Patterns of insect diversity along elevational gradients are well described in ecology. However, it remains little tested how variation in the quantity, quality, and diversity of food resources influence these patterns. Here we analyzed the direct and indirect effects of climate, food quantity (estimated by net primary productivity), quality (variation in the specific leaf area index, leaf nitrogen to phosphorus and leaf carbon to nitrogen ratio), and food diversity (diversity of leaf traits) on the species richness of phytophagous beetles along the broad elevation and land use gradients of Mt. Kilimanjaro, Tanzania. We sampled beetles at 65 study sites located in both natural and anthropogenic habitats, ranging from 866 to 4,550 m asl. We used path analysis to unravel the direct and indirect effects of predictor variables on species richness. In total, 3,154 phytophagous beetles representing 19 families and 304 morphospecies were collected. We found that the species richness of phytophagous beetles was bimodally distributed along the elevation gradient with peaks at the lowest (˜866 m asl) and upper mid-elevations (˜3,200 m asl) and sharply declined at higher elevations. Path analysis revealed temperature- and climate-driven changes in primary productivity and leaf trait diversity to be the best predictors of changes in the species richness of phytophagous beetles. Species richness increased with increases in mean annual temperature, primary productivity, and with increases in the diversity of leaf traits of local ecosystems. Our study demonstrates that, apart from temperature, the quantity and diversity of food resources play a major role in shaping diversity gradients of phytophagous insects. Drivers of global change, leading to a change of leaf traits and causing reductions in plant diversity and productivity, may consequently reduce the diversity of herbivore assemblages.

中文翻译：

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植物性状介导气候对乞力马扎罗山植食性甲虫多样性的影响

生态学中很好地描述了沿海拔梯度的昆虫多样性模式。然而，很少有人测试食物资源的数量、质量和多样性如何影响这些模式。在这里，我们分析了气候、食物数量（由净初级生产力估计）、质量（特定叶面积指数、叶氮磷和叶碳氮比的变化）和食物多样性（叶的多样性）的直接和间接影响。性状）对坦桑尼亚乞力马扎罗山宽阔海拔和土地利用梯度上的植食性甲虫物种丰富度的影响。我们在位于自然和人为栖息地的 65 个研究地点对甲虫进行了采样，范围从 866 米到 4,550 米不等。我们使用路径分析来阐明预测变量对物种丰富度的直接和间接影响。总共收集了代表 19 个科和 304 个形态种的 3,154 只植食性甲虫。我们发现植食性甲虫的物种丰富度沿海拔梯度呈双峰分布，峰值出现在最低海拔 (~866 m asl) 和中高海拔 (~3,200 m asl) 处，在较高海拔处急剧下降。路径分析显示，温度和气候驱动的初级生产力和叶片性状多样性变化是食草甲虫物种丰富度变化的最佳预测因子。物种丰富度随着年平均温度和初级生产力的增加以及当地生态系统叶片性状多样性的增加而增加。我们的研究表明，除了温度，食物资源的数量和多样性在塑造植食性昆虫的多样性梯度方面发挥着重要作用。全球变化的驱动因素，导致叶片性状发生变化并导致植物多样性和生产力下降，可能因此减少食草动物组合的多样性。