Richness and abundance of stream fish communities in a fragmented neotropical landscape

Abstract

Environmental conditions influence ecological processes that shape stream community diversity and abundance. Deforestation has the potential to limit available particulate organic matter and raise stream temperatures. The degree to which tropical stream communities are impacted by these changes is likely to differ between systems, but empirical data from tropical regions are lacking. This lack of baseline data hinders conservation policy as well as efforts to better understand biogeographic and anthropogenic impacts on species’ distributions. To fill this knowledge gap, we surveyed 27 sites in six previously unstudied streams across a gradient of deforestation in northwest Ecuador and assessed the degree to which localized deforestation predicted patterns of community composition of fishes. Using general linear mixed models and AICC we found that neither forest fragmentation nor canopy closure was a significant predictor of species richness and found no difference between the species richness of fragmented and continuous sites. However, forest fragmentation was a strong predictor of abundance, occurring in 31 of 31 general linear mixed models, with higher abundance in fragmented forest than in continuous forest. Of 16 species found, eight occurred at five or more sites and one (Pseudochalceus boehlkei), numbered 200 out of 627 individuals. NMDS and SIMPER analysis suggested that community composition differed between fragmented and continuous sites. P. boehlkei, Pseudopoecilia fria, and Astroblepus cf. fissidens species presented in higher abundances in deforested sites, possibly suggesting a less functionally diverse community. This pattern is consistent with neotropical streams that have experienced partial deforestation but not total degradation of habitat.