Bee pollinators are key components of terrestrial ecosystems. Evidence is mounting that bees are globally in decline, and species with a higher degree of specialization are the most vulnerable to local extinction. However, ecological features that could explain bee specialization remain poorly tested, especially in tropical species. Here, we aim to determine the most specialized bee species and their associated ecological traits in tropical bee-plant interaction networks, answering three questions: (1) Which bees in the interaction networks are specialists? (2) Is body size related to their role as specialists in interaction networks? (3) Are there phylogenetic relationships between the bee species identified as specialists? We used fifteen quantitative plant-bee interaction networks from different Brazilian biomes covering 1,702 interactions (386 bee and 717 plant species). We used the normalized degree (standardized number of partners) as a metric to determine trophic specialization of bee species. Body size was estimated by measuring intertegular distance (ITD), i.e. the distance between the bases of the wings on the thorax. Evolutionary distinctiveness (ED) was used to quantify species uniqueness, i.e. the singularity of species’ genomes and functions within the clade. Relationships between dietary specialism, ITD and ED were assessed using generalized linear models. We detected 34 specialist bee species (9% of total species), distributed in 13 genera, and four families. ITD and ED were important variables explaining the specialization of tropical bee species. Specialists were larger and less phylogenetically distinct than expected by chance. Based on a large data set covering some of the main tropical biomes, our results suggest that loss of specialist bees from Brazilian bee-plant networks could have deleterious consequences for native plant species exclusively pollinated by large-bodied bees. Moreover, by affecting more evolutionarily distinct species, i.e. those with fewer extant relatives, the loss of specialist bees will likely affect few clades but can result on considerable loss of evolutionary history and phylogenetic diversity in the Brazilian bee communities. The results are important for decision-making concerning conservation measures for these species and may also encourage the development of sustainable management techniques for bees.

中文翻译：

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与热带植物 - 蜜蜂相互作用网络中的通才相比，专业蜜蜂物种更大，在系统发育上的差异更小

蜜蜂传粉者是陆地生态系统的关键组成部分。越来越多的证据表明，蜜蜂在全球范围内正在减少，专业化程度更高的物种最容易在当地灭绝。然而，可以解释蜜蜂专业化的生态特征仍然缺乏测试，特别是在热带物种中。在这里，我们的目标是确定热带蜂-植物相互作用网络中最专业的蜜蜂物种及其相关的生态特征，回答三个问题：（1）相互作用网络中的哪些蜜蜂是专家？(2) 体型与他们作为互动网络专家的角色有关吗？(3) 鉴定为专家的蜜蜂物种之间是否存在系统发育关系？我们使用了来自巴西不同生物群落的 15 个定量植物-蜜蜂相互作用网络，涵盖 1、702 种相互作用（386 种蜜蜂和 717 种植物）。我们使用标准化程度（合作伙伴的标准化数量）作为衡量蜜蜂物种营养专业化的指标。体型是通过测量跨距（ITD）来估计的，即胸部翅膀基部之间的距离。进化独特性 (ED) 被用来量化物种的独特性，即物种基因组和进化枝内功能的奇异性。饮食专长、ITD 和 ED 之间的关系使用广义线性模型进行评估。我们检测到 34 种专业蜜蜂（占总种数的 9%），分布在 13 个属和 4 个科。ITD 和 ED 是解释热带蜜蜂物种专业化的重要变量。专家比偶然预期的更大，在系统发育上的差异更小。基于涵盖一些主要热带生物群落的大型数据集，我们的结果表明，巴西蜜蜂植物网络中专业蜜蜂的消失可能会对仅由大型蜜蜂授粉的本地植物物种产生有害后果。此外，通过影响更多进化上不同的物种，即那些现存亲属较少的物种，专业蜜蜂的丧失可能会影响很少的进化枝，但可能导致巴西蜜蜂群落的进化历史和系统发育多样性的显着丧失。结果对于有关这些物种保护措施的决策很重要，也可能鼓励开发蜜蜂的可持续管理技术。我们的结果表明，巴西蜜蜂植物网络中专业蜜蜂的消失可能会对仅由大型蜜蜂授粉的本地植物物种产生有害后果。此外，通过影响更多进化上不同的物种，即那些现存亲属较少的物种，专业蜜蜂的丧失可能会影响很少的进化枝，但可能导致巴西蜜蜂群落的进化历史和系统发育多样性的显着丧失。结果对于有关这些物种保护措施的决策很重要，也可能鼓励开发蜜蜂的可持续管理技术。我们的结果表明，巴西蜜蜂植物网络中专业蜜蜂的消失可能会对仅由大型蜜蜂授粉的本地植物物种产生有害后果。此外，通过影响更多进化上不同的物种，即那些现存亲属较少的物种，专业蜜蜂的丧失可能会影响很少的进化枝，但可能导致巴西蜜蜂群落的进化历史和系统发育多样性的显着丧失。结果对于有关这些物种保护措施的决策很重要，也可能鼓励开发蜜蜂的可持续管理技术。专业蜜蜂的消失可能会影响很少的进化枝，但可能导致巴西蜜蜂群落的进化历史和系统发育多样性的大量丧失。结果对于有关这些物种保护措施的决策很重要，也可能鼓励开发蜜蜂的可持续管理技术。专业蜜蜂的消失可能会影响很少的进化枝，但可能导致巴西蜜蜂群落的进化历史和系统发育多样性的大量丧失。结果对于有关这些物种保护措施的决策很重要，也可能鼓励开发蜜蜂的可持续管理技术。