Abstract

Little is known about the reproductive biology of the Crassulaceae. We studied a population of Echeveria gibbiflora in the Pedregal de San Angel ecological preserve in Mexico City, Mexico. Each flower is open and producing nectar 7 to 8 days. On the days of maximum nectar production (flowers 4-6 days old) an average of 14.5 mul accumulates in a flower per day. The maximum rate of nectar production is between 0700 and 0900 hours. The average sugar concentration in the nectar is 43.7%. In a given flower, pollen is exposed and the stigmas are receptive at the same time. The average natural fruit-set-and seed-set are 56.6% and 35.5%, respectively. The pollen-ovule ratio is 124, and the plants are fully self-compatible. The flowers are pollinated by only one species of hummingbird (Cynanthus latirostris) and are never visited by insects. Pollen movement is very limited (mean of pollinator flight distances = 0.72 m, mean distance fluorescent dyes = 0.92 m). Seed dispersion is by gravity and wind, and also is very limited (an average of 1.07 m). The total genetic neighborhood area is 15 m2 to 17 m2, producing a neighborhood effective population size (N(b)) of 5.01 to 39.7 individuals. This is a very small N(b), indicating that genetic drift may be a dominant force in the evolution of this species.