Taxonomic and functional organization in metacommunity structure of stream-fish assemblages among and within river basins in Texas

Abstract

Metacommunities are spatially structured communities linked by dispersal. They provide a connection between local community assembly and regional-level processes. One of the more widely used methods to address questions related to metacommunity concepts is those that characterize elements of metacommunity structure by quantifying aspects of coherence, species turnover, and boundary clumping. In this study, we used this approach to study the spatial ecology of freshwater fishes in Texas. Stream-fish assemblages in Texas provide an excellent opportunity to examine the patterns of metacommunity structure due to the number of drainages that empty directly into the Gulf of Mexico, which minimizes the likelihood of dispersal between basins while allowing for longitudinal movement within basins. We used fisheries data published by the Texas Parks and Wildlife Department and from the North American Water Quality Association, which consisted of 94 sampling localities distributed across 18 river basins and 11 ecoregions. To examine within-basin patterns, we focused only on the Brazos, Colorado, and Trinity rivers because of the number of sites within each of these basins. From a taxonomic standpoint, we consistently observed Clementsian patterns regardless of whether it was among or within river basins, whereas we mostly observed Gleasonian patterns from a functional perspective. Only one functional group was found at all sites in each of the three main river basins, which consisted of invertivores with an equilibrium life-history strategy. Various bioclimatic variables were significantly correlated with metacommunity structure, but these correlations differed between taxonomic and functional organization and differed depending on which river basin was considered. The results of this study support previous findings that species composition and functional traits relate to environmental gradients, but further our understanding by providing additional evidence that species sorting processes are the dominant structuring mechanisms.