Cumulative annual dung beetle diversity in Mediterranean seasonal environments

Species diversity assessments should consider the dynamic nature of ecological communities, especially in highly seasonal ecosystems. Here we provide a comprehensive framework for analysing seasonal changes in species composition, richness and diversity in two local dung beetle (Coleoptera: Scarabaeoidea: Aphodiidae, Geotrupidae, and Scarabaeidae) communities from Western Tuscany (Italy), in the Mediterranean ecoregion. We test whether, in this highly seasonal region, cumulative annual diversity is an oversimplification of well differentiated seasonal communities. Data were obtained through repeated standardised samples collected regularly over an entire year. We clearly identify different summer and winter communities at each site based on species composition and abundance. Seasonal richness and diversity values are different from the cumulative annual values, as a consequence of beta diversity between seasons, and some dung beetle species are identified as idiosyncratic of each particular season. Both ecological (niche partitioning) and biogeographical factors are suggested as drivers of these temporal variations. Thus, because local inventories of fauna that include records over long time periods actually reflect situations where coexistence and interactions are unlikely to occur, highly seasonal sites must be viewed as having temporally differentiated communities in order to reach feasible and reliable baselines for local diversity assessments.