Adaptations for the 'Fail-safe' Pollination of Specialized Ornithophilous Flowers

Abstract

-The efficiency of a plant-pollinator mutualism may be enhanced, but the predictability of pollination may be reduced, by increased specialization of the interaction. We propose that these potentially strong, opposing selection pressures may have important consequences for the morphology of hummingbird-pollinated flowers, specifically influencing morphology of the nectar chamber and the adjacent corolla tube in relation to nectar production rates. The size of the nectar chamber may limit access at low reward levels to primary pollinators, but if these pollinators are uncommon or absent, nectar rewards predictably may be made available to secondary pollinators. We illustrate this suggested morphological adaptation with data from 14 Costa Rican species of Heliconia (Musaceae).