Use of taxonomic and chorological diversity to highlight the conservation value of insect communities in a Mediterranean coastal area: the carabid beetles (Coleoptera, Carabidae) of Castelporziano (Central Italy)

We used the carabid beetles inhabiting the Castelporziano Presidential Estate reserve (a natural reserve of some 60 ha facing the Tyrrhenian sea) to show how chorotypes (i.e. species distribution types) can be used to characterise insect communities. We compared three forms of diversity: species richness, Clarke and Warwick taxonomic diversity and chorological composition. Chorological composition was modelled using Menhinick, Margalef, Shannon, and Brillouin diversity, Simpson dominance, Pielou evenness and Buzas and Gibson evenness. Variations in carabid species richness, chorological composition (richness, diversity, dominance and evenness) and taxonomic diversity among biotopes followed different patterns thus providing complementary not redundant information. Beach, dunes, high maquis and oak forest were biotopes with low species richness, whereas wet woodlands, mixed forest, wet zones and open areas have high species richness. Low maquis had an intermediate position. This subdivision is substantially confirmed by indices of chorological composition. However, in contrast with large variations in diversity indices, evenness was substantially similar, and relatively high in all biotopes, even those with very small numbers of species. Taxonomic diversity was also similar among biotopes, being however small in oak forests and open areas. When species richness, chorological diversity and taxonomic diversity were used to calculate an index of overall conservation interest, the most important biotopes resulted to be wet zones, wet woodlands, open areas and mixed forest. These results clearly indicate that the carabid communities with high conservation values are those associated with humid environments. This is consistent with the hypothesis that most of the carabids species occurring in the study area are hygrophilous elements, associated with wetlands, which shifted their range southwards during the glacials, and which form a relict component of the carabid fauna of coastal areas.