Interspecific pollen loss by hummingbirds visiting flower mixtures: effects of floral architecture

Back in the field

In the field, (a) flowering Palicourea lasiorrachis often grow in mixtures with other flowers also visited by Lampornis (Feinsinger et al. 1991), (b) many Palicourea styles contain one or no pollen tubes whereas at least two are required for setting the full complement of two seeds, and (c) fruit set rarely approaches 100%, with a substantial proportion of fruits being single-seeded (Feinsinger et al. 1988, 1991). In previous field experiments, we concentrated on showing that neighboring flowers of Cephaelis, architecturally very similar to Palicourea [ILLUSTRATION FOR FIGURE 1 OMITTED], might sometimes be responsible for low pollination success in Palicourea (Feinsinger et al. 1991). It now appears that many or all of a Palicourea plant's neighboring guildmates, no matter how innocuous their distinctive reproductive architectures may appear, could affect that plant's pollen transfer just as strongly as would Cephaelis. For Palicourea and, we suspect, any other self-incompatible plant species with inconstant hummingbird pollinators, it's a jungle out there.

ACKNOWLEDGMENTS

B. Guindon helped greatly with all experiments, which would not have succeeded without his uncanny ability to coax hummingbirds into following the experimental protocols. W. Busby, H. Tiebout, and B. Young also provided help and advice. The Tropical Science Center permitted the work to occur in the Monteverde Cloud Forest Reserve, where W. Aspinall, G. Bell, W. Guindon, and A. Mendez provided facilities and logistical aid. W. S. Armbruster, T. Ayers, D. Campbell, L. McDade, M. Price, N. Waser, T. Whitham, and two anonymous reviewers gave valuable comments on drafts of the manuscript. D. Harrison drew Fig. 1. Financial support came from NSF grant BSR 8605043 and a University of Florida Graduate Research Assistantship.

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