H. Kudoh et Df. Whigham, The effect of petal size manipulation on pollinator/seed-predator mediatedfemale reproductive success of Hibiscus moscheutos, OECOLOGIA, 117(1-2), 1998, pp. 70-79
The effects of petal-size manipulations on the behavior of pollinators and
pollen/seed predators, and on pollen removal and deposition, were studied i
n Hibiscus moscheutos (Malvaceae) populations. The ultimate effects on the
female reproductive success of flowers, such as fruit set, seed predation r
ate, and final seed set were also measured. We applied three levels of peta
l removal (100%, 50%, and 0% size reduction in radius) to flowers in natura
l populations. Two pollinators (Bombus pennsylvanicus and Ptilothrix bombif
ormis) ignored flowers without petals, suggesting that pollinators use peta
ls as a visual cue to locate flowers. Consequently, 100% petal removal redu
ced female reproductive success considerably, mainly through a higher rate
of fruit abortion due to failure of pollen deposition on stigmas. No signif
icant differences between the 50% petal removal treatment and uncut control
were detected in any components of female success examined. The results, t
herefore, suggest that differences in petal size have little influence on f
emale reproductive success of Hibiscus flowers at our study site. Final see
d set varied considerably depending on the larval densities of two coleopte
ran seed predators (Althaeus hibisci and Conotrachelus fissunguis). A. hibi
sci responded to petal size, and a higher density of adults was found in fl
owers in which petal size had not been reduced. Because Althaeus feed on po
llen as adults and no effect of petal size on seed predation was detected,
the preference of Althaeus for larger flowers may represent a foraging stra
tegy for adult beetles and may exert counteracting selection pressure on pe
tal size through male reproductive success of flowers.