Effects of urbanization and environmental heterogeneity on fish assemblages in small streams

Abstract

The structure of freshwater assemblages may be driven directly by urbanization or indirectly by a reduction in environmental heterogeneity (EH). Disentangling the effects of urbanization and EH requires uncorrelated proxies of each of these factors. We assessed the effects of the degree of urbanization and EH on the structure of fish assemblages. We sampled fish in 45 streams located in the urban area of Cuiabá. We assessed the effects of urbanization and EH on rarefied fish species richness (Srarefied), the local contribution to beta diversity (LCBD), and composition with linear models and distance-based redundancy analysis. Our indexes of urbanization and EH were not correlated. We found that both Srarefied and the LCBD decreased with an increasing degree of urbanization, but were not associated with EH. We also noted that few native fish species abundances were associated with the EH. Serrapinnus microdon, S. calliurus, Hemigrammus tridens, and Astyanax lacustris were abundant in streams with a lower degree of urbanization. The non-native Poecilia reticulata was more abundant in streams with a higher degree of urbanization. Our results highlight that urbanization leads in negative impacts on fish assemblages, such as decreases in diversity and the dominance of non-native species.

Effects of environment and metacommunity delineation on multiple dimensions of stream fish beta diversity

“…While land use variables provide the first evidence that urbanization and agriculture change fish communities, pinpointing the specific variables associated with these land uses can give additional insight into what environmental monitors should be measured when completing bioassessments (Waite et al, 2021;Iacarella, 2022). For example, Stoczynski et al (2021) found that dam density affected how species replaced one another across the landscape, Ortega et al (2021) identified impervious surfaces as a proxy for urbanization, and Waite et al (2021) highlighted how contaminants in water and sediment were just one of multiple urbanization and agricultural stressors. Thus, disentangling anthropogenic effects from 'natural' environmental variables in metacommunity analyses may increase our ability to explain factors structuring beta diversity within metacommunities (Duarte et al, 2018;Gianuca et al, 2018).…”