Trophic interactions between fish and their resources depends on resource availability and interspecific competition. To understand dry season trophic profiles of a speciose Characiformes assemblage we performed stomach content analysis to describe diet and determine levels of niche partitioning and morphological adaptations among eight Characiformes species in the dry season in Mata de Itamacaoca, Chapadinha Municipality, State of Maranhão, northeastern Brazil. Insectivory dominated most diets, with Astyanax cf. bimaculatus and Characidium cf. bimaculatum exhibiting the broadest niches. Specialization occurred in Curimatopsis cf. cryptica (85.07% plant material) and there was significant dietary segregation with indicator species analysis linking Astyanax cf. bimaculatus to piscivory and Knodus guajajara to vermivory. Pianka index showed extreme niche overlap variations, with the highest overlap between Bario oligolepis and Characidium cf. bimaculatum (1.68), and between Astyanax cf. bimaculatus and Nannostomus beckfordi (1.64). Morphological PCA associated traits with feeding strategies: caudal fin length (Astyanax cf. bimaculatus), body depth (Curimatopsis cf. cryptica), and oral gape width (Bario oligolepis). Mixed models confirmed insects and plant material with a marginally significant effect as key drivers of dietary variation. Therefore, the assemblage shows high niche overlap combined with diverse trophic profiles. Results presented here demonstrate how dry season resource scarcity promotes trophic divergence via morphological specialization, with generalists (Astyanax cf. bimaculatus) coexisting with specialists through niche partitioning, which is critical for conservation in this threatened urban-protected area.
Morphological adaptations, Neotropical fishes, Resource partitioning, Seasonality, Trophic ecology
