Floral syndrome in Amelanchier nantucketensis (Rosaceae). II. Bee preference and diversity associated with andropetaly

Abstract

Pollinator preference has been demonstrated to depend on floral morphology in some plant groups. We tested bee preference for Amelanchier nantucketensis, which has pollen-bearing petals or andropetals, over Amelanchier humilis with its normal petals when these flower together at two Maine sites. In an array experiment with equal floral display for Amelanchier nantucketensis and Amelanchier humilis, almost twice as many bees approached the latter first. Bees responded to some aspect of the larger flowers of Amelanchier humilis when number of inflorescences and height above the ground were similar. We captured 539 bees in 43 species individually on flowers, in malaise traps, and in sweeps; most were common, widely distributed solitary and eusocial bees. Bee species diversity differed slightly between plant species, and guilds differed; 11 bee species were unique to Amelanchier nantucketensis, including 39 individuals of Andrena milwaukiensis, and three species were unique to Amelanchier humilis. For 29 bee species shared by both plant species, abundance on Amelanchier nantucketensis was greater than on Amelanchier humilis for 62%, less for 14%, and the same for 24%. Bees might be attracted to Amelanchier nantucketensis less by andropetaly than by proximity of flowers to the ground, floral density, or unidentified features. Key words: Amelanchier, bees, foraging, morphology, Maine, species diversity.