野鼠類の種間関係の研究 : III. 小林地におけるすみわけ

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In the first report of this series of study (OTA and TAKATSU 1956), we described the changing process of habitat segregation of three species of the Muridae, Clethrionomys rufocanus, C. rutilus mikado and Rattus norvegicus in a small tree stand, and we discussed mechanism of habitat segregation. In that paper we emphasized the interaction of populations rather than the habitat selection as the main cause of habitat segregation. But the conclusion of the first report was found to be partly in need of reconsideration. I shall describe some aspects of the habitat segregation of the three species of murids in the first year of the study, and correct and supplement the conclusion of the previous paper. In the small tree stand described previously, C. rufocanus, C. rutilus and R. norvegicus live together and separately. The former two are related closely, but the latter is not only a distant ally of the formers but sometime a facultative predator of them. In spring, when each population density was low, each lived separately in the survey area. Toward summer, as each population grew large, the distributions of the three species were overlapped, but each had its own denser populated area. Although the occurrence of each species was not strictly associated with the conditions of the area, generally speaking, C. rufocanus occupied the open-dry part, C. rutilus the shaded-wet part and R. norvegicus the sides of the river and the drainage. As described in the first paper, a field experiment was done in summer to determine the cause of the habitat segregation. The populations of the two species of Clethrionomys were transplanted to the area from the other place after removing the former inhabitants. The two immigrant populations settled in the area separately. Similar to the former inhabitants, C. rufocanus occupied the open-dry part and C. rutilus occupied the shaded-wet part of the area, further both exploited the vacant site which was formerly occupied by R. norvegicus. R. norvegicus was not transplanted, but many new individuals of it appeared on the outside of the drainage around the area, and very few of them appeared on the inside of the drainage. Thus, the habitat segregation became clearer in this time than in spring. From the result of this experiment, it should be concluded that the habitat segregation of the two species of Clethrionomys is due to habitat selection and the habitat segregation between R. norvegicus and Clethrionomys is due to interaction (competition). But at the same time, interaction was also found between the two species of Clethrionomys because some replacements and interminglings of individuals were seen between their occupations of habitat, and the habitat selection of R. norvegicus was also found because the rats always occurred along the river and the drainages. Toward autumn, the populations of two species of Clethrionomys declined and they showed no segregation in the area, while the population of R. norvegicus grew large on the outside of the area and a few rats went into the inside. The rats were foraging crops of the field around the area. This type of segregation between R. norvegicus and Clethrionomys is certainly due to habitat selection. Habitat selection and interaction are two aspects of habitat segregation and they act in combination, and which of them acts mainly is determined by the intrinsic and extrinsic conditions of the species. Furthermore, in the lives of higher animals, psychological factors may be effective to habitat selection and interaction. Two different cases of co-existence were observed in this area. The one was found in the time of population growths of the three species and the other was found in the time of population declines of the two species of Clethrionomys. The former case is commoner than the latter and it is usually interpreted as a process of competition. The latter case cannot be considered as competition, and it is postulated as a process of disolution of inters
日本生態学会の論文
1958-12-30

著者

太田嘉四夫
北海道大学農学部動物学教室

野鼠類の種間関係の研究 : III. 小林地におけるすみわけ

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