Odonate Diversity Patterns in Italy Disclose Intricate Colonization Pathways

Simple Summary During the last Ice Age, most European animals retreated into southern refuges (mainly the Iberian, Italian, and Balkan peninsulas) from which they recolonized central and northern countries after deglaciation. These medio-European territories may have subsequently acted as secondary centers of southward dispersion for many species. Acting both as a refuge and as an area of colonization from adjacent territories, Italy was the theater of complex biogeographical histories, as illustrated by current distributional patterns of odonates (damselflies and dragonflies). These patterns are a result of historical factors and current ecological conditions. Odonates need freshwater for their development, and their richness in Italy decreases southwards, both because of a decrease in precipitation and because of increasing distance from the mainland (peninsula effect). Biogeographical composition of Italian regions is influenced by climate, geographical distances and historical factors. In particular, biogeographical similarities between Italian regions and adjacent areas revealed multiple colonization patterns. After serving as a glacial refuge from which odonates may have colonized medio-European areas, Italy was in turn subject to complex colonization processes, that made its fauna biogeographically very complex, albeit not particularly rich. As a natural bridge between Europe and Africa, Italy occupies a prominent position to understand the biogeography of Europe. The influence of climatic, spatial, and historical factors on current patterns of species richness and turnover (i.e., inter-regional biogeographical differences) has been analyzed for 88 species occurring in 17 Italian natural regions. Use of multimodel inference showed that odonate richness decreased southwards in response to decreasing rainfall, as expected for animals that depend on freshwater for their development. Use of Mantel tests indicated that patterns of inter-regional similarities were influenced by both climate and geographical distances. These patterns, as highlighted using Non-Metric Multidimensional Scaling, indicate a role for historical factors. Biogeographical similarities between Italian regions and adjacent areas revealed multiple colonization pathways. These results, coupled with the overall southward decrease in species richness, suggest that, after serving as a Pleistocene refuge from which odonates may have colonized medio-European areas, Italy was in turn subject to colonization from north to south. This resulted in Italian odonate fauna being less species rich compared to faunas in the medio-European territories, but also being biogeographically very complex.