Data from: Heterogeneous patterns of abundance of epigeic arthropod taxa along a major elevation gradient

Species diversity is the variable most commonly studied in recent ecological research. Ecological processes, however, are driven by individuals and affected by their abundances. Understanding the variation in animal abundances along climatic gradients is important for predicting changes in ecosystem processes under global warming. High abundances make arthropods, despite their small body sizes, important actors in food webs, yet abundance distributions of major arthropod taxa along climatic gradients remain poorly documented. We sampled arthropod assemblages in disturbed and undisturbed vegetation types along an elevational gradient of 860–4550 m asl on the southern slopes of Mt. Kilimanjaro, Tanzania. In our analysis, we focused on 13 taxa of arthropods that represented three major functional groups: predators, herbivores, and decomposers. Abundance patterns were unimodal for most of the taxa and functional groups, including decomposer arthropods, and most of them peaked at low elevations in lower montane forest. When we assigned beetles to functional groups, however, decomposer beetle abundances declined almost linearly, and abundances of predator beetles (ca. 2400 m asl) and herbivore beetles (ca. 3000 m asl, undisturbed vegetation) peaked at higher elevations and exhibited unimodal patterns. Temperature, not primary productivity, was the best predictor of abundance for most of the taxa and groups. Disturbance was only of minor importance. Our results revealed different trends in the response of arthropod abundance along the elevational gradient that depended on the level of taxonomic and functional resolution. This highlights the need for more comparisons of different taxa along the same climatic gradients.

物种多样性（Species diversity）是近年来生态学研究中最为常见的研究变量。然而，生态过程由个体所驱动，并受其多度的调控。明晰动物多度沿气候梯度（climatic gradients）的变化规律，对于预测全球变暖背景下生态系统过程的演变至关重要。尽管节肢动物（arthropods）体型微小，但高多度使其成为食物网（food webs）中的关键参与者；然而主流节肢动物类群沿气候梯度（climatic gradients）的多度分布仍未得到充分记录。我们于坦桑尼亚乞力马扎罗山南坡，沿860–4550米海拔（above sea level，asl）的海拔梯度（elevational gradient），对受干扰与未干扰的植被类型中的节肢动物群落（arthropod assemblages）进行了采样。本分析聚焦于代表三大主要功能群（functional groups）——捕食者、植食者与分解者的13类节肢动物。多数类群与功能群（包括分解者节肢动物）的多度格局呈单峰型，且大多在低海拔的下部山地森林达到多度峰值。但若将甲虫（beetles）按功能群划分，分解者甲虫的多度几乎呈线性下降趋势；而捕食性甲虫（约2400米海拔）与植食性甲虫（未干扰植被下约3000米海拔）的多度则在更高海拔处达到峰值，且呈单峰分布格局。对于多数类群与功能群而言，温度而非初级生产力（primary productivity）是解释多度变化的最佳预测因子；干扰的影响仅占次要地位。本研究结果揭示，节肢动物多度沿海拔梯度（elevational gradient）的响应趋势因分类学与功能分辨率的层级不同而存在差异，这凸显了在同一气候梯度（climatic gradients）下开展不同类群对比研究的必要性。