Global congruence of riverine fish species richness and human presence

Abstract

Aim: Discharge is a key determinant of biodiversity in rivers. Positive relationships between riverine biodiversity and discharge, also called species–discharge relationships (SDRs), have been widely documented. However, potential human influences on these relationships are typically not considered. We aimed to fill this gap by exploring whether and how the slopes and intercepts of global riverine fish SDRs might be affected by human pressure on the environment. Location: Global. Time period: Current. Major taxa studied: Riverine fishes. Methods: We first quantified native riverine fish species richness of 4,430 catchments of >500 km2 in size with available discharge measurements, using a novel dataset of the global distributions of 11,425 riverine fish species. We then established mixed effects models relating fish species richness to discharge and to two aggregated human pressure variables: the human footprint index (HFI) and the fragmentation status index (FSI). We tested for possible interactions between discharge and the human pressure variables, while accounting for other relevant covariates of large-scale gradients in riverine fish diversity. Results: Against our expectations, we found positive coefficients for both HFI and FSI, in addition to a positive interaction between FSI and discharge. We found this consistently for different discharge variables (annual mean, maximum weekly and minimum weekly discharge). These findings suggest that riverine fish species richness tends to be higher in catchments characterized by more anthropogenic alterations of the natural environment. Main conclusions: The global congruence between riverine fish species richness and human presence might reflect a commonality of drivers as well as biodiversity data gaps in the most pristine and species-rich catchments. Irrespectively, our results indicate that conflicts between human development and conservation are not easily avoided and highlight the challenges involved in safeguarding global freshwater biodiversity.