Coexistence of ecomorphologically similar species in diverse Neotropical ecosystems has been a focus of long-term debate among ecologists and evolutionary biologists. Such coexistence can be promoted by trophic plasticity and seasonal changes in omnivorous feeding. We combined stomach content and stable isotope analyses to determine how seasonal variation in resource availability influences the consumption and assimilation of resources by two syntopic fish species, Psalidodon aff. gymnodontus and P. bifasciatus, in the Lower Iguaçu basin. We also tested the impact of seasonality on trophic niche breadth and diet overlap of these two dominant omnivores. Seasonal changes in resource availability strongly influenced the consumption and assimilation of resources by the two fish species. Both species exhibited high levels of omnivory, characterized by high diversity of allochthonous resources in the wet season. Terrestrial invertebrates were the main component of diet during this season. However, in the dry season, both species reduced their isotopic niches, indicating diet specialization. High diet overlap was observed in both seasons, but the isotopic niche overlap was smaller in the dry season. Substantial reduction in the isotopic niche of P. bifascistus and a shift toward aquatic invertebrates can facilitate coexistence during this season of resource shortage. Feeding plasticity allows omnivorous fish to adjust their trophic niches according to seasonality, promoting the exploitation of different resources during periods of greater resource diversity. This seasonal variation could be an important mechanism that contributes to the resource partitioning and coexistence of dominant omnivores in Neotropical streams.

生态形态相似物种在各种新热带生态系统中的共存一直是生态学家和进化生物学家长期争论的焦点。营养共生和杂食的季节性变化可促进这种共存。我们结合胃含量和稳定同位素分析来确定资源可利用性的季节性变化如何影响两种syn鱼（Psalidodon aff）对资源的消耗和吸收。裸齿and和双侧斜。，位于伊瓜苏河下游盆地。我们还测试了季节性对这两个主要杂食动物的营养生态位宽度和饮食重叠的影响。资源可用性的季节性变化强烈影响着这两种鱼的消耗和同化。两种物种均表现出高水平的杂食性，其特征在于在湿季中异源资源的多样性高。在这个季节，陆生无脊椎动物是饮食的主要组成部分。但是，在干旱季节，这两种物种都减少了其同位素ni，表明其饮食专门化。在两个季节都观察到高饮食重叠，但是在干旱季节，同位素生态位重叠较小。P. bifascistus的同位素生态位显着减少在这个资源短缺的季节，向水生无脊椎动物过渡可以促进共存。喂食可塑性使杂食性鱼类能够根据季节调整其营养位，从而在资源更加丰富的时期促进对不同资源的开发。这种季节变化可能是一个重要的机制，有助于新热带溪流中杂食动物的资源分配和共存。