Headwater Stream’s Fish Assemblages: What Diversity and Environment Tell us about their Structure and Organization?

Understanding the relationship among descriptors of community diversity and the response of these descriptors to the environment is a cornerstone to ecological studies. In this study, we used a set of headwater stream’s fish assemblages to answer two questions: 1) How do distinct descriptors of fish assemblage’s diversity are related to each other at headwater streams?; 2) How does environment influences each descriptor of fish assemblage’s diversity at headwater streams? As metrics of community structure/diversity, we used the number of species (species richness, S) and individuals (abundance, N), taxonomic distinctiveness (taxonomic diversity, Δ+), and the mean pairwise distance (functional diversity, MPD). The environmental variables evaluated were the following: channel depth and channel width, altitude, riparian vegetation cover, water turbidity and water temperature, dissolved oxygen, pH, and conductivity. The relationship among descriptors of fish assemblage’s diversity and between these descriptors with the environment was tested with a Spearman’s correlation analysis. We found a positive correlation between: i) Δ+ and MPD; and ii) N and Δ+ with channel width and temperature, respectively. These findings provide evidence that different descriptors of fish assemblage’s diversity are influenced by different variables of the environment at headwater streams. Moreover, we observed the existence of a spatial congruence between Δ+ e MPD, suggesting that the development of strategies for protecting one of these descriptors may also help to preserve the other one. Our study provides important information for a region of the Central Brazil, the Upper Paraná River basin, that remains not well known regarding to its fish fauna when compared to other localities in this same region or within its hydrological domain.