The modern beetle fauna of Alaska and the Yukon Territory is exceptionally diverse, compared with the faunas of other high latitude regions. The reason for this high level of diversity lies in the Pleistocene history of the region. Unlike almost all other high latitude regions, the lowlands of Beringia remained nearly free of glacial ice during Pleistocene glaciations. Because of this, Beringia served as the only high northern latitude refuge for cold-adapted insects during the Pleistocene. In contrast to this, the arctic and subarctic faunas of Canada east of the Mackenzie delta region were totally extirpated during each glacial interval, as these regions were buried in thick ice sheets. Fossil evidence from the late Tertiary Period suggests that the arctic tundra biome evolved as an ecosystem at that time, and the Beringian sector of the arctic and subarctic has provided habitats for cold-adapted insects since then. One example of the diversity of arctic and subarctic beetles in Beringia is in the ground beetle genus, Pterostichus. Within this genus there is a group of species adapted to cold climates, given the subgenus name Cryobius (Cryo means "cold"). This group has flourished in Beringia. There are twenty-three North American species in this group, and the fossil record indicates that all of them endured Pleistocene glaciations in Alaska and the Yukon Territory. Of the twenty-three species, twelve still only occur in the Beringian region, and eleven have also become established farther east in Canada since the end of the last glaciation. Without the Beringian refuge, it is doubtful that more than a few of these species would have survived the Pleistocene.

Modern Calibration Maps: Maps displaying species presence and X/Y plots displaying the maximum summer temperature and seasonality tolerances for the species.