AN EVALUATION OF THE PHYSIOLOGICAL AND EVOLUTIONARY INFLUENCES OF INFLORESCENCE SIZE AND FLOWER DEPTH ON NECTAR PRODUCTION

Contrasts proximate physiological explanations for the relation between nectar production per flower, number of flowers in an inflorescence and flower size with an evolutionary explanation based on competition for pollinators. Nine species in the Fabaceae with papilionaceous flowers and 8 species in the Ericaceae with urceolate flowers were analysed. Intraspecific patterns of nectar production indicate that source-sink dynamics and variation in plant size and/or vigour primarily affect nectar secretion rates within species. Interspecific patterns (production per flower declines patterns (production per flower declines with increasing inflorescence size) are also most consistent with a physiological explanation, namely the packaging of a limited allocation of photosynthate. Selection on the competing species to offer shared pollinators equivalent rewards seems to have had little effect on interspecific poatterns of nectar production. The frequency-dependent nature of pollinator attraction is probably the major constraint on evolutionary responses to competition for pollinators. -from Authors