Richardson Sarah C
Indiana University, Department of Biology, Jordan Hall 015, Bloomington, IN 47405, USA.
Oecologia. 2004 Apr;139(2):246-54. doi: 10.1007/s00442-004-1504-8. Epub 2004 Feb 7.
As "exploiters" of plant-pollinator mutualisms, nectar-robbers remove rewards (nectar) without providing pollination services. Though one might expect nectar-robbing to be costly to plants, it may instead benefit plants by indirectly increasing pollen dispersal. I investigated the direct effects of nectar-robbing bees ( Xylocopa californica) on floral rewards and behaviors of pollinators visiting desert willow ( Chilopsis linearis) and indirect effects of robbing on the reproductive success of the plant. Nectar-robbers reduced nectar; while unrobbed and robbed flowers were equally likely to contain nectar, nectar volumes were smaller in robbed flowers with nectar. Apis mellifera (honeybees), ineffective pollinators in terms of pollen deposition, avoided robbed flowers. In contrast, Bombus sonorus (bumblebees), effective pollinators, did not avoid robbed flowers. While bumblebees tended to spend less time in robbed flowers, the time that they spent in flowers was not correlated with pollen deposition. Using powder mimicking pollen, I found that on some days, powder was dispersed farther or to more flowers from robbed flowers, indicating that robbing may sometimes benefit plants by increasing male reproductive success. Powder movement suggested that the effect of robbing on male reproductive success ranged from costly to beneficial. The outcome for flowers that were marked early each morning was a function of prevalence of robbing and abundances of effective pollinators, but not a function of spatial variability among trees in prevalence of robbing or the abundance of ineffective honeybees. Unlike powder dispersal, female reproductive success, measured by fruit set and the number of pollen tubes growing in styles, was not affected by robbing. Thus, robbers did not reduce plants' female reproductive success either directly by damaging flowers or indirectly by reducing pollen deposition by pollinators. Overall, this study indicates that nectar-robbers were not often costly to plants, and sometimes even benefited plants.
作为植物 - 传粉者互利共生关系的“剥削者”，盗蜜者获取了报酬（花蜜）却不提供传粉服务。尽管人们可能认为盗蜜对植物代价高昂，但它反而可能通过间接增加花粉传播而使植物受益。我研究了盗蜜蜜蜂（加州木蜂）对访问沙漠柳（线叶奇子树）的传粉者的花部报酬和行为的直接影响，以及盗蜜对该植物繁殖成功的间接影响。盗蜜者减少了花蜜量；虽然未被盗和被盗的花朵含有花蜜的可能性相同，但有花蜜的被盗花朵的花蜜量较小。西方蜜蜂（蜜蜂）在花粉沉积方面是无效传粉者，会避开被盗花朵。相比之下，有效传粉者熊蜂不会避开被盗花朵。虽然熊蜂在被盗花朵上停留的时间往往较短，但它们在花朵上停留的时间与花粉沉积无关。使用模拟花粉的粉末，我发现有些日子里，粉末从被盗花朵传播得更远或传播到更多花朵上，这表明盗蜜有时可能通过提高雄性繁殖成功率而使植物受益。粉末移动表明盗蜜对雄性繁殖成功的影响从代价高昂到有益不等。每天清晨标记的花朵的结果是盗蜜发生率和有效传粉者数量的函数，而不是树木间盗蜜发生率的空间变异性或无效蜜蜂数量的函数。与粉末传播不同，通过坐果率和花柱中生长的花粉管数量衡量的雌性繁殖成功不受盗蜜影响。因此，盗蜜者既没有直接通过损坏花朵，也没有间接通过减少传粉者的花粉沉积来降低植物的雌性繁殖成功。总体而言，这项研究表明盗蜜对植物并不常有高昂代价，有时甚至使植物受益。
