PARENT SESSION
Oral Session #28: Plant-Animal Interactions. Presiding: S. Louda.
Tuesday, August 7, 2001. 8:00 AM to 12:00 PM. Hall of Ideas J.
Effect of Lupinus perennis population size and local density on pollinator behavior.
BERNHARDT, CHRISTOPHER1, MITCHELL, RANDALL1, MICHAELS, HELEN2, 1 2
ABSTRACT- To determine the cause of lowered reproductive success in small Lupinus perennis populations of northern Ohio and Southwestern Michigan, we examined the response of pollinators to population size and local density. We addressed the following questions 1) Does population size and density affect pollinator behavior (e.g. pollinator visitation rates)? and 2) Does population size and density affect the number of pollen tubes found in an ovary? We hypothesized population size and plot density will affect pollinator behavior, manifested in higher visitation rates in large populations and dense plots causing an increase in the number of pollen tubes in ovaries. To address our questions, for two field seasons we studied five small (<1,000 plants) and five large (>1,000) lupine populations paired together according to physical features, proximity, phenology, and agency ownership. Within each pair, we conducted simultaneous 15-minute pollinator observations. We found that pollinator visitation rates were significantly higher in dense plots but did not vary with population size. Also, pollinators visited more flowers on an inflorescence in dense areas of large populations. We also found the number of pollen tubes in an ovary significantly increased with local plant density, confirming that the observed changes in pollinator behavior with density affect pollination. Overall, we found that pollinator behavior responded strongly to local density, but little or no indication that pollinator service varied with population size.
KEY WORDS: Pollination, Lupinus perennis, Bombus, Density Effects