Island biogeography of urban insects: tenebrionid beetles from Rome tell a different story

Tenebrionid beetle records from 55 sites in urban Rome (Italy) were used to study the influence of structural parameters (area, isolation, forest cover, and shape) of green spaces on species richness and extinction trends. In line with biogeographical predictions, species richness correlated positively with area size of green spaces, extinction was enhanced by isolation and hindered by area size, but, in contrast with common findings, forest extent had a negative impact on tenebrionid persistence. This is explained by the fact that most of tenebrionid species from Rome are associated with open habitats typical of the landscape that characterized the study area before modern urbanization. In contrast with results obtained in other studies of urban ecology, distance to city centre (which expresses the urban-rural gradient) was never recovered as an important correlate of tenebrionid richness or extinction, which may be explained by the fact that tenebrionids include both urban avoider and urban adapter species. These results warn against making generalizations on urban diversity patterns and conservation strategies without reference to past land-use and species characteristics.