Ancient human colonization explains dung beetle species richness in the Mediterranean and Macaronesian islands

The study focused on the islands of the Mediterranean and Macaronesian regions, totalling 147 islands. Islands were included in this study when they had faunistic studies or published records of dung beetle species. The great variability in the environmental features of all these islands maximize the capacity of finding geographical species richness patterns able to be explained by the used explanatory variables and factors. The dung beetle species considered were those belonging to the superfamily Scarabaeoidea, which mainly feed on mammal faeces at any stage of their development. In other words, dung beetles strictly belong to the subfamilies Geotrupinae, Scarabaeinae, and Aphodiinae. However, in our analysis we used data of dung beetles sensu lato because we added data of all the family Aphodiidae, which also includes the subfamilies Psammodiinae, Aegialiinae, and Eremazinae, which have a saprophagous feeding behaviour. Thus, we studied here the geographical variation in the species richness of dung beetle species belonging to Geotrupinae, Scarabaeinae, and Aphodiidae. All available published manuscripts concerning dung beetles in the Mediterranean and Macaronesian regions were compiled, such as atlases, books, peer-reviewed papers, and grey literature. Most of these references come from the authors’ exhaustive library. A total of 362 bibliographic reference sources published from 1838 to 2019 were used to extract dung beetle occurrence data in islands (see Supplementary Material S1 for more details). All these data were checked, and the nomenclature was standardized following an up-to-date taxonomical criterion avoiding subspecies, recent species splitting, and doubtful citations. All dung beetles species finally listed (n = 220) are considered native to the biogeographic region in which the islands studied are located.