Trophic plasticity of omnivorous fishes in natural and human‐dominated landscapes

Abstract

The persistence of diverse communities and functioning ecosystems under increasing anthropogenic pressure relies on food web rewiring and the ability of animals to expand or change their diet in disturbed ecosystems. We combined a suite of diet tracing techniques to study trophic plasticity in omnivorous fishes, ecomorphologically similar species with high competition potential, across different human land uses in subtropical streams. We found that the proportion of native forest cover, associated with intensive land use, altered the isotopic composition of fishes, which were more enriched in 13C, without affecting the carbon isotope ratios of their prey and basal resources. There was also evidence for a nonlinear effect of native forest cover on the δ15N values of basal resources, macroinvertebrates, and omnivorous fishes, indicating that nutrient pollution from agriculture propagated through stream food webs. The most widely distributed fish species shifted their diet from autochthonous resources to terrestrial invertebrates and sedimentary organic matter in disturbed streams. Moreover, the isotopic niche of this fish species was broader in streams with higher fish species richness, indicating the combined impacts of environmental change and competition on species coexistence. Therefore, our findings showed that the dominance and trophic niche breadth of dominant omnivores depend not only on the availability of resources but also on the interactions with their putative competitors.

Untangling the complex food webs of tropical rainforest streams

“…These two mechanisms critically depend on the maintenance of local and regional biodiversity in tropical streams, which is known to be strongly affected by human land use intensifications from forests to monoculture plantations in different ways (Neves et al, 2023;Siqueira et al, 2015). Therefore, an urgent challenge is to understand how the systematic loss of diversity jeopardizes the stability of stream food webs under human impacts and what could be the consequences for a sustainable use of resources.…”

Linking anatomical and histological traits of the digestive tract to resource consumption and assimilation of omnivorous tetra fishes

“…Although the trophic ecology of these species has been extensively studied (Bonato et al, 2018;Delariva & Neves, 2020;Neves et al, 2023;Pini et al, 2019), we still know little about the histological characteristics of their digestive tract and how these traits are related to food ingestion, digestion, absorption, and assimilation. Moreover, recent stable isotope analyses indicate that while tetra fishes readily ingest plant food items, they rarely assimilate or incorporate these types of food into their tissues (Bonato et al, 2018;Neves et al, 2021Neves et al, , 2023. This finding raises questions about the role of plant material in the diets of tetra fishes.…”

“…In this study, we explored the relationships among morphological characteristics of the digestive tract, food intake, isotopic composition, and resource assimilation of three native omnivorous fish spe- (Neves et al, 2023). Consequently, our study aimed to accomplish the following objectives: (i) describe the anatomical, histological, and histochemical traits of the digestive tract and diet of these small tetra fishes; (ii) investigate the potential relationship between intestine length, diet, and isotopic composition given their omnivorous feeding habit; and (iii) test the hypothesis that variations in the digestive tract among the species correspond to differences in resource utilization (animal and plant food items), isotopic composition, and assimilation.…”

“…Psalidodon, Astyanax, and Bryconamericus are the most species-rich genera of the Characidae family. Omnivorous diet and trophic plasticity have been well documented for these genera that often consume both animal and plant food items (Bonato et al, 2018;Neves et al, 2023;Pini et al, 2019). These species are often opportunistic feeders with the ability to change their diet across seasons and space depending on food resource availability (Neves et al, 2021(Neves et al, , 2023Pini et al, 2019;Quirino et al, 2015).…”

“…These species are often opportunistic feeders with the ability to change their diet across seasons and space depending on food resource availability (Neves et al, 2021(Neves et al, , 2023Pini et al, 2019;Quirino et al, 2015). Although the trophic ecology of these species has been extensively studied (Bonato et al, 2018;Delariva & Neves, 2020;Neves et al, 2023;Pini et al, 2019), we still know little about the histological characteristics of their digestive tract and how these traits are related to food ingestion, digestion, absorption, and assimilation. Moreover, recent stable isotope analyses indicate that while tetra fishes readily ingest plant food items, they rarely assimilate or incorporate these types of food into their tissues (Bonato et al, 2018;Neves et al, 2021Neves et al, , 2023.…”