Data from: Patterns of size variation in bees at a continental scale: does Bergmann’s rule apply?

Body size latitudinal clines have been widley explained by the Bergmann’s rule in homeothermic vertebrates. However, there is no general consensus in poikilotherms organisms in particular in insects that represent the large majority of wildlife. Among them, bees are a highly diverse pollinators group with high economic and ecological value. Nevertheless, no comprehensive studies of species assemblages at a phylogenetically larger scale have been carried out even if they could identify the traits and the ecological conditions that generate different patterns of latitudinal size variation. We aimed to test Bergmann’s rule for wild bees by assessing relationships between body size and latitude at continental and community levels. We tested our hypotheses for bees showing different life history traits (i.e. sociality and nesting behaviour). We used 142,008 distribution records of 615 bee species at 50 km x 50 km (CGRS) grids across the West Palearctic. We then applied Generalized Least Squares fitted linear model (GLS) to assess the relationship between latitude and mean body size of bees, taking into account spatial autocorrelation. For all bee species grouped, mean body size increased with higher latitudes, and so followed Bergmann’s rule. However, considering bee genera separately, four genera were consistent with Bergmann’s rule, while three showed a converse trend, and three showed no significant cline. All life history traits used here (i.e. solitary, social and parasitic behaviour; ground and stem nesting behaviour) displayed a Bergmann’s cline. In general there is a main trend for larger bees in colder habitats, which is likely to be related to their thermoregulatory abilities and partial endothermy, even if a “season length effect” (i.e. shorter foraging season) is a potential driver of the converse Bergmann’s cline particularly in bumblebees.恒温脊椎动物的体型纬度梯度格局长期以来均以伯格曼法则（Bergmann’s Rule）进行解释。然而，变温动物（poikilotherms）类群对此尚未形成普遍共识，尤以占野生动物绝大多数的昆虫类群为甚。其中，蜂类是物种多样性极高的传粉类群，兼具重要的经济与生态价值。尽管此类研究能够揭示驱动体型纬度分布格局差异的功能性状与生态条件，但此前尚未开展过系统发育尺度更大的蜂类物种组合综合性研究。本研究旨在通过在大陆与群落两个尺度上分析体型与纬度的关联，验证野生蜂类的伯格曼法则适用性，并针对具备不同生活史性状（即社会性行为与筑巢行为）的蜂类开展假设检验。本研究使用了西古北界（West Palearctic）范围内50km×50km（CGRS）网格下的615种蜂类的142008条分布记录。随后，我们采用考虑空间自相关（spatial autocorrelation）的广义最小二乘线性模型（Generalized Least Squares, GLS），分析纬度与蜂类平均体型之间的关联。当所有蜂类合并分析时，平均体型随纬度升高而增大，符合伯格曼法则。但分属分析时，有4个属的蜂类符合伯格曼法则，3个属呈现相反趋势，另有3个属未表现出显著的纬度梯度格局。本研究涉及的所有生活史性状（即独居、社会与寄生行为；地表筑巢与茎秆筑巢行为）均呈现出伯格曼型纬度梯度。总体而言，寒冷生境中的蜂类体型更大，这可能与其体温调节能力以及部分内温性相关；不过“季节长度效应”（即觅食季更短）可能是部分类群（尤其是熊蜂属）出现反伯格曼格局的潜在驱动因素。