Environmental degradation of streams leads to the loss of ecomorphologically similar fish species

Human activities change the environmental conditions of streams and alter their assemblages. However, the environmental factors associated with the change in the ecomorphological similarity of the fish assemblage have not been investigated enough. In this context, we sampled data from three urban and six rural streams in the Pirapó River Basin to assess which environmental factors influence the taxonomic and ecomorphological structures of the fish assemblage. We hypothesized that (1) streams with greater environmental heterogeneity have higher species diversity; (2) the greater species diversity is associated with a greater diversity of body shapes and coexistence of more ecomorphologically distinct species. Twenty-two ecomorphological indices related to the food acquisition, locomotion, and habitat use of species were used to calculate interspecific ecomorphological distances that were analyzed using principal component analysis and multiple linear regression. The results show that the rural streams showed less degraded environmental conditions and greater environmental heterogeneity than the urban ones, which was related to the increase in species diversity and ecomorphological similarity of the assemblage. We can conclude that streams containing greater environmental heterogeneity can support more diverse fish assemblages. Furthermore, environmental degradation results in the loss of ecomorphologically similar species, in which only those with distinct ecological requirements remain in the degraded streams. Therefore, conservation efforts that aim at sustaining environmental heterogeneity and mitigating urban land use do not only maintain the species’ diversity, but also the coexistence of ecomorphological similar fishes.