Does beak size predict the pollination performance of hummingbirds at long and tubular flowers? A case study of a Neotropical spiral ginger

Long-billed hummingbirds are assumed to be better adapted than short-billed ones for the pollination of long tubular flowers. However, the majority of the empirical evidence is derived from surveys of pollinator feeding performance, which tend to ignore the implications for plant fitness. Here, we tested the long-billed performance hypothesis from the perspective of the pollinated plant. We conducted a comparative survey to evaluate fecundity in relation to the length of the beak of the pollinating hummingbirds visiting the long and tubular flowers of Costus spiralis (Costaceae), in the Brazilian Atlantic forest. The flowers of C.spiralis were pollinated by three hummingbird species and their nectar was thieved by the bee Eulaema sp. There was no significant difference in the frequency of floral visits nor in the production of seeds among the three hummingbirds in fruits formed from flowers exposed to a single visit by each pollinator. Unexpectedly, our results indicate that the floral morphology of C.spiralis is equally compatible with long- and short-billed pollinators, and is apparently incompatible with pollination by large insects. These findings emphasize the need to test the performance of each floral visitor with the simultaneous estimation of the intensity of the interactions, to increase the accuracy of the measurement of the pollinator's relative importance in studies of plant-pollinator interactions in ornithophilous systems.