著者
鈴木 あいり
出版者
酪農学園大学
巻号頁・発行日
pp.1-34, 2018

Endangered costal plants and insects inhabits in Lower Ishikari River, Hokkaido. However, non-native frog, Japanese toad (Bufo japonicus formosus) was introduced into Asahikawa city in 1980, and it was spread the distribution along Ishikari River Basin recently. The toad was firstly found at lower Ishikari River Estuary in 2005, and the established population was confirmed in 2011. Because this invasive toad preys on the above-ground insects in other areas of Hokkaido, it is believed that costal ecosystem of Ishikari Estuary is facing a serious ecological threaty. This study aims to assess the predation impacts of Bufo japonicus formosus by examining their diet composition. And the breeding season Bufo japonicus formosus capture method use large pitfalls and drift fence. Prey species obtained from stomach contents of Bufo japonicus formosus was classified into 16 families of 13 orders among 5 classes. We observed 291 prey species. Grasshoppers weevil families were the highest stomach content and ants and bees also were composed of stomach content at significant level.11 species of ants od which included seed disposal of costal flowers such as Viola grayi and Formica yessensis, were preyed by the toad. This result might show predation influence and impacts of long-term costal landscape and biodiversity. This study also harvested 1,067 Bufo japonicus formosus from April 16 of 2017 to May 22 with drift-fenced pitfall traps. And there were more harvesting at 2018 (from April 19 of 2018 to May 22) with 2,271 toads 1,445 toads were mark-recaptured; however, onlys 422 (29.2%) were recaptured. . . This 2 years research harvested total of 3,338 Bufo japonicus formosus, and more than 90 % were captured in the short period of time (May 1 May 5). Because this short peak, a breeding season of Bufo japonicus formosus at lower Ishikari River might be shorter than other areas. It's important to conduct continual disinfestation activity using a drift fence and pitfall trap and monitoring investigation in the Ishikari River estuary area where indirect effects on the coastal ecosystem are suggested, from now on and link it to the distribution spread, the number of individuals reduction and explosive increased prevention.

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