野鼠類の種間関係の研究I : すみわけの変遷

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There occur three species of murids, Clethrionomys rufocanus ledfordiae, C. rutilus mikado and Rattus noroegicus, in the small tree stand near the farmstead of the Hokkaido University. These species do not intermingle spatially, but each of them has its own habitat. It seems probable that the natural condition of their habitat is not associated strictly with the occurence of each species. In 1951,from spring to summer, each species had approximately equal size of population and segregated spatially. In summer, as many as possible of the murid inhabitants of the area were removed and then about the same number of pairs of each C.r. mikado and C.r. bedfordiae were immigrated to the area from the peat-bog field of Nopporo, near Sapporo. Two immigrant populations occupied the area respectively, keeping the same spatial relation as the predecessors in spring. Furthermore they spread over the place which had formerly been occupied by R. norvegicus. In 1952,no observation was made. In 1953,from spring to autumn, C.r. bedfordiae was found abundantly and C.r. mikado was depressed spatially, while R. norvegicus occurred in small numbers at one part of the area, which in 1951 were inhabited by C.r. mikado. In 1954,C.r. bedfordiae became more abundant, occupying a larger area than in 1953,while C.r. mikado was much more depressed moving its habitat slightly. R. norvegicus recovered its population size slightly in the same place as in 1953. In 1955,C.r. bedfordiae decreased in number and rather concentrated at the center of the area, while R. norvegicus became very abundant and covered the whole area except the central portion. C.r. mikado hardly kept its population within the babitats of the others. In spite of the changes of the population sizes and the relative positions of the habitats, three species did not intermingle thoroughly, and even a small population concentrated spatially. During these process of changing spatial relation among the murids, the conditions of the tree stand showed no marked change. In short, from these observations we can conclude that the changes of the habitat is due to the fluctuation of the population, however the cause of which has not been acertained. The theory of "Sumiwake"(habitat segregation by IMANISHI 1941,or ecological segregation)is now being earnestly discussed by Japanese ecologists, As the mechanism of "Sumiwake", some authors emphasize the result of habitat selection according to the life form of the species, while others postulate the interaction between the species. The result of the present observations on the murids may support the latter view.
日本生態学会の論文
1956-03-31

野鼠類の種間関係の研究I : すみわけの変遷

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