Is Echeveria gibbiflora (Crassulaceae) fecundity limited by pollen availability? An experimental study

1. An experimental approach, manually pollinating all the flowers of individual plants, was used to measure the effect of pollen limitation on female fecundity of the hummingbird-pollinated perennial shrub Echeveria gibbiflora in the ecological preserve of Pedregal de San Angel around Mexico City, Mexico. Eleven randomly selected plants were manually over-pollinated in all their flowers and another 11 were left to be freely visited by natural pollinators, 2. Manually pollinated plants produced significantly more fruit and seeds than control plants (1-38 and 1.74 times, respectively). There was no change in average mass of fruits. 3. Considering individual fruit production per plant sampled three times in one season, decreases in fruit mass and average seeds per fruit Were observed within the same reproductive season for both treatments. For the manually pollinated plants, from the start to the end of the reproductive season, seed set decreased 55.9%; while in control plants seed set decreased 33.4% in the same period. For both treatments, average fruit mass decreased 26%. 4. Vegetative growth was not significantly different between control and experimental plants but hand-pollinated plants showed a smaller reproduction probability for the following year. 5. It is concluded that female fecundity in E. gibbiflora is limited by pollen early in the reproductive season and by resources in the middle and the end of the season.