Floodplain aquatic ecosystems experience temporal changes in basal production sources and inputs from allochthonous sources that influence energy flow. We analyzed stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) from 449 fish muscles representing 18 species to characterize energy pathways in two rivers of the lower Okavango Delta, Botswana. We sampled fish during wet and dry seasons and used mixing models to estimate proportions of major basal production sources assimilated by fishes. We estimated trophic position (TP) for each fish population and assessed the association between TP and the degree that fish biomass was supported by a single production source. During the wet season, fishes in the Boteti River assimilated material through food chains originating mainly from aquatic macrophytes. During the dry season, terrestrial C₃ plants and terrestrial C₄ grasses assumed greater importance. In the Boro River, terrestrial C₃ plants were inferred to be an important production source supporting fishes during the wet season, with aquatic macrophytes becoming more important during the dry season. In both rivers and seasons, the degree of dependence on a single source was negatively related to TP, supporting the hypothesis that organisms positioned higher in the food web tend to be supported by multiple food chains and basal sources, whereas organisms lower in the food web may be supported by many or few food chains. We showed that consumers in river food webs shift foraging habits in response to seasonal patterns of connectivity and habitat availability, thus promoting long-term population and community stability.

洪泛区水生生态系统的基础生产来源和影响能量流动的外来来源的投入会经历时间变化。我们分析了碳 (δ ¹³ C) 和氮 (δ ¹⁵N) 来自代表 18 个物种的 449 条鱼肌肉，以表征博茨瓦纳奥卡万戈三角洲下游两条河流中的能量通路。我们在雨季和旱季对鱼类进行取样，并使用混合模型来估计鱼类吸收的主要基础生产来源的比例。我们估计了每个鱼类种群的营养位置 (TP)，并评估了 TP 与单一生产来源支持鱼类生物量的程度之间的关联。在雨季，Boteti 河中的鱼类通过主要来自水生大型植物的食物链吸收物质。在旱季，陆生C ₃植物和陆生C ₄草具有更大的重要性。在博罗河，陆地 C ₃植物被推断为在雨季支持鱼类的重要生产来源，而水生大型植物在旱季变得更加重要。在河流和季节中，对单一来源的依赖程度与 TP 呈负相关，支持了在食物网中处于较高位置的生物倾向于得到多个食物链和基础源的支持，而在食物网中处于较低位置的生物的假设可能得到许多或少数食物链的支持。我们表明，河流食物网中的消费者会根据连通性和栖息地可用性的季节性模式改变觅食习惯，从而促进长期人口和社区稳定。