Dry Season Feeding Profiles of a Characiformes Assemblage in a Brazilian Tropical Stream.

Abstract

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 <i>Astyanax</i> cf. <i>bimaculatus</i> and <i>Characidium</i> cf. <i>bimaculatum</i> exhibiting the broadest niches. Specialization occurred in <i>Curimatopsis</i> cf. <i>cryptica</i> (85.07% plant material), and there was significant dietary segregation, with indicator species analysis linking <i>Astyanax</i> cf. <i>bimaculatus</i> to piscivory and <i>Knodus guajajara</i> to vermivory. Pianka's index revealed a wide gradient of trophic niche overlap, with the highest overlap observed between <i>Hyphessobrycon piorskii</i> and <i>Knodus guajajara</i> (0.95), and between <i>Holopristis</i> cf. <i>ocellifera</i> and <i>Nannostomus beckfordi</i> (0.96). Morphological PCA associated traits with feeding strategies, including caudal fin length (<i>Astyanax</i> cf. <i>bimaculatus</i>), body depth (<i>Curimatopsis</i> cf. <i>cryptica</i>), and oral gape width (<i>Bario oligolepis</i>). 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. The results demonstrate how dry-season resource scarcity promotes trophic divergence via morphological specialization, with generalists (<i>Astyanax</i> cf. <i>bimaculatus</i>) coexisting with specialists through niche partitioning, which is critical for conservation in this threatened urban-protected area.