The effect of petal size manipulation on pollinator/seed-predator mediated female reproductive success of Hibiscus moscheutos |
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Authors: | Hiroshi Kudoh Dennis F Whigham |
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Institution: | (1) Smithsonian Environmental Research Center, P.O. Box 28, Edgewater, MD 21037, USA, US |
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Abstract: | The effects of petal-size manipulations on the behavior of pollinators and pollen/seed predators, and on pollen removal and
deposition, were studied in Hibiscus moscheutos (Malvaceae) populations. The ultimate effects on the female reproductive success of flowers, such as fruit set, seed predation
rate, and final seed set were also measured. We applied three levels of petal removal (100%, 50%, and 0% size reduction in
radius) to flowers in natural populations. Two pollinators (Bombus pennsylvanicus and Ptilothrix bombiformis) ignored flowers without petals, suggesting that pollinators use petals as a visual cue to locate flowers. Consequently,
100% petal removal reduced female reproductive success considerably, mainly through a higher rate of fruit abortion due to
failure of pollen deposition on stigmas. No significant differences between the 50% petal removal treatment and uncut control
were detected in any components of female success examined. The results, therefore, suggest that differences in petal size
have little influence on female reproductive success of Hibiscus flowers at our study site. Final seed set varied considerably depending on the larval densities of two coleopteran seed predators
(Althaeus hibisci and Conotrachelus fissunguis). A. hibisci responded to petal size, and a higher density of adults was found in flowers in which petal size had not been reduced. Because
Althaeus feed on pollen as adults and no effect of petal size on seed predation was detected, the preference of Althaeus for larger flowers may represent a foraging strategy for adult beetles and may exert counteracting selection pressure on petal
size through male reproductive success of flowers.
Received: 30 November 1997 / Accepted:12 June 1998 |
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Keywords: | Corolla size Fruit abortion Floral display Pollen predator Pre-dispersal seed predator |
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