Kristin Powell

POLLINATION BIOLOGY AND BREEDING SYSTEMS OF CO-OCCURRING RARE AND INVASIVE CIRSIUM. Kristin Powell¹, Kyra Burraston¹, Tiffany Knight¹, Department of Biology, Washington University, St. Louis, MO¹

To determine the ecological causes and correlates of plant rarity and invasiveness, it is necessary to study plants that occur in similar habitats and are closely related. This study includes six species within the genus Cirsium that co-occur in northern California. These species range from endangered to noxious invaders. We found significant differences in the total reproductive success of these species, with the endangered species having the lowest seed output and the invasive species having the highest. We hypothesized that differences in reproductive success were due to differences in their pollination biology and breeding system. We quantified pollinator visitation rates and the composition of visiting species, and determined that the invasive plant species, Cirsium vulgare, attracted more pollinators than its non-invasive congeners. Further, Cirsium vulgare has an autogamous breeding system, whereas the other species required pollinator visitation in order to reproduce. We then conducted a pollen supplementation experiment to quantify the magnitude of pollen limitation across these species. However, despite variance in pollinator visitation rates and degrees of autogamy among species, none of the species showed significant levels of pollen limitation. This suggests that other factors besides pollination biology regulate the reproductive success and relative abundances of these species. Our future research will examine germination rates, resource availability and resource uptake abilities.