Mayara Pereira Neves , Raul Costa‐Pereira, Rosilene Luciana Delariva, Clarice Bernhardt Fialho

The drivers of intraspecific niche variation and its effects on species interactions are
still unclear, especially in species-rich Neotropical environments. Here, we investigated
how ecological opportunity and interspecific competition affect the degree
of individual trophic specialization and the population niche breadth in tetra fish.
We studied the four ecologically similar species (Psalidodon aff. gymnodontus, P. aff.
paranae, P. bifasciatus, and Bryconamericus ikaa) in subtropical headwater streams
(three sites with two co-occurring species and three sites with only one species). We
sampled fish in two contrasting seasons (winter/dry and summer/wet) and quantified
their trophic niches using gut content analysis. Psalidodon bifasciatus was the
only species distributed over all the sampled streams. We observed seasonal differences
in population trophic niche breadth of P. bifasciatus just when this species
co-occurred with P. aff. gymnodontus. These findings confirm the complex nature of
the effects of interspecific competition, depending, for instance, on the identity of
the competitor. The degree of individual specialization of P. bifasciatus was higher in
the winter, and it was not influenced by the presence of another species. Conversely,
the other two Psalidodon species studied presented greater individual specialization
in the summer, when fish consumed a higher proportion of allochthonous items (terrestrial
insects and seeds), and there were no effects only for B. ikaa. Herein, our
results suggest that seasonality in food-resource availability is a major driver of niche
variation and it has the potential to play an important role in how these similar tetra
species interact and coexist.

link: https://onlinelibrary.wiley.com/doi/epdf/10.1111/btp.12879

F I G U R E 1 Species studied: (a) Psalidodon aff. gymnodontus (UFRGS 25,725, 95.4 mm SL); (b) Psalidodon aff.
paranae (UFRGS 26,232, 48.0 mm LS); (c) Psalidodon bifasciatus (UFRGS 26,235, 85.0 mm SL); and (d) Bryconamericus ikaa (UFRGS 26,246, 49.0 mm SL)

F I G U R E 2 (a) Boxplot of population trophic niche breadth (estimated as distance to centroid, PERMDISP) of P. bifasciatus (Pbi) in streams with co-occurring characid species (S1, S2, and S3) and in allopatry (S4, S5, and S6). B) Population trophic niche breadth of three characid fish species (Pag = P. aff. gymnodontus; Pap = P. aff. paranae) in co-occurrence with P. bifasciatus collected during the winter and summer seasons. Box lower and upper endpoints represent the 25th and 75th quartiles, respectively. The horizontal bar inside each box represents median diet breadth