Jason Vizelka, Jeffrey Karron, Randall Mitchell and Dorset Trapnell
Department of Biological Sciences, UW-Milwaukee, jvizelka@uwm.edu, karron@uwm.edu
Department of Biology, University of Akron, Akron, OH, rjm2@uakron.edu
Department of Plant Biology, University of Georgia, Athens, GA, dorset@uga.edu
Over the last decade there have been startling changes in the relative abundance and diversity of bumble bee populations, including significant decline of many species both in North America and Europe. Several species often coexist within a population and it is not known whether these species provide equivalent pollination services for native flowering plants. To address this question we quantified seed set of Mimulus ringens flowers following individual visits by Bombus fervidus, Bombus impatiens, and Bombus vagans. These three species coexist in native populations and vary considerably in both body size and foraging behavior. In 2012, mean seed number per fruit following single visits by Bombus vagans (X=3131) was significantly higher than mean seed number resulting from visits by B. impatiens (X=2423). In 2013, mean seed number per fruit was significantly different following visits by all three species. Species comparisons of self-pollination rate and mate diversity are currently being analyzed. These results suggest that different bumble bee species may have unequal contributions to native plant reproduction. Therefore local plant reproduction may be affected by changes in pollinator composition as well as by changes in pollinator abundance. In order to address how fluctuations in pollinator composition may affect local plant populations, current research is investigating how the exclusion of different bumble bee species influence local plant reproductive success. PhD dissertation research, Dr. Jeffrey Karron, Major Advisor.