Data from: Inter-assemblage facilitation: the functional diversity of cavity-producing beetles drives the size diversity of cavity-nesting bees

Inter-specific interactions are important drivers and maintainers of biodiversity. Compared to trophic and competitive interactions, the role of non-trophic facilitation among species has received less attention. Cavity-nesting bees nest in old beetle borings in dead wood, with restricted diameters corresponding to the body size of the bee species. The aim of this study was to test the hypothesis that the functional diversity of cavity-producing wood boring beetles - in terms of cavity diameters - drives the size diversity of cavity-nesting bees. The invertebrate communities were sampled in 30 sites, located in forested landscapes along an elevational gradient. We regressed the species richness and abundance of cavity nesting bees against the species richness and abundance of wood boring beetles, non-wood boring beetles and elevation. The proportion of cavity nesting bees in bee species assemblage was regressed against the species richness and abundance of wood boring beetles. We also tested the relationships between the size diversity of cavity nesting bees and wood boring beetles. The species richness and abundance of cavity nesting bees increased with the species richness and abundance of wood boring beetles. No such relationship was found for non-wood boring beetles. The abundance of wood boring beetles was also related to an increased proportion of cavity nesting bee individuals. Moreover, the size diversity of cavity-nesting bees increased with the functional diversity of wood boring beetles. Specifically, the mean and dispersion of bee body sizes increased with the functional dispersion of large wood boring beetles. The positive relationships between cavity producing bees and cavity nesting bees suggest that non-trophic facilitative interactions between species assemblages play important roles in organizing bee species assemblages. Considering a community-wide approach may therefore be required if we are to successfully understand and conserve wild bee species assemblages in forested landscapes.

种间相互作用（inter-specific interactions）是生物多样性（biodiversity）的关键驱动因子与维持机制。相较于营养级相互作用（trophic interaction）与种间竞争（competitive interaction），物种间的非营养级促进作用（non-trophic facilitation）迄今受到的学术关注仍较为有限。洞栖蜂（cavity-nesting bee）会利用朽木中甲虫蛀蚀形成的孔洞筑巢，其可利用的巢孔直径需与自身体型大小相适配。本研究旨在验证如下假说：以蛀木甲虫（wood boring beetle）所产孔洞的直径维度为衡量标准，产洞蛀木甲虫的功能多样性（functional diversity）会驱动洞栖蜂的体型多样性（size diversity）。我们沿海拔梯度（elevational gradient）在森林景观内布设了30个采样点，对样地内的无脊椎动物群落（invertebrate community）开展了系统采样。随后，我们以洞栖蜂的物种丰富度（species richness）与个体丰度（abundance）为因变量，以蛀木甲虫、非蛀木甲虫的物种丰富度与个体丰度以及海拔为自变量开展回归分析。同时，我们还针对蜂类群落组成中洞栖蜂的占比，以蛀木甲虫的物种丰富度与个体丰度为自变量开展了回归分析。此外，我们还检验了洞栖蜂的体型多样性与蛀木甲虫之间的关联关系。研究结果显示，洞栖蜂的物种丰富度与个体丰度会随蛀木甲虫的物种丰富度与个体丰度的升高而显著增加，而非蛀木甲虫则未呈现此类相关性。蛀木甲虫的个体丰度同样与洞栖蜂个体在蜂类群落中的占比提升存在显著正相关。进一步分析表明，洞栖蜂的体型多样性会随蛀木甲虫的功能多样性升高而提升；具体而言，蜂类体型的平均值与离散程度会随大型蛀木甲虫的功能离散度（functional dispersion）的增大而升高。蛀木甲虫与洞栖蜂之间的正向关联表明，不同物种类群间的非营养级促进作用在调控蜂类群落的构建过程中发挥了重要作用。因此，若要充分理解并保护森林景观中的野生蜂类群落，或许需要采用群落水平的研究视角。