Understanding whether pollinator behaviors and species richness drive crop yields is a key area of investigation in pollination ecology. Using sunflower as a study species we describe variation in mean floral visitation times among bee taxa and test how interactions between bee richness and the proportion of bumblebees in localized communities impact seed yield. Seven bee genera commonly visited sunflower including Agapostemon, Bombus, Halictus, Lasioglossum, Megachile, Melissodes, and Svastra. Mean visitation times to sunflower varied across genera and Bombus and Halictus spp. spent the most time foraging on inflorescences, but the number of visits by Bombus spp. was the only parameter associated with increased yields. Experimental pollination deficit reduced seed development and yields, and these effects were stronger in stands of wild-type sunflower in the field compared to a confection variety grown in the greenhouse. Relationships between bee richness and pollination services differed for potted and wild sunflower: when bees had short-term access to potted sunflower, bee richness and relative Bombus abundances were not associated with pollination quotients. When bees had long-term access to wild sunflower, relative Bombus abundances predicted pollination services but were modified by site-level bee richness: as richness increased, the effects of Bombus abundance decreased. Our studies demonstrate that bee species richness is not always a clear predictor of pollination services; instead, our results underscore the importance of specific taxa when species richness is low (here, bumblebees), and show that the effects of bee functional groups important for pollination may be modified by changes in site-level species richness.

中文翻译：

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大黄蜂（膜翅目：蜜蜂科）访问频率驱动种子产量并与站点级物种丰富度相互作用以推动向日葵的授粉服务

了解授粉者行为和物种丰富度是否会推动作物产量是授粉生态学研究的一个关键领域。使用向日葵作为研究物种，我们描述了蜜蜂类群中平均花卉访问时间的变化，并测试了蜜蜂丰富度与本地群落中大黄蜂比例之间的相互作用如何影响种子产量。向日葵有七种常见的蜜蜂属，包括 Agapostemon、Bombus、Halictus、Lasioglossum、Megachile、Melissodes 和 Svastra。向日葵的平均访问时间因属、熊蜂和哈利克图斯属而异。在花序上觅食的时间最多，但熊蜂的访问次数。是与产量增加相关的唯一参数。实验性授粉不足降低了种子发育和产量，与在温室中种植的糖果品种相比，这些效果在田间野生型向日葵的林分中更强。盆栽和野生向日葵的蜜蜂丰富度和授粉服务之间的关系不同：当蜜蜂短期接触盆栽向日葵时，蜜蜂丰富度和相对熊蜂丰度与授粉商无关。当蜜蜂长期接触野生向日葵时，Bombus 的相对丰度可以预测授粉服务，但会受到现场蜜蜂丰富度的影响：随着丰富度的增加，Bombus 丰度的影响会降低。我们的研究表明，蜜蜂物种丰富度并不总是能明确预测授粉服务；相反，我们的结果强调了当物种丰富度较低时特定分类群的重要性（这里是大黄蜂），