EFFECTS OF DISPLAY SIZE,FLOWERING PHENOLOGY,AND NECTAR AVAILABILITY ON EFFECTIVE VISITATION FREQUENCY IN COMPARETTIA FALCATA (ORCHIDACEAE)

Comparettia falcata is an epiphytic, neotropical orchid that produces nectar as a pollinator reward. In Puerto Rico, C. falcata is allogamous and pollinated by the endemic hummingbird Chlorostilbon maugaeus. Autogamous pollinations are possible, but may result in reduced fruit set. For the 1989 and 1990 flowering seasons, the probability of pollinarium removals and natural pollinations increased with individual inflorescence display size. However, the frequency of effective pollinator visits was independent of flowering phenology in both years. A positive correlation between inflorescence size and reproductive success occurred in 1990 but not in 1989. In 1990 plants produced longer spurs, a higher standing crop of nectar, and a more concentrated nectar than in 1989. There was no relation between nectar availability (= standing crop of nectar) and sugar concentration in either year. Nectar availability and sugar concentration did not vary among the first four flowers of an inflorescence in either season. Nectar availability was not a good predictor of effective visitation. Comparettia falcata has a higher natural fruit set than tropical deceptive orchids, suggesting that pollinator visitation may be enhanced by nectar reward. The small, dilute nectar volumes secreted by C. falcata may benefit the plant by increasing interplant pollinator movement and pollen dispersal.