FLORAL SYNDROME IN AMELANCHIER-NANTUCKETENSIS (ROSACEAE) - I - FLORALDENSITY, BEE ACTIVITY, AND CHARACTERIZATION OF ANDROPETALY

The clonal shrub Amelanchier nantucketensis is andropetalous; a variab le number of petals as well as normal anthers both bear germinable pol len. To determine whether floral density associated with andropetaly i s related to activity of native bees on flowers, we compared Amelanchi er nantucketensis to Amelanchier humilis and Amelanchier stolonifera, which have sterile petals. In samples from four Maine sites, floral de nsity in Amelanchier nantucketensis was 30.3% greater than that for Am elanchier humilis and 39.5% greater than that for Amelanchier stolonif era; in Amelanchier nantucketensis, flowers were more numerous per cub ic metre and distance between flowers was shorter. There was a signifi cant correlation across all sites and species between the number of fl owers per plant and number of inflorescences visited per bee in 10 min (r = 0.711, p = 0.0001). Statistical r tests separated Amelanchier na ntucketensis from both Amelanchier humilis and Amelanchier stolonifera by plant height, nearest stem, nearest flower, and number of inflores cences visited per bee during 10 min. Plant species classification in a canonical discriminant analysis was 83-93% correct with four plant v ariables, namely distance to nearest flower, distance to nearest inflo rescence, plant width, and plant height. Our findings support optimal foraging theory in that bee visits increase with floral density in the se Amelanchier species.