Data from: Can ancestry and morphology be used as surrogates for species niche relationships?

Species interactions are difficult to quantify, and, consequently, many
studies have used species traits and phylogeny as proxies under an
assumption of niche conservatism (i.e., closely related and
morphologically similar species should have similar niches). However, few
studies have investigated whether niches actually are conserved within and
across diverse communities. Here, we tested the degree to which
phylogenetic relatedness and morphological similarity predict diets and
stable isotopic ratios (δ15N and δ13C), two common descriptors of the
trophic niche, in fish assemblages of two small streams in the Neotropics.
We also tested the strength of the association between isotopic ratios and
diet composition and found significant correlations implying that isotopic
signals reveal trophic structure despite error associated with estimates
of trophic enrichment and variation associated with tissue preservation,
metabolism, and other factors affecting isotopic ratios. Morphological
traits yielded a significant phylogenetic signal, and both morphological
traits and phylogeny were correlated with diet composition, with
morphological traits being a stronger predictor. We infer that
functionally relevant morphological traits of fish can be used to infer
trophic niches for certain kinds of questions and analyses when trophic
data are lacking. However, we highlight that using phylogenetic and
morphological data in combination with dietary and/or isotopic data can
improve resolution of assemblage trophic structure and niche
diversification.