Is the human population a large‐scale indicator of the species richness of ground beetles?

Abstract

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 this 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 the human population density correlates with the species richness of ground beetles in Italy's regions, provinces and 10 Â 10 km (UTM) grid cells. As expected, the observed and estimated (Chao index) number of species increases significantly with increasing human population density for regions, while 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 the total/ widespread species richness and variation in the human population size, while the correlation was negative for endemic species. We found no significant role of habitat heterogeneity in the above relationships. The available distributional data of Carabidae in Italy suggest (1) that the species richness of bio-indicators may not be a reliable measure for regional biological assessment; (2) that some broad-scale human population-biodiversity correlations can be artefactual.

Why is species richness often higher in more densely populated regions?

“…The results of Barbosa et al (2010) at the largest sampling grain contrast with the findings of Luck et al (2010), who examined the congruence between HPD and bird species richness across Australia at a grain size of 11 grid cells. Luck et al (2010) found that the positive correlation between HPD and species richness remained even after controlling for variation in sampling effort.…”

“…After accounting for variation in sampling effort and area, Barbosa et al (2010) find that the positive relationship between Carabid species richness and HPD across regions largely disappears. However, and most surprisingly, they find that the negative correlation between HPD and richness across 10 Â 10 km grid cells reverts to a positive correlation (although the partial r 2 is very small).…”

“…Hugo & van Rensburg, 2008;Steck & Pautasso, 2008;Luck et al, 2010). Barbosa et al (2010) make an important contribution to this research field in three ways. First, they use Carabid beetles as their focal taxonomic group.…”

“…As Barbosa et al (2010) notes, variation in sampling effort has largely been ignored by researchers working on the HPD-species richness correlation, although it could reasonably be described as 'the elephant in the room'. Indeed, the positive correlation between HPD and species richness could simply be an artefact of greater sampling in areas with more people.…”

Positive regional species–people correlations: a sampling artefact or a key issue for sustainable development?

“…In our study (Barbosa et al, 2010), we tested whether a sampling artefact applies to the species-people correlation for carabids in Italy at three spatial grains of analysis. As the commentaries by Luck (2010) and McKinney (2010) point out, there has been little consideration of variation in sampling effort in previous regional studies of the coexistence of biodiversity and people.…”