Floral Resource Variation, Pollinator Response, and Potential Pollen Flow in Psiguria Warscewiczii

Abstract

Fluorescent dyes were used to examine several hypothesized ecological correlates of pollen flow in a natural population of a tropical, butterfly—pollinated vine, Psiguria warscewiczii. The study population consisted of monoecious, perennial vines that flower year round, have a flowering peak during the rainy season, and possess an extreme bias in proportion of flowering plants in male phase. Number of flowers on individual plants, flower density, and pollen surplus in staminate flowers at the end of the day (an indicator of visitation activity, or average resource availability) were monitored periodically over 4 yr from 1980 to 1984. Also monitored were the accumulated number of conspecific pollen grains on stigmas, and presence or absence of tephritid fly larvae (Blepharoneura sp.), which infested between 0 and 15% of the staminate flowers sampled. Local flower density (measured within 50 m of the dye—source plant) explained °50% of the variation in mean dye—dispersal distance. Visitation rate, number of individual visitors, and floral occupation rates of individually marked Heliconius butterflies were negatively correlated with average pollen surplus in staminate flowers. At very low levels of resource availability, many butterflies defended individual flowers for entire mornings against repeated attempts by other butterflies to visit the same flowers; at higher resource levels, butterfly visits were of shorter duration, and more movement among plants was observed.