Aquatic food webs in tropical rivers are affected by spatial and temporal variations in basal resources and the composition of consumer assemblages. We used stable isotope analysis to estimate seasonal variation in basal resources supporting fish biomass in zones along the longitudinal gradient of the Usumacinta River Basin, the largest of Mesoamerica. A Bayesian isotope mixing model was used to estimate the proportional contributions of six basal resources: seston, filamentous algae, periphyton, aquatic macrophytes, riparian C3 plants and C4 plants. Models estimated that fish in the upper zone were largely supported by periphyton and riparian C3 plants during the dry season and by filamentous algae during the wet season. In the dry season, fishes in the middle and lower zones assimilated material derived from seston and, to a lesser extent, periphyton, whereas aquatic macrophytes were more important during the wet season. Chlorophyll-a measurements from the middle and lower zones suggested that seston contained large fractions of suspended algae. These patterns are consistent with the river wave concept, which predicts flow-associated changes in contributions of basal resources to the aquatic food web. The findings of this study reinforce the major role of flow regime in the ecological dynamics of rivers and how these dynamics vary depending on location and local conditions within fluvial networks.

中文翻译：

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支持墨西哥南部乌苏马辛塔河流域纵向带鱼类生物量的基础资源的季节性变化

热带河流中的水生食物网受到基础资源和消费者组合构成的时空变化的影响。我们使用稳定同位素分析来估计支持中美洲最大的乌苏马辛塔河流域纵向梯度区域中鱼类生物量的基础资源的季节性变化。贝叶斯同位素混合模型用于估计六种基础资源的比例贡献：seston、丝状藻类、附生生物、水生大型植物、河岸 C3 植物和 C4 植物。模型估计，上部区域的鱼类在旱季主要由附生生物和河岸 C3 植物支持，在雨季则由丝状藻类支持。在旱季，中低带​​的鱼类同化了来自 seston 的物质，在较小程度上，附生植物，而水生大型植物在雨季更为重要。来自中部和下部区域的叶绿素 a 测量结果表明，seston 含有大量悬浮藻类。这些模式与河流波浪概念一致，该概念预测基础资源对水生食物网的贡献与流量相关的变化。本研究的结果强调了流态在河流生态动态中的主要作用，以及这些动态如何根据河流网络中的位置和当地条件而变化。它预测了基础资源对水生食物网贡献的流量相关变化。本研究的结果强调了流态在河流生态动态中的主要作用，以及这些动态如何根据河流网络中的位置和当地条件而变化。它预测了基础资源对水生食物网贡献的流量相关变化。本研究的结果强调了流态在河流生态动态中的主要作用，以及这些动态如何根据河流网络中的位置和当地条件而变化。