Climatic niche and range shifts of grey squirrels (Sciurus carolinensis Gmelin) in Europe: an invasive pest displacing native squirrels.

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.