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）是近年生态学研究中最常被探究的变量。然而，生态过程由个体驱动，并受其种群丰度的影响。理解动物丰度沿气候梯度（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，但较高的种群丰度使其成为食物网中的关键参与者，然而沿气候梯度分布的主要节肢动物类群的丰度分布仍鲜有记载。我们在坦桑尼亚（Tanzania）乞力马扎罗山（Mt. Kilimanjaro）南坡，沿860–4550米海拔（asl，above sea level）梯度（elevational gradient）的受干扰与未干扰植被类型中开展了节肢动物群落采样。在本次分析中，我们聚焦于代表三大主要功能群（functional groups）的13类节肢动物：捕食者、植食者与分解者。多数类群与功能群（包括分解者节肢动物）的丰度分布呈单峰模式，且大多在低海拔的下部山地森林达到丰度峰值。然而，当将甲虫（beetles）按功能群划分时，分解者甲虫的丰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（约3000米海拔，未干扰植被）的丰度则在更高海拔达到峰值，并呈现单峰分布模式。对于多数类群与功能群而言，温度而非初级生产力（primary productivity）是解释丰度变化的最佳预测因子。人为干扰的影响仅占次要地位。我们的研究结果显示，沿海拔梯度的节肢动物丰度响应趋势存在显著差异，这取决于分类学与功能学分辨率的层级。这一发现凸显了在同一气候梯度下开展不同类群对比研究的必要性。