15 - The effects of floral design and display on pollinator economics and pollen dispersal

Summary

Animal pollination is a mixed blessing for angiosperms. Animals carry pollen readily because they are mobile and large relative to pollen grains. Furthermore, animals learn to associate floral signals with the presence of food and so move between conspecific plants relatively consistently (Chittka et al., this volume; Gegear & Laverty, this volume; Giurfa, this volume; Menzel, this volume). However, animals act in their own interests, which often conflict with successful pollen transport (e.g., only about 1% of a plant's pollen production reaches stigmas; Harder 2000). Consequently, manipulation of pollinator behavior to promote cross-pollination is a prevailing theme in the evolution of floral design (form, color, nectar, and fragrance production) and display (inflorescence size and architecture).

This chapter reviews three aspects of pollinator manipulation by plants and their effects on pollen dispersal. First, because pollen dispersal for most animal-pollinated plants depends on the general responses of feeding pollinators to their foraging environment, we consider the underlying economic principles that establish the opportunities for floral manipulation. Second, we outline influences on the typical pattern of pollen dispersal among flowers for plants with granular pollen, and summarize how flower design affects this pattern (for a review of dispersal of orchid pollen, see Harder 2000). Finally, because pollination and mating success are characteristics of entire plants, rather than individual flowers, we consider how floral display affects pollinator attraction and within-plant behavior to determine pollen dispersal.