LAUSR

BACKGROUND As an invasive pest from North America, grey squirrels (GS, Sciurus carolinensis Gmelin) are displacing native squirrels in Europe. However, the climatic niche and range dynamics of GS in Europe remain largely unknown. Through niche and range dynamic models, we investigated climatic niche and range shifts between introduced GS in Europe and native GS in North America. RESULTS GS in North America can survive in more variable climatic conditions, and have much wider climatic niche breadth than do GS in Europe. Based on climate, the potential range of GS in Europe included primarily Britain, Ireland, and Italy, whereas the potential range of GS in North America included vast regions of western and southern Europe. If GS in Europe could occupy the same climatic niche space and potential range as GS in North America, they would occupy an area ca. 2.45 times the size of their current range. The unfilling ranges of GS in Europe relative to those of GS in North America were primarily in France, Italy, Spain, Croatia, and Portugal. CONCLUSION Our observations implied that GS in Europe have significant invasion potential, and that range projections based on their occurrence records in Europe may underestimate their invasion risk. Given that small niche shifts between GS in Europe and in North America could lead to large range shifts, niche shifts could be a sensitive indicator in invasion risk assessment. The identified unfilling ranges of the GS in Europe should be prioritized in combating GS invasions in the future.