Barbosa A.M., Fontaneto D., Marini L. & Pautasso M.

Empirical evidence has often shown a large-scale positive co-occurrence of biodiversity-rich and densely populated regions. This biogeographical pattern has important implications for conservation biology. Previous studies have supported two of the potential mechanisms behind such pattern: the distributions of biodiversity and of human beings tend to match climatic patterns, and human beings have settled in regions of higher habitat heterogeneity or they may have increased it. There has been little testing and evidence for an artefactual explanation: more populated regions may show more species only because of a more thorough sampling. Using a new country-wide dataset, we tested whether human population density correlates with species richness of ground beetles in Italy’s regions, provinces and 10*10km (UTM) grid cells. As expected, the observed and estimated (Chao index) number of species increases significantly with increasing human population density for regions, whilst there is no significant variation for provinces. But this is not the case when controlling for sampling effort. Variations in observed and estimated species richness are primarily associated with the available number of records, which is in turn well correlated with human population size. These results were confirmed for endemic and widespread species richness. At the UTM level, when controlling for sampling effort and area, there was a significant positive correlation between total/ widespread species richness and variation in human population size, whilst the correlation was negative for endemic species. We found no significant role of habitat heterogeneity in the above relationships. The available distributional data of ground beetles in Italy suggests (1) that species richness of bioindicators may not be a reliable measure for regional biological assessment, and (2) that some broad-scale human population-biodiversity correlations can be artefactual.