THE EFFECT OF THE DENSITY OF FLOWERING INDIVIDUALS ON THE MATING SYSTEMS OF 9 TROPICAL TREE SPECIES

Mating systems were examined through allozyme analysis for nine tropical tree species that occur on Barro Colorado Island, Republic of Panama. Estimates of outcrossing rates, using a mixed mating model, ranged from 0.35 to 1.08. Most species were highly outcrossed but two species that occurred at low densities had outcrossing rates below 0.7. Heterogeneity among trees in pollen allele frequencies contributing to progeny arrays was significant. The degree of heterogeneity in pollen allele frequencies was measured by Wright's F(ST), treating progeny arrays as populations. Mean F(ST) values were negatively correlated with flowering tree density, which indicates that trees at low density sample pollen from fewer individuals than trees in denser populations. Among-year heterogeneity in pollen allele frequencies for two species was also related to the density of flowering individuals; years with lower flowering tree density had greater heterogeneity and/or more selfing. These results indicate that several population parameters, such as inbreeding, genetic relatedness of progeny arrays, gene flow and effective population size are associated with the density of flowering individuals and thus vary from year to year and among locations.