Evol Ecol Res 7: 901-913 (2005)     Full PDF if your library subscribes.

Conditional strategies in an animal-pollinated plant: size-dependent adjustment of gender and rewards

Jay M. Biernaskie* and Elizabeth Elle

Behavioural Ecology Research Group, Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia V5A 1A6, Canada

Address all correspondence to Jay M. Biernaskie, Department of Zoology, University of Toronto, 25 Harbord Street, Toronto, Ontario M5S 3G5, Canada.
e-mail: jmbierna@zoo.utoronto.ca


Question: How do hermaphroditic flowering plants that must attract animal pollinators allocate to flower production, seed production and nectar production among flowers, as functions of their individual size and the size of their floral display?

Organism: Chamerion (= Epilobium) angustifolium; vertical inflorescences display male-phase flowers above female-phase flowers.

Site: Silver Star Mountain, Vernon, British Columbia, Canada.

Methods: We measured nectar production from male- and female-phase flowers across a range of display sizes. By experiment, we determined the effect of alternative nectar distributions on bumblebee foraging. We measured total flower production (male investment), seed production (female investment) and plant size.

Results: Large floral displays allocated extra nectar production to female-phase flowers. Bumblebees probed fewer male-phase flowers per visit when extra nectar was added to female-phase flowers than when nectar was added more evenly among gender phases. Large plants produced about a third fewer flowers per gram of plant biomass than did the smallest plants. But large plants matured a nearly proportional number of seeds.

Keywords: bumblebees, Chamerion, Epilobium, inflorescence design, nectar gradient, nectar production rate, patch departure, pollen dispensing, sex allocation.

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