Taxonomic variation in levels of endemism: a case study of Italian tenebrionid beetles

Levels of endemism are usually expressed as percentage of endemics among all species recorded in a given area. Endemism levels also vary among taxa, yet inter-taxon variation in endemism levels has received much less attention. We used the Italian tenebrionids to investigate how endemism levels vary among different but related lineages. We evaluated endemism variations among taxonomic levels both as a percentage of endemics to the number of species included in a given taxon (i.e. the tendency of a taxon to produce endemics) and as a percentage to the total number of species (i.e. the importance of that taxon to the overall endemic component). We also considered the residuals of regression lines of endemics against non-endemics. We tested the influence of phylogenetic position, lifestyle, and body size on the percentage of endemics within genera. Use of percentages and residuals gave similar outcomes. Pimeliinae were the subfamily with the highest level of endemism. Erodiini, Pimeliini, Tentyriini, Asidini, Opatrini, and Pedinini were among the tribes with the highest endemism levels. Asida, Pimelia, Tentyria, and Opatrum were the genera with the highest levels of endemism. Phylogenetic position and body size affected significantly endemism levels, with genera including larger species being also those with higher endemism, whereas lifestyle was not significant. This suggests that endemism in the Italian tenebrionid beetles is phylogenetically constrained and that lines including larger species (which are possibly less subject to passive dispersal) tend to be richer in endemics, independently from their lifestyle.