An experimental study of floral display and fruit set in Chilopsis linearis (Bignoniaceae)

To examine the effects of pollen and resource availability on floral display and fruit set in Chilopsis linearis three different types of experimental manipulations were performed. Pollen availability to individual inflorescences was altered by combinations of hand-pollinations and/or pollinator exclusions. Number of flowers produced per inflorescence was determinate; it was not affected by pollination, although flowers of the unpollinated treatment lasted longer. Fruit set was increased over natural levels by an average of 540% by hand-pollinating individual inflorescences. There was also a negative correlation between inflorescence size and percent fruit set in all treatments tested. Attempts to vary resources available to individual inflorescences and entire trees showed no significant effect on fruit set. These results show that, at the level of individual inflorescences, fruit and seed production in Chilopsis linearis are pollen limited and not resource limited. The problem of testing for resource limitation of female reproductive success in iteroparous plants and the effect of inflorescence size on female components of fitness are also discussed.