Habitats, Trade Winds, and Pollination of the EndangeredCycas micronesica: Is There a Role for Wind as Pollen Vector on the Island of Guam?

Premise of research. The role of specialist insects in the pollination of cycads is well established, with wind playing little to no role. Questions remain for species within theCycas rumphiicomplex that have dispersed via floating seeds to islands far from mainland ancestors. One such species,Cycas micronesica, resides in habitats on the island of Guam that are exposed to trade winds that enhance the potential for wind pollination. Methodology. We examined the distance and direction of horizontal pollen movement either from microstrobili or from experimentally released pollen relative to wind direction and velocity in several different Guam cycad habitats. Wind-dispersed pollen was also captured around megasporophylls and then examined relative to wind and distance from dehiscing microstrobili. Pivotal results. Wind velocity, trap direction, and trap distance from the pollen source were the most important factors affecting pollen capture. In habitats whereC. micronesicagrows in the deep understory with 2 m/s, some downwind traps captured significant pollen even at 32 m but with a dramatic decrease after 8 or 16 m, and upwind traps captured little pollen. Pollen capture around megasporophylls was substantial for those up to the experimental limits of ∼6 m downwind from a dehiscing microstrobilus. Conclusions. These results, along with previous studies that verified specific insect associations with reproductive organs ofC. micronesica, indicate ambophily but with a stronger role for wind as a pollen vector than in previousCycasstudies. However, wind as a vector is limited to open areas or forested habitats with some exposure to winds and is not found in deep understory habitats.