When human needs meet beetle preferences: tenebrionid beetle richness covaries with human population on the Mediterranean islands

1. Human presence can affect biodiversity in many ways. If anthropization is one of the major drivers of species extinctions, at the same time, human induced increase in environmental heterogeneity may also increase species richness. 2. In many cases, however, heterogeneity is not enough to explain the unexpectedly high biodiversity found in some densely populated areas. 3. A possible explanation to such situations is the partial overlap in resource requirements between man and other species, which promotes a tendency for humans to settle in sites characterised by environmental conditions that are particularly favourable also for many other organisms. 4. To test this hypothesis, we investigated the relationships between human population and species richness of native (non-synanthropic) tenebrionid beetles in the Mediterranean islands, many of which have been inhabited by humans for millennia. 5. Using partial correlation analyses, we found that tenebrionid diversity increased not only with island area and maximum elevation (used herein as a measure of environmental heterogeneity), but also with human population. 6. This may suggest that the islands that were (and are) more accessible and hospitable to humans are also those which can be more easily colonised by tenebrionids, owing to their larger areas and higher environmental heterogeneity.