A test of the species-people correlation for stream macro-invertebrates in European countries

Many recent studies have shown that over large scales there are positive correlations between plant and vertebrate species richness and human population presence. It is unknown whether this pattern applies also to Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) (EPT), which are common bio-indicators of the naturalness of streams. Most local studies report higher species richness of these macro-invertebrates where human influences on water quality are lower. Using a newly collated taxonomic data set, we studied whether the species richness of EPT is related to human population size in European countries. Analyses controlled for country area, plant species richness, and mean annual temperature and precipitation. We found a significant increase in the number of EPT species with increasing human population size, plant species richness, and decreasing temperature. Our analysis confirmed the scale dependence of the human population-biodiversity correlation. Although stream macro-invertebrates are traditionally used as indicators of pristine ecosystems over local to regional scales, over broad scales more populated regions have more EPT species than less populated ones. This finding underlines the importance of scale in ecology and implies that there is a challenge also for the broadscale conservation of EPT diversity.