Data from: Is environmental legislation conserving tropical stream faunas? a large-scale assessment of local, riparian and catchment-scale influences on Amazonian stream fish

1.Agricultural expansion and intensification are major threats to tropical biodiversity. In addition to the direct removal of native vegetation, agricultural expansion often elicits other human-induced disturbances, many of which are poorly addressed by existing environmental legislation and conservation programmes. This is particularly true for tropical freshwater systems, where there is considerable uncertainty about whether a legislative focus on protecting riparian vegetation is sufficient to conserve stream fauna. 2.To assess the extent to which stream fish are being effectively conserved in agricultural landscapes, we examined the spatial distribution of assemblages in river basins to identify the relative importance of human impacts at instream, riparian, and catchment scales, in shaping observed patterns. We used an extensive dataset on the ecological condition of 83 low-order streams distributed in three river basins in the eastern Brazilian Amazon. 3.We collected and identified 24,420 individual fish from 134 species. Multiplicative diversity partitioning revealed high levels of compositional dissimilarity (DS) among stream sites (DS = 0.74 to 0.83) and river basins (DS = 0.82), due mainly to turnover (77.8 to 81.8%) rather than nestedness. The highly heterogeneous fish faunas in small Amazonian streams underscore the vital importance of enacting measures to protect forests on private lands outside of public protected areas. 4.Instream habitat features explained more variability in fish assemblages (15-19%) than riparian (2-12%), catchment (4-13%) or natural covariates (4-11%). Although grouping species into functional guilds allowed us to explain up to 31% of their abundance (i.e. for nektonic herbivores), individual riparian- and catchment-scale predictor variables that are commonly a focus of environmental legislation explained very little of the observed variation (partial R2 values mostly < 5%). 5.Policy implications. Current rates of agricultural intensification and mechanisation in tropical landscapes are unprecedented, yet the existing legislative frameworks focusing on protecting riparian vegetation seem insufficient to conserve stream environments and their fish assemblages. To safeguard the species-rich freshwater biota of small Amazonian streams, conservation actions must shift towards managing whole basins and drainage networks, as well as agricultural practices in already-cleared land.1.农业扩张与集约化是热带生物多样性面临的主要威胁。除直接清除原生植被外，农业扩张往往还会引发其他人为干扰，而现有环境立法与保护计划大多未能有效应对这些干扰。这一问题在热带淡水生态系统中尤为突出：目前学界对于仅以保护河岸植被（riparian vegetation）为立法重点是否足以保护溪流动物群（stream fauna）仍存在较大不确定性。 2.为评估农业景观中溪流鱼类的有效保护程度，本研究通过分析流域内鱼类群落的空间分布，明确了溪流尺度、河岸尺度与集水区（catchment）尺度的人为干扰在塑造观测群落格局中的相对重要性。本研究使用了巴西亚马孙东部三个流域内83条低级别溪流（low-order streams）的生态状况大型数据集。 3.本研究共采集并鉴定了134种鱼类共计24420尾个体。乘性多样性分区（Multiplicative diversity partitioning）分析显示，溪流样点间及流域间的群落组成差异（compositional dissimilarity，DS）水平较高，其中溪流样点间DS为0.74~0.83，流域间DS为0.82；这种差异主要源于物种更替（turnover，占比77.8%~81.8%）而非嵌套结构（nestedness）。亚马孙小型溪流中鱼类区系的高度异质性，凸显了在公共保护区之外制定私有林地保护措施的极端重要性。 4.溪流内生境特征对鱼类群落变异的解释度（15%~19%）高于河岸尺度（2%~12%）、集水区尺度（4%~13%）及自然协变量（4%~11%）。尽管将物种划分为功能群（functional guilds）后，可解释高达31%的鱼类丰度变异（如自游植食者nektonic herbivores），但现有环境立法通常关注的单一河岸与集水区尺度预测变量，对观测到的群落变异解释度极低（偏R²值大多小于5%）。 5.政策启示。当前热带区域的农业集约化与机械化速率史无前例，但现有以保护河岸植被为核心的立法框架，似乎不足以保护溪流生境及其鱼类群落。为保护亚马孙小型溪流中物种丰富的淡水生物区系，保护行动必须转向全流域与河网系统的管理，同时优化已开垦土地的农业生产方式。