Modeling Stream Fish Assemblages with Niche Apportionment Models: Patterns, Processes, and Scale Dependence

Abstract

Abstract.-Understanding patterns in terms of the mechanistic processes that produce them is the essence of ecology. However, many studies merely document nonrandom patterns of species coexistence without providing insight into the structuring mechanisms and their scale dependence. Moreover, few studies address the mechanisms driving functional diversity. The objectives of this study were to document empirical patterns of species coexistence within stream fish assemblages across a broad geographic region, addressing both the functional and taxonomic organization of those assemblages, and to determine whether the structuring mechanisms are scale dependent. We gathered data from a report published by the Texas Parks and Wildlife Department that provided empirical species abundance distributions for 62 assemblages from 7 ecoregions and 18 river basins. For each assemblage, we simulated expected species abundances using five previously published models of niche apportionment. These models generate relative abundances in proportion to niche breadth and are constrained to maintain observed species richness, but they do not include information on species identity. These models included four stochastic variants of a geometric series (dominance preemption, random fraction, broken stick, and dominance decay) in which species abundances relate directly to niche breadth and one model (random assortment) in which abundances are independent of niche partitioning altogether. To assess scale dependence, we repeated the analyses after pooling assemblages by ecoregion, river basin, and the entire state. The patterns of niche apportionment for assemblages pooled according to river basin are more consistent with local assemblages than with assemblages pooled according to ecoregions or the entire state. These results suggest that niche apportionment plays a crucial role in structuring stream fish assemblages and that functional groups divide niche space more evenly than do species.

Food-resource partitioning among fish species from a first-order stream in northwestern Paraná, Brazil

“…However, some mechanisms are still little understood by ecologists, such as resource partitioning and other factors that allow the species to coexist (Esteves & Galetti, 1994;Gerking, 1994;Higgins & Strauss, 2008). Therefore, dietary analysis may reveal important information about trophic dynamics and resource partitioning among fish species (Ross, 1986), especially with regard to environments that are subject to sudden changes, such as streams (Johnson & Arunachalam, 2012).…”

Effects of land use on fish assemblages in Patagonian low order streams

“…The understanding of the relationships among landscape, stream characteristics and fish assemblages has thus motivated several studies (e.g. Poff, 1997;Porter et al, 2000;Higgins and Strauss, 2008). Some of these studies indicated that fish assemblages can be structured not only by local processes, but also by large-scale environmental factors (Magalha˜es et al, 2002;Hoeinghaus et al, 2006).…”

Fish-based groups for ecological assessment in rivers: the importance of environmental drivers on taxonomic and functional traits of fish assemblages

“…Indeed, the analysis of functional organization of fish assemblages allows characterizing different aspects of the community structure other than taxonomic organization (Hoeinghaus et al, 2007;Higgins and Strauss, 2008) and permit comparisons among broad geographic regions even when communities present different taxa (Simberloff and Dayan, 1991). In the Iberian Peninsula this approach will contribute to avoid problems related to spatially restricted endemisms.…”