Intercontinental trends in functional and phylogenetic structure of stream fish assemblages

Area of Science:

• Ecology
• Evolutionary Biology
• Ichthyology

Background:

• Phylogenetic and trait-based approaches have advanced community assembly understanding.
• Limited consensus exists on the relative importance of assembly mechanisms at large scales.

Purpose of the Study:

• To determine the contribution of limiting similarity and environmental filtering to stream fish community assembly.
• To investigate these mechanisms at an intercontinental scale using phylogenetic and trait dispersion.

Main Methods:

• Phylogenetic and trait dispersion analyses were employed.
• Stream fish communities were sampled across five zoogeographic regions.
• Traits related to habitat use and feeding were analyzed.

Main Results:

• Trait underdispersion was more common than overdispersion across spatial scales and species pools.
• Environmental filtering and species interactions were key assembly mechanisms in small streams.
• Stochastic factors also influenced trait dispersion patterns, with some assemblages showing random patterns.
• Lower functional diversity was observed in high-velocity, shallow, and structurally simple microhabitats, supporting the stress-dominance hypothesis.
• Functional and phylogenetic underdispersion suggest niche conservatism and stabilizing selection.

Conclusions:

• Environmental filtering is a deterministic and globally consistent factor shaping stream fish assemblage structure.
• Species interactions and stochastic processes also contribute to community assembly.
• Phylogenetic niche conservatism may play a role in observed underdispersion patterns.