Data from: Mountain metacommunities: climate and spatial connectivity shape ant diversity in a complex landscape

Understanding what drives biodiversity patterns across scales is the central goal of ecology. Both environmental gradients and spatial landscape structure have been found to be important factors influencing species distributions and community composition, and partly reflect the balance of underlying deterministic and stochastic community processes. In some systems, environmental gradients and spatial connectivity are intertwined in that steep environmental gradients serve as boundaries on species movements and impose environment-derived complex spatial structure to metacommunities. Mountainous landscapes are prime examples of this, and recent theory has linked principles of geomorphology, environmental gradients, and spatial structure to make predictions for resulting community patterns. In this context, we examine variation in taxonomic and phylogenetic ant diversity patterns along a geographic transect spanning >5000 m in elevational range in the Hengduan mountains of southern China. We found that environmental gradients dominate variation in both alpha and beta diversity in this landscape, with alpha diversity strongly declining with elevation and beta diversity driven by elevational differences. However, within an elevational band spatial connectivity predicts beta diversity better than geographic distance. Our findings deviate from theoretical predictions in several ways, notably alpha diversity is monotonically declining and within-band beta diversity is invariant with increasing elevation. The discrepancies between theory and observation may be explained by differences in the Hengduan landscape from idealized fluvial landscapes, such as a lack of a mid-elevation peak in connectivity, as well as evolutionary limits on the source pool of species available to populate metacommunities at different elevations. The latter is supported by variation in phylogenetic community structure with elevation. Our results demonstrate the power of conceptual, statistical, and theoretical frameworks that integrate the roles of environment and spatial structure in metacommunities, but that additional work is needed to bridge the gap between abstract theory and real systems.阐明驱动不同尺度下生物多样性（biodiversity）格局形成的机制，是生态学的核心研究目标。环境梯度（environmental gradients）与空间景观结构（spatial landscape structure）均为影响物种分布（species distributions）与群落组成（community composition）的关键因素，二者在一定程度上反映了底层确定性与随机性群落过程的平衡。在部分生态系统中，环境梯度与空间连通性（spatial connectivity）相互交织：陡峭的环境梯度会限制物种迁移，并为集合群落（metacommunities）塑造源自环境的复杂空间结构。山地景观便是这类现象的典型代表，近期的理论研究将地貌学（geomorphology）、环境梯度与空间结构的相关原理相结合，对由此产生的群落格局做出了预测。基于此，我们针对中国南部横断山脉内一条跨度超过5000米海拔范围的地理样带（geographic transect），分析了蚂蚁的分类学与系统发育多样性格局的变化规律。研究发现，该景观中的α多样性（alpha diversity）与β多样性（beta diversity）变异主要受环境梯度主导：α多样性随海拔升高呈显著下降趋势，而β多样性则由海拔差异驱动。不过，在同一海拔带内，空间连通性对β多样性的预测效果优于地理距离（geographic distance）。我们的研究结果在多个方面与理论预测存在偏差：尤为突出的是，α多样性呈单调递减趋势，且同海拔带内的β多样性不随海拔升高发生变化。理论与实际观测之间的差异，可归因于横断山脉景观与理想化河流景观（fluvial landscapes）的不同特征——例如连通性不存在中海拔峰值，以及不同海拔处可供集合群落定植的物种种源库（source pool）存在进化限制。后一点得到了系统发育群落结构（phylogenetic community structure）随海拔变化的研究结果的支持。本研究证实了整合环境与空间结构作用的集合群落概念、统计与理论框架的有效性，但仍需开展更多研究以弥合抽象理论与真实生态系统之间的差距。