Abstract
A large dominant mole species, Mogera wogura, is progressively expanding its range northwards, displacing a small inferior species, M. imaizumii, in Honshu, Japan. Three of the boundaries where the ranges of the two species abut have been found in the Agematsu region, in the Kitaono region of Shiojiri City, and in the Tatsuno-Suwa region of Nagano Prefecture, central Honshu. The range expansion of M. wogura, however, has been blocked in some areas for long periods. I investigated soil hardness, as one possible factor affecting mole distribution, in habitats on both sides of the boundaries where M. wogura's range expansion has been halted. This investigation clearly revealed that where soft (< 10 kg⁄cm2) soil layers are retained to depths of about 60 cm, or where deep (about 60 cm) soft soil occurs over more than half of the area, M. wogura is able to displace M. imaizumii. In areas where soft soils were shallower than about 60 cm, M. imaizumii was able to continue to inhabit the contact zone, thus soil hardness appears to be an important factor limiting the range expansion of M. wogura.
