Breeding system, pollen limitation, and neighborhood effects on reproduction in two high-elevation Fuchsia species in Ecuador.

摘要

Despite the correlation between floral morphology and pollinator traits, pollen availability can limit seed production in outcrossing populations. If pollinator preferences and/or inter-specific pollen transfer decrease fitness, then closely related plant species with similar pollinators should experience selection on their floral traits via competition for pollen. I examined pollinator preferences by asking whether variation in neighborhood floral density or individual floral traits influenced hummingbird visitation and successful pollination for two species of Fuchsia, F. vulcanica and F. ampliata. I examined the effect of floral density at two different distances (5-10 m) by comparing hummingbird visitation to neighborhoods with different intra-specific, congeneric, and heterogeneric flowering densities. Results indicate that neither floral neighborhood or plant floral traits (number of flowers on a focal plant, corolla tube width and total amount of sugar present in the nectar) had an effect on pollinator preference. Thus, at the two dates tested (end of July, beginning of August) competition for pollen through pollinator preference between F. vulcanica and F. ampliata did not occur. To examine the effects of inter-specific pollen transfer, I carried out seven pollination treatments that tested for self-pollination, self-fertilization, pollen limitation, and pollen competition via inter-specific pollen transfer. Results indicate that both species are self-incompatible, do not produce seeds asexually or by self-fertilization, are pollen limited for seed set, and suffer reduced reproduction due to inter-specific pollen transfer. Therefore, any trait that reduces mixed pollen loads may be selected for within these populations. Finally, results suggest that localized breeding within the 5 m neighborhood could lead to inbreeding depression for both species.