富士山の小哺乳類相-1-哺乳類群集と個体群分布の要因,特に威力競合について

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Three distinct mammal communities were recognized in a forest region on the western slope of Mt. Fuji, Honshu, Japan. Among them, the subalpine conifer forest community is relatively poor both in the number of species and in the density of populations of small mammals and is distinguished from the subalpine deciduous forest community by the absence of Apodemus speciosus speciosus and rarity of Eothenomys kageus. The low mountain mixed forest community is characterized by the presence of Urotrichus talpoides hondonis and the absence of Dymecodon pilirostris. In the most of species found in this region, the habitat range seems to clearly correlate with the nature of forests. However, those of Dymecodon and Urotrichus are exception and seem to be mainly determined by a kind of competition between them. In the region above Shôjiguchi Ni-gôme, 1, 500-2, 380 m alt., the habitat range of Dymecodon was completely confined to an area above and that of Urotrichus mostly to an area below a line at about 1, 600 m alt. in a mixed forest. However, two specimens of Urotrichus were obtained in the habitat range of Dymecodon, one at 2, 380 m and the other at 1, 670 m alt. This indicates that the habitat ranges of these two species are mostly segregated, but the territory of Dymecodon population is not so exclusive as that of Urotrichus and contains several individuals of the latter. Quite same phenomena of such special segregation between these two species have been known from Mt. Hayachine, Tohoku District, and Mt. Yatsugatake, Central Honshu. This can be explained clearly by a following hypothesis. There is a "competition by power" between those two shrew-mole species which are nearly related and similar in general habits including the ecological niche but are slightly different in size and physical strength. So that the individuals of the stronger species, Urotrichus, able to successfully maintain their territories against the individuals of the weaker one, Dymecodon, but the reverse is not true. If the population density of the stronger species is nearly in saturation in an area, then the individuals of the weaker species may be completely driven out from there. But, the stronger species probably able to invade rather freely into the range of weaker species and to live on there. It is probable that Dymecodon, evidently more primitive and older in origin than Urotrichus, had probably covered nearly completely the foot of Mt. Fuji in ancient times. After that Urotrichus had arrived there and gradually drove out Dymecodon from the foot to subalpine region. However in some regions where Urotrichus perhaps had failed to invade by some kinds of barriers, populations of Dymecodon have been maintained well to the present day. A population of Dymecodon at Lake Motosu region, 910m alt., may be such living remnant.
日本哺乳類学会の論文

富士山の小哺乳類相-1-哺乳類群集と個体群分布の要因,特に威力競合について

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