Kudoh Hiroshi, Whigham Dennis F
Smithsonian Environmental Research Center, P.O. Box 28, Edgewater, MD 21037, USA, , , , , , US.
Oecologia. 1998 Nov;117(1-2):70-79. doi: 10.1007/s004420050633.
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.
在芙蓉葵（锦葵科）种群中，研究了花瓣大小操控对传粉者和花粉/种子捕食者行为、花粉去除和沉积的影响。还测量了对花朵雌性繁殖成功率的最终影响，如坐果率、种子捕食率和最终结实率。我们对自然种群中的花朵进行了三个水平的花瓣去除处理（半径减小100%、50%和0%）。两种传粉者（宾夕法尼亚熊蜂和蜂形毛带蜂）忽略了没有花瓣的花朵，这表明传粉者利用花瓣作为视觉线索来定位花朵。因此，100%的花瓣去除显著降低了雌性繁殖成功率，主要是由于花粉未能沉积在柱头上导致更高的落果率。在检查的雌性繁殖成功的任何组成部分中，50%花瓣去除处理和未切割对照之间未检测到显著差异。因此，结果表明花瓣大小的差异对我们研究地点芙蓉花的雌性繁殖成功率影响很小。最终结实率因两种鞘翅目种子捕食者（芙蓉锦斑象甲和裂缝锥象）的幼虫密度不同而有很大差异。芙蓉锦斑象甲对花瓣大小有反应，在花瓣大小未减小的花朵中发现了更高密度的成虫。由于芙蓉锦斑象甲成虫以花粉为食，且未检测到花瓣大小对种子捕食的影响，芙蓉锦斑象甲对较大花朵的偏好可能代表了成年甲虫的觅食策略，并可能通过花朵的雄性繁殖成功对花瓣大小施加抵消性选择压力。
