Anthecology and pollinator efficacy of Styrax officinale subsp. redivivum (Styracaceae)

Styrax officinale subsp. redivivum is a homogamous, xenogamous shrub of the California foothill chaparral. Its floral biology, breeding system, and pollination ecology are presented. A summarizing model of pollinator efficacy, EP, describes the relative potential of pollinator species based on behavioral, morphological, and ecological variables. The EPcan be expressed as the product of pollinator density (number per flower per minute) and individual pollinator efficacy. By this analysis, the most individually efficacious pollinator of S. o. redivivum is the papilionid butterfly Battus philenor. Pollen forager honey bees, Apis mellifera, are important on a population level but, on an individual basis, are less efficacious than queens of the bumble bee Bombus vosnesenskii. Nectar foraging honey bees, Bombus edwardsii workers, and females of the carpenter bee Xylocopa tabaniformis have intermediate values. The halictid bee Halictus ligatus has little importance as a pollinator and syrphid flies have almost no potential.