Fish assemblage convergence along stream environmental gradients: an intercontinental analysis

Abstract

Species that pass through similar environmental filters, regardless of geographic proximity or evolutionary history, are expected to share many traits, resulting in similar assemblage trait distributions. Convergence of assemblage trait distributions among different biotic regions would indicate that consistent ecological processes produce repeated patterns of adaptive evolution. This study analyzes trait–environment relationships across multiple stream fish assemblages representing evolutionarily divergent faunas. We hypothesized that trait–environment patterns converge across regional faunas in response to a common set of environmental filters acting on functional traits. One hundred and ninety‐seven species and forty streams were sampled from five regions: Belize, Benin, Brazil, Cambodia and USA. By examining trait–environment plots, multiple congruent trait–environment patterns were found across all regions, indicative of a consistent set of environmental filters acting on local community assembly. The consistency of these patterns strongly suggests that water velocity and habitat structural complexity function as universal environmental filters, producing similar assemblage trait distributions in streams across all regions. Bivariate relationships were not universal, and only one of the associations between a single functional trait and single environmental variable was statistically significant across all five regions. Strong phylogenetic signal was found in traits and habitat use, which implies that niche conservatism also influenced assemblage trait distributions. Overall, results support the idea that habitat templates structure trait distributions of stream fish assemblages and do so in a consistent manner.

Intercontinental trends in functional and phylogenetic structure of stream fish assemblages

“…In stream fishes, functional diversity metrics were related to water depth, substrate complexity, and water velocity in a manner consistent with the stress‐dominance hypothesis. This pattern was fairly congruent across regions (Table ; Bower & Winemiller, ). FRic was inversely associated with water velocity, suggesting that requirements for coping with hydraulic drag restrict assemblage trait space in stream microhabitats with fast flows.…”

“…In stream fishes, functional diversity metrics were related to water depth, substrate complexity, and water velocity in a manner consistent with the stress-dominance hypothesis. This pattern was fairly congruent across regions (Table S5; Bower & Winemiller, 2019).…”

“…Within each region, stream reaches measuring from 200 to 500 m were sampled in an upstream direction to obtain representative samples of fishes from major types of microhabitat (see Bower & Winemiller, ). Microhabitat types were areas of relatively homogeneous depth, current velocity, substrate composition, and in‐channel cover.…”

“…Structurally complex substrates can provide refuge from adverse environmental conditions, such as hydraulic drag or predation (Bartholomew, Diaz, & Cicchetti, 2000;Tokeshi & Arakaki, 2012). Streams with unstructured substrates tend to have fish assemblages with lower functional trait diversity (Bower & Winemiller, 2019;Kovalenko et al, 2012).…”

Landscape factors modulating patterns of salmonid distribution during summer in north Patagonian rivers

“…Local scale variables, like water velocity and habitat structural complexity, have been reported to function as universal environmental filters, producing similar assemblage trait distributions in streams across different regions (Bower & Winemiller, 2019). Studies conducted on a wider spatial scale found instead a greater effect of landscape variables over local ones (Esselman & Allan, 2010).…”