Global species richness of dragonflies and damselflies (Odonata): latitudinal trends and insular colonization.

Odonates are mainly "sun lover" insects, and therefore reach maximum diversity in tropical regions, particularly in rainforests. Here, worldwide patterns of species richness of the order are analysed, by compiling a database of species numbers for 255 continental regions and 243 islands. Area, distance to continents and elevation for all islands were estimated, and their effect analysed on odonate species richness by means of linear models. As expected, a clear effect of latitude and insularity on the species richness of Odonates was found, with a maximum of  550 species in the equator for continental areas but only  200 species in islands. In islands, latitude, area and distance to the continent clearly affect species richness, but elevation had no significant effect. The continental countries with highest richness are Venezuela (548) and Colombia (543 species). Brazil (863) and China (818) have higher richness, but given their size were included in the analysis as states and regions. Excluding very large islands (New Guinea, Sumatra or Borneo), which are considered continents in this paper, Japan (209) is the archipelago with highest richness, albeit Indonesia (737) and the Philippines (306) have more species, but were analysed subdivided by islands. The proportion of Zygoptera found at the different regions was negatively affected by latitude and positively by the area, but not by insularity. In contrast, in islands the proportion of Zygoptera was not affected by latitude, distance or elevation, but was positively affected by area. These analyses highlight the ability of odonates to colonize even the most remote islands, places that can be sources of rapid speciation, as occurred in Hawaii or Fiji.