“Land Emergence” and “Elevation Shift” Affect Diversification: A New Perspective Toward Understanding the High Species Diversity of Terrestrial Animals in Japan

Abstract

Animal species in Japan are characterized by a high degree of endemism. Recent phylogeographic studies have revealed interesting and unexpected patterns of diversification in the islands adjacent to the main Japanese islands (Hokkaido, Honshu, Shikoku, and Kyushu) and the within-island diversification in the main islands. In this chapter, I propose two potential models to explain such diversification: 'land emergence' effects and 'elevation shift' effects, based on changes in animal distribution in response to climate or habitat alteration during the repeated glaciation and post-glaciation periods in the Pleistocene era. In the land emergence effect, population expansion and contraction in response to land emergence and disappearance contributed to the dynamic changes in morphological and genetic characters in the four main islands and their adjacent offshore islands. In the elevation shift effect, 'cryptic barriers' and 'cryptic corridors' were formed through elevation shifts in response to climatic changes in the past. The effect also contributed to the formation of diversification patterns among the low elevation species. For further understanding of diversification of Japanese animals, both land emergence and elevation shift effects should be evaluated for each species, with careful consideration of the 'connectivity' of animal dispersal.