Hallett Allysa C, Mitchell Randall J, Chamberlain Evan R, Karron Jeffrey D
Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA.
Department of Biology, University of Akron, Akron, OH 44325, USA.
AoB Plants. 2017 May 27;9(3):plx020. doi: 10.1093/aobpla/plx020. eCollection 2017 May.
Pollinator abundance is declining worldwide and may lower the quantity and quality of pollination services to flowering plant populations. Loss of an important pollinator is often assumed to reduce the amount of pollen received by stigmas of a focal species (pollination success), yet this assumption has rarely been tested experimentally. The magnitude of the effect, if any, may depend on the relative efficiency of the remaining pollinators, and on whether the loss of one pollinator leads to changes in visitation patterns by other pollinators. To explore how a change in pollinator composition influences pollination of , we excluded bumble bees from plots in large and small populations of this milkweed species. We then quantified pollinator visitation rates, pollen export and pollen receipt for control plots and for plots where bumble bees were experimentally excluded. We found that exclusion of bumble bees did not reduce pollen receipt by flowers. Visitation by wasps increased markedly following bumble bee exclusion, both in small populations (186 % increase) and in large populations (400 % increase). Because wasps were as efficient as bumble bees at pollen transfer, increased wasp visitation offset lost bumble bee pollination services. Thus, loss of a frequent pollinator will not necessarily lead to a decline in pollination success. When pollinator loss is followed by a shift in the composition and abundance of remaining pollinators, pollination success will depend on the net change in the quantity and quality of pollination services.
传粉者数量在全球范围内正在减少，这可能会降低为开花植物种群提供的授粉服务的数量和质量。人们通常认为，重要传粉者的丧失会减少目标物种柱头所接受的花粉量（授粉成功率），然而这一假设很少经过实验验证。这种影响（如果存在的话）的程度可能取决于剩余传粉者的相对效率，以及一种传粉者的丧失是否会导致其他传粉者访问模式的改变。为了探究传粉者组成的变化如何影响这种马利筋物种的授粉情况，我们在该物种的大小种群的样地中排除了熊蜂。然后，我们对对照样地以及实验排除熊蜂的样地的传粉者访问率、花粉输出和花粉接收情况进行了量化。我们发现，排除熊蜂并没有减少花朵的花粉接收量。在排除熊蜂后，黄蜂的访问量显著增加，在小种群中增加了186%，在大种群中增加了400%。由于黄蜂在花粉传播方面与熊蜂一样高效，黄蜂访问量的增加抵消了熊蜂授粉服务的损失。因此，常见传粉者的丧失不一定会导致授粉成功率下降。当传粉者丧失后，剩余传粉者的组成和数量发生变化时，授粉成功率将取决于授粉服务数量和质量的净变化。
