Effect of land use on mayfly assemblages structure in Neotropical headwater streams

The aim of this study was to test the effect of agricultural and forestry land use on the structure of mayfly assemblages in low-order streams. Twenty-nine headwater streams were investigated in the state of São Paulo. We analyzed 15 streams in pristine areas (mixed tropical rainforest, semideciduous forest and dense tropical rainforest), and 14 streams covered with sugarcane, eucalyptus and pasture. Mayfly richness obtained by rarefaction curves was higher in pristine areas (21 genera), especially in mixed and semideciduous forest when compared to land use (9 genera), where values were particularly low in sugarcane plantation (3 genera). The non-metric multidimensional scaling (NMDS) ordination showed clear difference in mayfly assemblages between land uses and pristine areas, supported by analysis of similarity (R=0.67, p=0.001). In partial redundancy analysis (pRDA), the environmental descriptors that best explained differences in assemblage structure were Riparian, Channel and Environmental Inventory (RCE) index score, percentage of fine sediment stream substrate, water pH and land elevation. Our results show that agricultural and forestry land use has a strong negative effect on the structure of mayfly assemblages. These results also support the use of mayflies as environmental indicators, as some genera were sensitive to changes in land use, while others responded to naturally occurring changes in the study area.本研究旨在探究农林土地利用对低序级溪流中蜉蝣群落结构的影响。研究于圣保罗州范围内开展，共调查29条源头溪流。其中，原生自然区域（涵盖混合热带雨林、半落叶林与致密热带雨林）内的15条溪流，以及被甘蔗、桉树与牧场覆盖的14条溪流均纳入分析。通过稀疏化曲线（rarefaction curves）测得的蜉蝣物种丰富度在原生区域更高（21属），其中混合林与半落叶林的丰富度尤为突出；而受人类土地利用影响的溪流蜉蝣丰富度仅为9属，其中甘蔗种植区的数值最低，仅3属。非度量多维尺度排序（NMDS）结果显示，土地利用区域与原生区域的蜉蝣群落结构存在显著分异，相似性分析（R=0.67，p=0.001）验证了这一结果。在偏冗余分析（pRDA）中，最能解释群落结构差异的环境指标包括河岸-河道-环境清单（Riparian, Channel and Environmental Inventory, RCE）指数评分、溪流底质细颗粒沉积物占比、水体pH值以及地面海拔。本研究结果表明，农林土地利用对蜉蝣群落结构具有显著的负向影响。此外，本研究结果同样支持蜉蝣可作为环境指示生物的结论：部分蜉蝣属对土地利用变化敏感，而另一些类群则对研究区域内的自然环境变化产生响应。