Seasonal feeding plasticity can facilitate coexistence of dominant omnivores in Neotropical streams

Abstract

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.

Niche overlap in rodents increases with competition but not ecological opportunity: A role of inter‐individual difference

“…While niche partitioning between coexisting species at a single site is well documented, relatively fewer studies examined these patterns across multiple natural communities. Furthermore, although ecological theory predicts that competition, in particular intraspecific competition, plays a key role mediating niche partitioning (Chase & Leibold, 2009; Chesson, 2000; MacArthur, 1970), the role of competition is more often implied using proxies such as season, consumer abundance and resource abundance (Costa‐Pereira et al, 2018, 2019; de Camargo et al, 2021; Neves et al, 2021; Sánchez‐Hernández et al, 2021) without evidence for negative impacts of competition on individuals and/or populations.…”

Allochthonous resources are less important for faunal communities on highly productive, small tropical islands

“…( 2016 ) and Neves et al. ( 2021 ). Vertical and horizontal error bars indicate mean ± standard deviations of the four investigated basal resources…”

“…The isotope signatures (δ 13 C and δ 15 N) are plotted for each primary consumer, that is, herbivores and detritivores, together with the mean isotope signature of the four basal resources from the four investigated islands (N = 5). Isospace plots have been corrected assuming 1 trophic enrichment factors (TEFs) for primary consumers, following the method described in Neres-Lima et al ( 2016) and Neves et al (2021). Vertical and horizontal error bars indicate mean ± standard deviations of the four investigated basal resources models showed a great variability in the relative contribution of allochthonous resources (i.e., seagrass and marine carrion combined) among invertebrate consumer species but an overall consistency within species sampled in the beach and inland habitat, that is, either a high or a low proportion in both habitats (Table 3, Table S2).…”

“…The isotope signatures (δ 13 C and δ 15 N) are plotted for each secondary consumer, that is, omnivores and carnivores, together with the mean isotope signature of the four basal resources from the four investigated islands (N = 5). Isospace plots have been corrected assuming 2 trophic enrichment factors (TEFs) for secondary consumers, following the method described in Neres-Lima et al (2016) and Neves et al (2021). Vertical and horizontal error bars indicate mean ± standard deviations of the four investigated basal resources inland and beach habitat than Arachnida, Formicidae, and Gryllidae from both habitats (Tukey HSD: p < .05 for all pairwise comparisons).…”

“…herbivorous and detritivorous consumers, we used trophic enrichment factors (TEFs) for terrestrial consumers without acidification treatment of +0.5 ± 0.17‰ for 13 C and +2.4 ± 0.24‰ for 15N (McCutchan et al, 2005). For omnivorous and carnivorous consumers, we doubled the TEF and calculated the variability using (2 × SD 2 ) 0.5 following the method described inNeres-Lima et al (2016) andNeves et al (2021).…”