13 Predicting Habitat Distribution of the Alien Formosan Squirrel Using Logistic Regression Model Asako MIYAMOTO 1 , Noriko T AMURA 2 , Ken SUGIMURA 1 and Fumio Y AMADA 3 1 Department of Forest Management, Forestry and Forest Products Research Institute (FFPRI) P.O.Box16, Tsukuba Norin Kenkyu Danchi-nai, Ibaraki 305-8687, Japan e-mail: asakom@ffpri.affrc.go.jp 2 Tama Forest Science Garden, (FFPRI), 1833-81, Todori, Hachioji, Tokyo 193-0843, Japan 3 Department of Wildlife Biology, (FFPRI), P.O.Box16, Tsukuba Norin Kenkyu Danchi-nai, Ibaraki 305-8687, Japan Abstract There is growing concern about the impact on the habitat of the native Japanese squirrel (Sciurus lis) in relation to the spread of the Formosan squirrel (Callosciurus erythraeus thaiwanensis), an alien species that was introduced and became naturalized in Kamakura City, Kanagawa Prefecture, in the 1950s. We used a logistic regression model to predict the probability of occurrence of the Formosan squirrel throughout Kanagawa Prefecture. Wooded areas, the proportion of cultivated fields surrounding a wood and the proportion of evergreen trees in a wood, factors that influence the presence of Formosan squirrels, were used as environmental variables in the model. As a result, we found that woods suitable for the Formosan squirrel were distributed not only around Kamakura, which Formosan squirrels currently inhabit, but throughout Kanagawa Prefecture. Furthermore, a comparison of its current habitat and its predicted suitable habitat suggested that the assemblage of large woods along the Sagami River and Sagami Bay would be conductive to increasing its population and expanding its distribution to western Kanagawa. Because there are forests in western Kanagawa which are extensive and are expected to be a suitable habitat for the Formosan squirrel, we should prevent Formosan squirrels from invading the west side of the Sagami River. Key words: alien species, Formosan squirrel, Geographic Information System (GIS), logistic regression model, potential breeding site 1. Introduction The distributions of many species are restricted by factors such as climate, environmental conditions, and geographic limitations. However, humankind has considerably changed the process of natural evolution by relocating countless species of animals. There- fore, today, many species, either intentionally or accidentally, have been introduced into sites that were not their original habitats (Primack & Kobori, 1997). Alien species damage native species and ecosystems on a global scale. Thus, to prevent further loss of biological diversity, we need to study and control the spread of alien species as quickly as possible. Several studies have focused on changes in how alien species affect the number of native species and their habitats (Yamada et al., 1999; Sugimura, 2002). However, most alien species have not been suffi- ciently investigated with respect to effective counte- rmeasures to prevent their intrusion and expansion. The Formosan squirrel (Callosciurus erythraeus thaiwanensis), is an arboreal mammal that originated in Taiwan (Fig. 1). This species was first naturalized in Japan after it escaped from the zoological garden on Izu-Oshima Island, Tokyo, in the 1930s (Udagawa, 1954). After that, it spread throughout Izu-Oshima Island, and was then transported and became estab- lished among several sites such as urban forests, parks and Islands along the Pacific Coast in the western Kanto Region (Fig. 1). The mechanism of its intro- duction to Kanagawa Prefecture is not clearly known: whether some squirrels that were sent to the Enoshima Botanical Garden from Izu-Oshima Islands in 1951 escaped and spread rapidly in Kamakura City, or if squirrels kept as pets in Kamakura City before World War II escaped and became naturalized (Ono, 2001). In Kamakura there are many historic sites where Formosan squirrels are fed by tourists, who admire the animals’ graceful movement. Unfortunately, this species injures garden trees by extensive bark strip- ping and damages houses and telephone cables by gnawing, causing significant economic losses. In Global Environmental Research ©2004 AIRIES 8(1)/2004: 13-21 printed in Japan