Examination of contemporary (ecological) and historical (evolutionary) relationships within fish assemblages may provide understanding of the relative influences of competitive exclusion and habitat filtering assembly mechanisms. However, interpretation of relationship patterns (e.g., even or clustered) must consider niche conservatism, ecological convergence, abundance weighting, and spatial scale for proper understanding. The goals of this study were to identify influences of habitat filtering and competitive exclusion assembly mechanisms in darter (Percidae: Etheostomatinae) assemblages in the Duck River, Tennessee, and to build a conceptual framework describing the intricacies of assembly within this species-rich system. Phylogenetic relatedness, abundance weighting, habitat use similarity, functional morphological relatedness, and niche conservatism (for habitat use and morphology) were quantified for 15 darter assemblages along the stream gradient to elucidate magnitude and progression of assembly mechanisms. Habitat filtering was identified as a primary contributor to assembly based on findings of phylogenetic clustering and consistent co-occurrence of species that shared similar habitat requirements. Morever, lack of habitat use conservatism suggested that darters of two clades (both well represented in assemblages of the study) have converged on similar habitat needs in the system. Competitive interactions may have followed the initial habitat filter, as demonstrated by limiting morphological similarity within assemblages. This study demonstrates the importance of accounting for contemporary and historical factors to identify magnitude and progression of assembly mechanisms in fish assemblages. Furthermore, this study builds upon previous darter assembly work and provides a novel illustration of how habitat use convergence between phylogenetic clades can alter interpretations of assembly mechanisms in species-rich communities.
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Vol. 107 • No. 3