BIOGEOGRAPHICAL PATTERNS OF NORTH-AMERICAN HARPALUS-LATREILLE (INSECTA, COLEOPTERA, CARABIDAE)

A study of the fifty-five species of Harpalus Latreille (Insecta: Coleoptera: Carabidae) native to North America north of Mexico shows that the southern Rocky Mountains and associated highlands south of the Wyoming Basin and other adjacent xeric basins are a centre of taxonomic diversity. These mountains and highlands have thirty-one species, the highest diversity for the genus in the continent, and are the major centre of concentration for infraspecific forms and for species endemic to small regions. Twenty-five species occur in an area comprising the northeastern United States and southeastern Canada and twenty-five in an area including the southern portions of Alberta, Saskatchewan and Manitoba. The southeastern United States has only twelve species. The general pattern for sister species is partial or complete allopatry. Western Harpalus shows a pattern of occurring in northern lowlands and southward shifting up into mountains. Present biogeographical patterns result from a mosaic of historical and current ecological factors. The geographical ranges of many species have changed markedly since the Wisconsin. Distribution patterns in most northern regions are due to post-Wisconsin dispersal and current ecological factors. Evolution of new species and infraspecific variation probably resulted from the isolation of ancestral populations in mesic refuges during past periods of dry climate, with the most important such refuges being in southwestern mountains. During glacial periods southern lowland refuges were probably mostly large in area and connected with one another and thus not an important factor for geographical isolation of populations. Data about Harpalus partially contradict Cracraft's (1985) lithospheric complexity hypothesis that differences in biological diversity are explained by varying rates of vicariance and speciation due to lithospheric changes. Conclusions about Harpalus probably applicable to other North American insects occurring in open habitats are: (1) displacement of species ranges up into mountains in xeric southern regions is a common phenomenon; (2) the most common type of geographical disjunction between sister taxa is that between eastern and western vicars; (3) many current North American ranges are post-Wisconsin phenomena; (4) the presence of insects in northern areas other than Beringia is due to post-Wisconsin dispersal; (5) the southwestern mountains of the United States served as an area of mesic refuges where populations underwent taxonomic diversification due to vicariance caused by the spread of xeric habitats across southwestern lowlands; (6) taxa of groups restricted to open habitats probably arose after the Miocene or post-Miocene development of extensive areas of open type plant formations; and (7) taxa of groups restricted to deserts of semi-deserts probably arose after the Pliocene development of such habitats.