowering plants on the island of Lesvos, Greece. One of these plant species, Centaurea solstitialis L., or yellow star-thistle, is a widespread, invasive species in the western USA. In the non-native environment, the species is highly attractive to pollinators, especially the non-native honey bee, Apis mellifera, L. However, at our (native) study site in Greece, far more large-bodied pollinators (including the honey bee) appeared to be attracted to nearby populations of chasteberry, Vitex agnus-castus L. We investigated whether pollinators would show an immediate preference for V. agnus-castus if it were suddenly made available to them foraging at C. solstitialis, as a perturbation effect. Accordingly, two transects of C. solstitialis were established with thirty inflorescences (kept alive in flower stem tubes) inserted into each transect at regular intervals. In one transect, hymenopteran pollinators (bees and wasps) were observed to visit the sprigs of V. agnus-castus in higher frequency than the C. solstitialis plants paired with them. However, in a higher density transect of C. solstitialis, we observed no such effect. These results suggest pollinators are guided by available nectar levels (standing crop) but that high densities of lower nectar standing crop species (e.g., C. sosltitialis) may draw them away from lower densities of a higher standing crop species (e.g., V. agnus-castus). A more nuanced perspective on foraging constancy by bees is therefore in order, with several factors (including genetic ones) determining how pollinators make foraging decisions.