Bronstein Judith L, Davidowitz Goggy, Lichtenberg Elinor M, Irwin Rebecca E
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA.
Department of Entomology, University of Arizona, Tucson, AZ 85721, USA.
Plants (Basel). 2024 Sep 6;13(17):2507. doi: 10.3390/plants13172507.
Primary nectar-robbers feed through holes they make in flowers, often bypassing the plant's reproductive organs in the process. In many robbed plants, multiple holes are made in a single flower. Why a flower should be robbed repeatedly is difficult to understand: a hole signals that a nectar forager has already fed, which would seem likely to predict low rewards. We tested three explanations for this pattern in (Fumariaceae), a bumble bee pollinated and robbed plant: (1) multiple holes appear only after all flowers have been robbed once; (2) individual foragers make multiple holes during single visits; and (3) it is more profitable for bees to rob older flowers, even if they have already been robbed. We tested these hypotheses from 2014 to 2016 in a Colorado, USA population using data on robbing rates over time, floral longevity, nectar accumulation in visited and unvisited flowers, and the accumulation of robbing holes across the life of flowers. Multiple holes were already appearing when two-thirds of flowers still lacked a single hole, allowing us to reject the first hypothesis. The second hypothesis cannot offer a full explanation for multiple robbing holes because 35% of additional holes appeared in flowers one or more days after the first hole was made. Repeated sampling of bagged and exposed inflorescences revealed that flowers filled at a constant rate and refilled completely after being drained. Consequently, young flowers are of consistently low value to foragers compared to older flowers even if they had previously been robbed, consistent with the third hypothesis. While further studies are needed, these results offer a simple explanation for the paradoxical clustering of nectar-robbing damage in this and possibly other plant species.
初级花蜜盗窃者通过它们在花朵上制造的洞来获取花蜜，在此过程中常常绕过植物的生殖器官。在许多被盗的植物中，一朵花上会出现多个洞。一朵花为何会被反复盗窃，这很难理解：一个洞表明有一个花蜜觅食者已经取食过了，这似乎预示着回报很低。我们针对紫堇科的一种植物（由熊蜂授粉且会被盗蜜），对这种模式的三种解释进行了测试：（1）只有在所有花朵都被盗窃过一次之后才会出现多个洞；（2）单个觅食者在单次访问期间会制造多个洞；（3）对蜜蜂来说，盗窃较老的花朵更有利可图，即使这些花已经被盗窃过。我们在2014年至2016年期间，利用美国科罗拉多州一个种群中随时间变化的盗蜜率、花的寿命、被访问和未被访问花朵中的花蜜积累情况以及花朵一生中盗洞积累的数据，对这些假设进行了测试。当仍有三分之二的花朵连一个洞都没有时，就已经出现了多个洞，这使我们能够否定第一个假设。第二个假设无法对多个盗洞做出全面解释，因为35%的额外洞出现在第一个洞形成后的一天或多天后的花朵上。对套袋和未套袋花序的重复采样表明，花朵以恒定速率填充，排空后会完全重新填满。因此，与较老的花朵相比，即使较年轻的花朵之前被盗过，对觅食者来说其价值始终较低，这与第三个假设一致。尽管还需要进一步研究，但这些结果为这种以及可能其他植物物种中花蜜盗窃损害的矛盾聚集现象提供了一个简单的解释。
