Pollen supply limits fruit initiation by a rain forest understorey palm

1 I studied the effect of independent variation in pollen supply and resources (plant size and light availability) on fruit production by Calyptrogyne ghiesbreghtiana, assessing fruit initiation on a per flowering episode basis. Since this species shows no abortion of fruit between initiation and ripening (although many fruit are eaten by insects), any effect of pollen supply or resource availability limiting fruit production will be most apparent at fruit initiation. 2 Variation in visitation by bats, the pollinators of this species, was correlated with fruit initiation. A survey of pollen loads on 642 bat-visited female flowers revealed, however, that pollen transfer by bats was frequently ineffective. Even after bat visitation, 46% of flowers remain unpollinated. 3 Controlling the supply of pollen to inflorescences at two levels (155 flowers vs. 50 flowers per inflorescence) revealed that the number of fruit initiated per inflorescence is significantly affected by pollen supply. At the high level of controlled hand-pollination the median number of fruit initiated per infructescence was almost five times greater than in the naturally pollinated population. 4 Variation in plant size, light availability, and the number of flowering episodes in the previous year, failed to explain any of the variation in fruit initiation by the unmanipulated field population, or the hand-pollinated population. The resource environment is, however, important to lifetime reproductive success because of its influence on flowering frequency. 5 To my knowledge, there are no other field studies of reproduction by non-herbaceous perennial plants that examine the effect of independent variation in both pollen supply and the resource environment.