Supplementary material for: No decoy effect in bees: rewardless flowers do not increase bumblebees' preference for neighbouring flowers

ABSTRACT

Nectarless flowers are common among flowering plants, which often retain colour-changed, rewardless flowers instead of shedding them. Yet, how these flowers influence pollinators' foraging choices within an inflorescence remains unclear. We hypothesised that rewardless flowers in an inflorescence may act as “decoys”, causing the rewarding flowers in the inflorescence to be perceived as more valuable by contrast. Using artificial inflorescences, we presented individual bumblebees (Bombus terrestris) with a binary choice between two equally rewarding inflorescences, one of which included additional unrewarded, differently coloured flowers. We found that the presence of rewardless flowers did not increase bees’ preference for neighbouring flowers, nor did it affect their overall choice between inflorescences. However, bees quickly learned to avoid the unrewarded flowers, drastically reducing visits and probing within a few foraging bouts. We review research on decoy effects in bees, and find very little support for their presence. Our findings contribute to the growing body of evidence that rewardless flowers do not induce decoy effects in bees, and highlight the need for further research into the ecological role of nectarless flowers within floral patches. It may be time to abandon the search for classical decoy effects in pollinators.

摘要
无花蜜花朵在被子植物中较为常见，这类植物通常会保留颜色改变的无报酬花朵，而非将其脱落。然而，这类花朵如何影响传粉者在单个花序内的觅食选择，目前仍不明确。我们提出假说：花序中的无报酬花朵可充当“诱饵（decoy）”，通过对比效应使花序内的有报酬花朵看起来更具价值。本研究使用人工花序，为每只欧洲熊蜂（Bombus terrestris）提供二元选择：在两个报酬水平完全一致的花序中进行选择，其中一个额外带有若干无报酬、颜色不同的花朵。实验结果显示，无报酬花朵的存在并未提升熊蜂对邻近花朵的偏好，也未影响其对花序的整体选择倾向。不过，熊蜂会快速学会规避无报酬花朵，在数次觅食回合内便大幅减少了对这类花朵的拜访与探查次数。我们对熊蜂相关的诱饵效应研究进行了综述，发现几乎没有证据支持这类效应的存在。本研究结果进一步丰富了相关证据，表明无报酬花朵并不会在熊蜂中诱发诱饵效应，同时强调了需要开展更多研究，以解析无花蜜花朵在花斑块中的生态功能。此时或许应当摒弃在传粉者中寻找经典诱饵效应的研究思路。