GIS analysis of the biogeography of beetles of the subgenus Anisodactylus (Insecta: Coleoptera: Carabidae: genus Anisodactylus)

The advent of GIS technology and the World Wide Web, respectively, facilitate analysing geographical relationships and electronically storing and exchanging biogeographic data. This paper illustrates GIS technology with a study of the subgenus Anisodactylus Dejean (Insecta: Coleoptera: Carabidae: genus Anisodactylus). Species are concentrated in three centres of biodiversity in North America and in four in lands near the western Mediterranean. These centres largely correspond to current areas of wetlands. Eurasia has fewer species than expected based on its area, probably because large portions have habitats unfavourable for the subgenus and/or are poorly collected for Carabidae. Members of the subgenus are primarily adapted to areas with January temperatures between ?10 and 10 °C, July temperatures from 10 to 30 °C and mean annual precipitation from 20 to 200 mm. Cold is apparently a major limiting factor because it typically occurs during several consecutive months of winter and is difficult to escape except by hibernation. Heat is less of a stress when moisture is sufficient. The size of geographical ranges is often larger in the North than in the South and correlates with the latitude of the centre of ranges at r =0.42 (level of significance=0.05). Geographic ranges are often smaller in western North America and in the western Mediterranean than elsewhere in the Northern Hemisphere. Explanations for the smaller sizes include portions of western North America having unfavourable desert or montane habitats, the Rocky Mountains and deserts barring eastward dispersal of species, and the smaller size and more patchy distribution of climatic zones and habitats. In North America geographical ranges west of the Rocky Mountains are north–south elongated because they track primarily north–south orientated climatic zones and because mountains and deserts bar eastward extension. Ranges in north-eastern and north-central North America tend to extend east–west along temperature isotherms. In Eurasia many ranges are stretched east–west because of the shape of the continent and because many northern and southern areas lack suitable habitats. Species with relatively high numbers of apomorphic character states cluster in western Eurasia and to a lesser extent in western North America. The North American centres of biodiversity are post-Wisconsin phenomena while those near the western Mediterranean probably date from the Oligocene or Miocene.