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.当代与历史因素共同影响生物群落结构。本研究针对巴西大西洋雨林内的雨林沿海溪流，探究了作用于鱼类群落组织的环境与空间影响因子。研究人员对59个溪流河段开展调查，测定了鱼类相关指标（包括形态、食性、流速偏好、体大小等功能性状（functional traits)）、环境变量（酸碱度、水电导率、溶解氧、水温、溪流宽度、流速、水深、底质）以及海拔。研究采用不对称特征向量图（asymmetric eigenvector maps），结合鱼类移动方向对空间结构进行建模。海拔发挥了重要作用：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子的调控，但相较于双向移动与逆流移动，顺流移动在解释观测到的空间变异中更为关键。空间因子以及受空间结构影响的环境变量，解释了鱼类群落结构的绝大部分变异。这种显著的空间结构大概率归因于沿海拔梯度的不对称扩散限制：逆流移动的扩散限制大概率强于顺流移动。这些鱼类群落反映了尺度依赖的生态过程：在溪流河段尺度上，鱼类响应局域环境过滤作用（栖息地结构、水化学特征与食物供给），而这些局域因子又受到更大尺度的调控，即陡峭沿海山地的海拔梯度。因此，环境驱动因子并非独立于空间因素，且局域因子的效应会沿海拔梯度产生混淆。本研究结果或对保护工作具有启示意义，因为顺流河段在管理与保护计划中常被忽视。