Data from: Aquatic community structure across an Andes-to-Amazon fluvial gradient

Aim: Little is known about factors affecting the elevational and longitudinal zonation of tropical Andean stream communities. We investigated epilithon, macroinvertebrate and fish assemblages along a 4100-m elevational–longitudinal gradient in an Andean headwater of the Amazon Basin. We interpret our results within the context of environmental factors, emphasizing temperature, as well as ecological theory relating shifts in metazoan functional feeding groups to shifts in basal resources along the fluvial continuum. Location: Arazá-Inambari-Madre de Dios watershed, south-eastern Peru. Methods: We sampled water physicochemistry, epilithon and macroinvertebrate diversity and abundance, and fish diversity at 18 main-stem and 14 tributary sites from high puna grasslands (4300 m a.s.l.) to Amazon Basin lowlands (200 m a.s.l.). Results: Water physicochemical parameters and the taxonomic and ecological structure of invertebrate and fish assemblages displayed mostly nonlinear responses to elevation: water temperature and percentage of macroinvertebrate taxa identified as leaf shredders had U-shaped responses; dissolved oxygen and percentage of macroinvertebrate taxa identified as grazers had hump-shaped responses. Epilithon richness increased slightly with elevation whereas macroinvertebrate and fish richness decreased. Main conclusions: Elevational gradients in physicochemical parameters are insufficient to explain abrupt and nonlinear shifts in community taxonomic and functional structure. Rather, trophic interactions, including predation and longitudinal turnover in basal food resources, seem to exert a stronger influence on the distributions of Andean aquatic organisms. A steep elevational decline in relative taxonomic diversity of leaf-shredding (versus algae-grazing) insects supports the hypothesis that temperature affects the functional composition of insect assemblages via its influence on microbial decomposition rates. This relationship, and the distributions of several insect and fish species across narrow elevational bands, suggests that Andean stream communities may be sensitive to global warming. Placer mining and road building impacts have already altered stream community structure, including the absence of many benthic species from low-elevation habitats.研究目的：目前针对热带安第斯溪流群落沿海拔与经度分带的影响因素，相关研究仍较为匮乏。我们针对亚马孙流域一处安第斯源头溪流中，沿跨度达4100米的海拔-纵向梯度分布的石面着生生物（epilithon）、大型底栖无脊椎动物（macroinvertebrate）与鱼类群落展开调查，并结合环境因素（重点关注水温）以及有关后生动物功能摄食类群随河流连续体（fluvial continuum）上基础资源变化的生态学理论，对研究结果进行阐释。 研究地点：秘鲁东南部阿拉萨-因班巴里-马德雷德迪奥斯流域（Arazá-Inambari-Madre de Dios watershed）。 研究方法：我们在18个干流样点与14个支流样点开展采样，采样范围覆盖从高海拔普纳草原（4300米a.s.l.）至亚马孙流域低地（200米a.s.l.）的区域，采样内容包括水体理化性质、石面着生生物、大型底栖无脊椎动物的多样性与丰度，以及鱼类多样性。 研究结果：水体理化参数以及无脊椎动物与鱼类群落的分类学、生态学结构整体呈现出对海拔的非线性响应：水温和被鉴定为碎叶类群的大型无脊椎动物类群占比呈U型响应；溶解氧与被鉴定为刮食类群的大型无脊椎动物类群占比呈驼峰型响应。石面着生生物的物种丰富度随海拔升高略有上升，而大型底栖无脊椎动物与鱼类的物种丰富度则随海拔升高呈下降趋势。 主要结论：水体理化参数的海拔梯度变化，不足以解释群落分类学与功能结构所出现的突变性非线性变化。反之，营养级相互作用——包括捕食作用以及基础食物资源沿河流纵向的周转——似乎对安第斯水生生物的分布具有更强的调控作用。碎食性昆虫（相较于藻食性昆虫）的相对分类多样性随海拔升高呈显著下降趋势，这一结果支持了如下假说：水温通过影响微生物分解速率，进而调控昆虫群落的功能组成。这一关联，以及多种昆虫与鱼类物种仅分布于狭窄海拔区间的分布格局，均表明安第斯溪流群落可能对全球变暖较为敏感。砂矿开采与道路建设的干扰已对溪流群落结构造成改变，具体表现为低海拔生境中已缺失多种底栖物种。