Floral display in Narcissus: Variation in flower size and number at the species, population, and individual levels

Floral display (the size, number, and arrangement of open flowers) influenc es pollinator visitation to animal-pollinated plants and should be an impor tant determinant of reproductive success. We examined variation in the size and number of open flowers in wild daffodils (Narcissus). Our analysis of published data on 45 taxa showed that flower number varied negatively with flower diameter among Narcissus species, which supports the widespread assu mption that there is a trade-off between these traits. In contrast, field m easurements indicated a positive relation between flower number and diamete r within two populations of Narcissus dubius, and no relation was evident a fter we controlled for variation in bulb size. The discrepancy between inte r- and intraspecific patterns may have occurred because variable resource l evels obscure trade-offs when variation in flower size is low (e.g., within species). Size-related increases in floral tube length were half as great as corresponding increases in flower diameter, a result that is consistent with stronger stabilizing selection on tube length. Staggered flowering wit hin N. dubius inflorescences limited the mean number of open flowers to <66 % of total flower number, and slow expansion by later opening flowers resul ted in significant differences in flower size throughout flowering. Althoug h pollinators preferred large flowers, experimental reductions in flower di ameter did not affect seed production. Our results illustrate how the relat ive importance of the factors influencing floral display can vary among lev els of biological organization. Interspecific variation in flower size and number appeared to be constrained by allocation trade-offs, but intraspecif ic variation in both traits was more greatly influenced by plant resource s tatus. Within plants, the size and number of open flowers reflected the rel ative age of individual flowers and floral longevity.