Data from: Interaction intensity and pollinator-mediated selection

In animal-pollinated plants, the opportunity for selection and the strength of pollinator-mediated selection are expected to increase with the degree of pollen limitation. However, whether differences in pollen limitation can explain variation in pollinator-mediated and net selection among animal-pollinated species is poorly understood. In the present study, we quantified pollen limitation, variance in relative fitness and pollinator-mediated selection on five traits important for pollinator attraction (flowering start, plant height, flower number, flower size) and pollination efficiency (spur length) in natural populations of 12 orchid species. Pollinator-mediated selection was quantified by subtracting estimates of selection gradients for plants receiving supplemental hand-pollination from estimates obtained for open-pollinated control plants. Mean pollen limitation ranged from zero to 0.96. Opportunity for selection, pollinator-mediated selection and net selection were all positively related to pollen limitation, whereas nonpollinator-mediated selection was not. Opportunity for selection varied five-fold, strength of pollinator-mediated selection varied three-fold and net selection varied 1.5-fold among species. Supplemental hand-pollination reduced both opportunity for selection and selection on floral traits. The results show that the intensity of biotic interactions is an important determinant of the selection regime, and indicate that the potential for pollinator-mediated selection and divergence in floral traits is particularly high in species that are strongly pollen-limited.

在动物传粉植物中，选择机会与传粉者介导选择（pollinator-mediated selection）的强度，有望随花粉限制（pollen limitation）程度的升高而增强。然而，花粉限制的差异能否解释不同动物传粉物种间传粉者介导选择与净选择的变异，目前尚不明确。
本研究中，我们对12种兰科植物自然种群中的花粉限制、相对适合度变异，以及5个分别与传粉者吸引（开花始期、株高、花数、花大小）和传粉效率（距长）相关的性状的传粉者介导选择进行了量化。传粉者介导选择的量化方式为：从开放授粉对照植株的选择梯度（selection gradients）估计值中，减去接受补充人工授粉（supplemental hand-pollination）植株的选择梯度估计值。
平均花粉限制程度介于0至0.96之间。选择机会、传粉者介导选择与净选择均与花粉限制呈正相关，而非传粉者介导选择则无此关联。各物种间的选择机会差异达5倍，传粉者介导选择强度差异达3倍，净选择差异达1.5倍。补充人工授粉同时降低了选择机会与花部性状（floral traits）所受的选择压力。
研究结果表明，生物间相互作用（biotic interactions）的强度是选择体系（selection regime）的重要决定因素，并暗示在花粉限制程度较高的物种中，传粉者介导选择与花部性状分化的潜力尤为突出。