Data from: Environmental and spatial effects on coastal stream fishes in the Atlantic rainforest

Contemporary and historical factors influence assemblage structure. The environmental and spatial influences acting on fish organization of rainforest coastal streams in the Atlantic rainforest of Brazil were examined. Fish (and functional traits such as morphology, diet, velocity preference, body size), environmental variables (pH, water conductivity, dissolved oxygen, temperature, stream width, flow, depth, substrate) and altitude were measured from 59 stream reaches. Asymmetric eigenvector maps were used to model the spatial structure considering direction of fish movements. Elevation played an important role – fish abundance, biomass, and richness all decrease with increasing elevation. Fish communities are influenced by both environmental and spatial factors, but downstream movements were shown to be more important in explaining the observed spatial variation than were bidirectional and upstream movements. Spatial factors, as well as environmental variables influenced by the spatial structure, explained most of the variation in fish assemblages. The strong spatial structuring is probably attributable to asymmetric dispersal limitation along the altitudinal profile: dispersal is likely to be more limiting moving upstream than downstream. These fish assemblages reflect scale-dependent processes: at the stream reach-scale, fish respond to local environmental filters (habitat structure, water chemistry, and food supply), which are in turn influenced by a larger scale, namely the altitudinal gradient expected in steep coastal mountains. Thus, environmental drivers are not independent of spatial factors, and the effects of local factors can be confounded across the altitudinal gradient. These results may have implications for conservation, because downstream reaches are often neglected in management and conservation plans.群落结构受到当代与历史因素的共同调控。本研究针对巴西大西洋雨林中的雨林沿海溪流，调查了环境与空间因素对鱼类群落组织的调控作用。研究人员对59个溪流河段开展了采样测定，记录了鱼类相关数据（涵盖形态、食性、流速偏好、体尺等功能性状）、环境变量（包括酸碱度、电导率、溶解氧、水温、溪流宽度、流速、水深与底质）以及海拔信息。本研究采用非对称特征向量映射（Asymmetric Eigenvector Maps），结合鱼类移动方向构建空间结构模型。结果表明，海拔发挥了显著的调控作用：鱼类丰度、生物量及物种丰富度均随海拔升高而降低。鱼类群落同时受到环境与空间因素的共同影响，但相较于双向迁移与上游迁移，下游迁移对解释观测到的空间变异的贡献更为突出。空间因素以及受空间结构调控的环境变量，能够解释鱼类群落变异的绝大部分。这种显著的空间结构大概率源于沿海拔梯度的非对称扩散限制：相较于下游方向，向上游的扩散更易受到阻碍。该鱼类群落反映了尺度依赖的生态过程：在溪流河段尺度下，鱼类响应局域环境过滤作用（包括栖息地结构、水体化学特征与食物供给），而这些局域因素又受到更大尺度的影响，即陡峭沿海山地典型的海拔梯度。由此可见，环境驱动因子并非独立于空间因素，局域因素的生态效应会在海拔梯度上产生混淆。本研究结果或可为保护工作提供参考，因为下游河段在当前的管理与保护规划中常被忽视。