Environmental changes caused by hydrological shifts between wet and dry seasons in the tropics drive variation in resource availability and feeding interactions for riverine fish assemblages, but studies of trophic structure typically take place over short time scales that do not adequately capture this variation. In this study, we used analysis of stable isotopes (δ¹³C and δ¹⁵N) to assess seasonal changes in the diversity and relative importance of production sources supporting fish assemblages in La Venta River, the largest tributary of Netzahualcoyotl Reservoir on the Grijalva River in Chiapas, Mexico. Based on established river ecosystem theories, we expected the relative importance of carbon sources supporting fishes to shift seasonally, with greater use of instream resources during low‐water periods and an increasing contribution from terrestrial sources during high‐water periods. Abundant, low‐trophic‐level food resources (i.e., plants and invertebrates) were expected to support most fish species in the wet season, whereas piscivory was predicted to increase as habitat volume declined and fish density increased in the dry season. Somewhat surprisingly, we found that terrestrial energy sources were assimilated more during low‐water conditions at some sites, and ranges of δ¹³C were higher in the dry season. Terrestrial carbon supporting fish production in low‐water periods likely came from riparian plant detritus that remained in the river after flows receded and/or leaf litter that accumulated in the dry season. Ranges of δ¹⁵N were similar across seasons, with no apparent increase in piscivory during the dry season. Higher trophic redundancy was observed in the wet season, likely due to fish taking advantage of the same readily available food items (e.g., pulses of arthropod prey) during high flows. Documenting seasonal use of trophic resources provides critical information as expanding hydroelectric dam construction threatens the natural variability of energy pathways that support fisheries resources in tropical rivers.

中文翻译：

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墨西哥恰帕斯州营养多样性的季节性变化和基础资源支持热带河鱼组合的基础资源的相对重要性

热带地区湿季和干季之间的水文变化引起的环境变化，导致河流鱼类资源的可利用性和摄食相互作用的变化，但是营养结构的研究通常发生在短时间内，不足以捕捉到这种变化。在这项研究中，我们使用稳定同位素分析（δ ¹³ C和δ ¹⁵N）评估拉文塔河的鱼类资源的多样性和相对重要性的季节性变化，拉文塔河是墨西哥恰帕斯州格里雅尔瓦河上最大的Netzahualcoyotl水库支流Netzahualcoyotl水库。根据已建立的河流生态系统理论，我们预计支持鱼类的碳源的相对重要性会随着季节的变化而变化，在低水时期更多地利用河内资源，而在高水时期则更多地使用陆地资源。预计在雨季将有大量低营养水平的食物资源（即植物和无脊椎动物）为大多数鱼类提供支持，而在食水旺季，随着栖息地数量的减少和鱼类密度的增加，食食动物的数量将增加。有点令人惊讶干旱季节¹³ C升高。在低水时期，支持鱼类生产的陆地碳可能来自河岸植物碎屑，这些河屑在水流消退后仍留在河中和/或枯叶积累的枯枝落叶。的δ范围¹⁵ Ñ是跨季节相似，在旱季在piscivory没有明显的增加。在雨季观察到更高的营养冗余度，这可能是由于鱼类在高流量时利用了相同的易于获得的食物（例如节肢动物的猎物）。记录营养资源的季节性使用可提供关键信息，因为扩大的水力发电大坝建设威胁着支持热带河流渔业资源的能源途径的自然可变性。