PARENT SESSION
Oral Session #81: Pollination and Dispersal.
Presiding: T. Ricketts
Thursday, August 8. 9:00 AM to 11:30 AM. Grand Ballroom Central, Radisson.
Effects of an invasive plant on pollinator visitation to native plant species.
Larson, Diane*,1, Royer, Ronald2, Royer, Margaret3, 1 U.S. Geological Survey, St. Paul, MN2 Division of Science, Minot, ND3 U.S. Geological Survey, Jamestown, ND
ABSTRACT- Many alien plants form dense clones that flower profusely, introducing substantial amounts of alien pollen and nectar into the communities they invade. The increase in resources available to pollinators could enhance native plant pollination if many more pollinators are attracted, may depress native pollination if pollinators are preferentially attracted to the invasive species, or may depress effective pollination if inappropriate pollen transfer increases. In this study we recorded visitation by potential pollinators on 350 1-meter-square plots; plots had varying numbers of native and/or Euphorbia esula flowering stems. Insects were categorized to the lowest identifiable taxonomic level. Regression of number of visits on number of flowers for each of seven native plant species and E. esula revealed three primary patterns. Only visitors to Oxytropis lambertii were positively associated with flowering stems; bee and bumblebee visits were positively associated with native flower numbers (but not E. esula numbers) while fly and Lepidoptera visits were associated with E. esula flower numbers (but not O. lambertii). Lepidoptera visits were positively associated with flower numbers of three of the native species, but not with E. esula. Halictid bee visits to Linum perenne were unrelated to L. perenne flower numbers, but negatively associated with E. esula. The influence of an invader on pollination can thus be expected to vary, depending on the species of native plant and the identity of its primary pollinator.
KEY WORDS: pollination, invasive species, Euphorbia esula, Halictidae