Data from: Bumble bee nest abundance, foraging distance, and host-plant reproduction: implications for management and conservation

Recent reports of global declines in pollinator species imply an urgent need to assess the abundance of native pollinators and density-dependent benefits for linked plants. In this study, we investigated (1) pollinator nest distributions and estimated colony abundances, (2) the relationship between abundances of foraging workers and the number of nests they represent, (3) pollinator foraging ranges, and (4) the relationship between pollinator abundance and plant reproduction. We examined these questions in an alpine ecosystem in the Colorado Rocky Mountains, focusing on four alpine bumble bee species (Bombus balteatus, B. flavifrons, B. bifarius, and B. sylvicola), and two host plants that differ in their degrees of pollinator specialization (Trifolium dasyphyllum and T. parryi). Using microsatellites, we found that estimated colony abundances among Bombus species ranged from ~18 to 78 colonies/0.01 km2. The long-tongued species B. balteatus was most common, especially high above treeline, but the subalpine species B. bifarius was unexpectedly abundant for this elevation range. Nests detected among sampled foragers of each species were correlated with the number of foragers caught. Foraging ranges were smaller than expected for all Bombus species, ranging from 25 to 110 m. Fruit set for the specialized plant, Trifolium parryi, was positively related to the abundance of its Bombus pollinator. In contrast, fruit set for the generalized plant, T. dasyphyllum, was related to abundance of all Bombus species. Because forager abundance was related to nest abundance of each Bombus species and was an equally effective predictor of plant fecundity, forager inventories are probably suitable for assessing the health of outcrossing plant populations. However, nest abundance, rather than forager abundance, better reflects demographic and genetic health in populations of eusocial pollinators such as bumble bees. Development of models incorporating the parameters we have measured here (nest abundance, forager abundance, and foraging distance) could increase the usefulness of foraging worker inventories in monitoring, managing, and conserving pollinator populations.近期有关传粉者物种全球衰退的研究报道显示，亟需开展本土传粉者种群丰度评估，以及其对关联植物所提供的密度依赖性益处的相关研究。本研究围绕四大核心问题展开探究：(1) 传粉者的巢穴分布与预估种群丰度；(2) 觅食工蜂种群丰度与其所代表的巢穴数量之间的关联；(3) 传粉者的觅食范围；(4) 传粉者丰度与植物繁殖性能之间的关系。本研究于科罗拉多落基山脉的高山生态系统中开展上述探究，实验对象涵盖4种高山熊蜂属（Bombus）物种：Bombus balteatus、B. flavifrons、B. bifarius及B. sylvicola，以及2种在传粉专一性程度上存在显著差异的宿主植物：Trifolium dasyphyllum与Trifolium parryi。本研究借助微卫星（microsatellites）标记开展分析，结果显示不同熊蜂属物种的预估种群丰度介于约18至78个巢穴/0.01平方千米之间。长舌型物种B. balteatus为优势物种，尤其在林线以上的高海拔区域分布最为广泛；而亚高山物种B. bifarius在该海拔区间内的种群丰度远超预期。各物种采样觅食工蜂中检测到的巢穴数量，与捕获的工蜂个体数量呈显著正相关。所有熊蜂属物种的觅食范围均小于预期，仅为25至110米。专一性传粉植物T. parryi的坐果率，与其专属熊蜂传粉者的种群丰度呈显著正相关。与之相对，泛化传粉植物T. dasyphyllum的坐果率，则与所有熊蜂属物种的种群丰度均存在关联。由于觅食工蜂的种群丰度与各熊蜂属物种的巢穴丰度存在关联，且同样可作为植物繁殖性能的有效预测指标，因此觅食工蜂的种群调查或可用于评估异交植物种群的健康水平。但对于熊蜂这类真社会性（eusocial）传粉者种群而言，巢穴丰度相较觅食工蜂丰度，更能准确反映其种群的人口统计学与遗传健康状况。开发纳入本研究测定的各项参数（巢穴丰度、觅食工蜂丰度与觅食距离）的模型，或可提升觅食工蜂种群调查在传粉者种群监测、管理与保护工作中的应用价值。