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.

全球传粉者物种衰退的最新报道，凸显了评估本土传粉者种群丰度、并探究其对关联植物的密度依赖效应的迫切需求。本研究围绕四大核心问题展开：(1) 传粉者的巢穴分布与预估蜂群丰度；(2) 觅食工蜂的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成功率的关系。本研究于科罗拉多落基山脉的高山生态系统中开展，聚焦4种高山熊蜂属（Bombus）物种：白尾熊蜂（Bombus balteatus）、黄脸熊蜂（Bombus flavifrons）、二色熊蜂（Bombus bifarius）以及林生熊蜂（Bombus sylvicola），同时选取2种传粉依赖程度存在差异的宿主植物：薄叶车轴草（Trifolium dasyphyllum）与帕里车轴草（Trifolium parryi）。本研究利用微卫星标记（microsatellites）开展分析，结果显示不同熊蜂物种的预估蜂群丰度介于18~78个巢穴/0.01平方千米之间。长舌蜂种白尾熊蜂的种群最为丰富，尤其在林线以上的高海拔区域；而亚高山物种二色熊蜂在该海拔区间内的丰度却超出预期。各物种采样觅食工蜂中检测到的巢穴数量，与捕获的工蜂总数呈显著相关。所有熊蜂物种的觅食范围均低于此前预期，仅为25~110米。专性传粉植物帕里车轴草的坐果率，与其专属熊蜂传粉者的丰度呈正相关；与之相反，泛性传粉植物薄叶车轴草的坐果率，则与所有熊蜂物种的丰度均存在关联。由于觅食工蜂的丰度与各熊蜂物种的巢穴丰度存在关联，且同样可有效预测植物繁殖力，因此工蜂采样调查或可用于评估异交植物种群的健康状态。但对于熊蜂这类真社会性传粉者种群而言，巢穴丰度相较于工蜂丰度，更能准确反映其种群统计与遗传健康状况。整合本研究测得的各项参数（巢穴丰度、工蜂丰度与觅食距离）的模型开发，将有助于提升工蜂采样调查在传粉者种群监测、管理与保护工作中的应用价值。