著者

斎藤 和範 八谷 和彦

出版者

「野生生物と社会」学会

雑誌

野生生物保護 (ISSN:13418777)

巻号頁・発行日

vol.7, no.2, pp.67-74, 2002-03-29 (Released:2017-10-18)

参考文献数

16

被引用文献数

4

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The Tokyo Daruma Pond Frog (Rana (Rana) porosa porosa) was assumed to have invaded from Honshu into Hokkaido before the 1990's (Saito et al.1998). However, it has become clear that the distribution of this pond frog is even now restricted to a small paddy area around Iwamizawa in central Hokkaido. Population density was high especially at old style paddy fields and shallow earth ditches. The restricted distribution of the pond frog could be related to the following: 1) As a result of field improvement, irrigation and drainage systems were changed from shallow earth brooks and ditches to deep, concrete-sided ones whose walls are too high for pond frogs to jump over; 2) Weeding out of footpaths around paddy fields and canals resulted in a decrease of food insects for the frogs; 3) Improvement of paddy field drainage limited the pond frog habitat after the irrigation season. Fortunately, paddy field improvement is considered an effective barrier of distributional expansion of pond frogs whose habitat was earthen brooks and ditches. It is ironic that the invasive frogs' activity is restricted by unnatural artificial paddy field improvements.