Range Expansion and Food Habits of Rana nigromaculata Introduced to Hokkaido, Japan

Abstract

A field survey was made in 2006 for the exotic black-spotted pond frogs Rana nigromaculata in central Hokkaido, northern Japan. The result suggested a prominent range expansion of this frog since the previous survey in 1997. Examinations of stomach contents from 140 frogs yielded 662 prey items that almost entirely consisted of invertebrate preys, such as lepidopteran larvae, water striders (Gerridae), and spiders (Araneae). The result suggests a fairly little impact, if any, of this accidentally introduced frog upon the native tree frog Hyla jponica through direct predation.