Data from: Seasonal population and individual niche dynamics in a tetra fish in the Pantanal wetlands

In seasonal tropical regions, rainfall and/or temporary floods during the wet season generally increase the abundance and diversity of food resources to many consumers as compared to the dry season. Therefore, seasonality can affect intraspecific competition and ecological opportunity, which are two important ecological mechanisms underlying population and individual niche variations. Here, we took advantage of the strong seasonality in the Pantanal wetlands to investigate how within- and between-individual diet variations relate to seasonal population niche dynamics of the tetra fish Astyanax lacustris. We quantified dietary niche using gut contents and stable isotopes. Tetras had higher gut fullness and better body condition in the wet season, suggesting that competition is more intense in the dry season. The population niche was broader in the wet season due to an increase in diet divergence between individuals, in spite of potential stronger competition in the dry season. We posit that low ecological opportunity in the dry season limits the diversifying effect of intraspecific competition, constraining population niche expansion. Our results add new insights on how seasonality affects population and individual diets, indicating that intraspecific competition and ecological opportunity interact to determine temporal niche variations in seasonal environments.

在季节性热带区域，相较于旱季，湿季的降雨及/或临时洪水通常可提升多数消费者可利用的食物资源丰度与多样性。因此，季节节律会影响种内竞争与生态机会——这两大核心生态机制是种群及个体生态位变异的重要基础。本研究依托潘塔纳尔湿地强烈的季节波动特征，以湖形丽脂鲤（*Astyanax lacustris*）为研究对象，探究个体内与个体间的食性变异如何与该物种种群生态位的季节动态相关联。我们通过胃含物分析与稳定同位素技术量化食性生态位。结果显示，湿季中该脂鲤的胃饱满度更高、体况更佳，表明旱季的种内竞争更为激烈。尽管旱季存在更强的潜在竞争压力，但种群生态位在湿季却更为宽泛，这源于个体间食性分化程度的提升。我们提出，旱季较低的生态机会会限制种内竞争的生态位分化效应，进而制约种群生态位的扩张。本研究结果为理解季节变化如何调控种群与个体食性提供了新视角，证实种内竞争与生态机会的交互作用决定了季节性环境中的时间生态位变异。