Zorn-Arnold, Barbara , Howe, Henry F. .
Density and Seed Set in a Self-compatible Forb, Penstemon digitalis (Plantaginaceae), With Multiple Pollinators.
We used replicated plantings to identify factors that influence positive density-dependent effects of bumblebee behavior on seed production of Penstemon digitalis Nutt. (Plantaginaceae, hereafter Penstemon), a self-compatible, protandrous forb. Seed set per flower was 376% higher in the largest as compared with the smallest Penstemon patches. This Allee effect was associated with three factors: density and proportion of plants visited by long-tongued bumblebees were higher in larger than smaller patches of Penstemon, while the proportion of flowers visited per plant by long-tongued bees was lower in larger than smaller patches. Our results suggest that economics of flight and maneuverability of long-tongued bumblebees lead them to transfer more pollen between than within Penstemon plants in large patches. Density of short-tongued bumblebees was not positively associated with Penstemon seed set, but these smaller bees may be important for seed production at low plant densities. Pollen limitation, the difference in seed set between hand- and naturally pollinated flowers, was much lower in large than small Penstemon patches. Our Penstemon system extends well-recognized density effects of bee behavior on seed production of self-incompatible plants to a clear positive relationship between activity of effective pollinators and seed set in a self-compatible species.
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1 - University of Illinois-Chicago, Biological Sciences
Presentation Type: Oral Paper:Papers for Sections
Location: Williford B/Hilton
Date: Tuesday, July 10th, 2007
Time: 4:30 PM