Locations of surveys whose data were used in the analysis, by major taxonomic group of study.

Shown in the Lambert cylindrical equal area projection. Point diameters are proportional to the (loge) number of sites sampled by each survey, and are translucent so areas of opaque colour indicate overlapping points. Studies are coloured according to the taxa sampled within the study. The outline map is based on the World Bank map of river basins (https://bit.ly/2J86Kbq), which is published under a CC-BY 4.0 license. The site-level data underlying this figure are freely available (DOI: 10.6084/m9.figshare.7262732).