Human disturbance, climate and biodiversity determine biological invasion at a regional scale.

Many factors may affect biological invasion, but their effects have not been quantitatively calculated. Recent studies on the relationship between biodiversity and biological invasion are still controversial. Native biodiversity and alien species diversity are often positively correlated in large-scale observation studies, but negatively correlated in small-scale experimental studies. By using partial correlation and principal component regression methods, we found that human disturbance, climate, native biodiversity and their interactions explained, respectively, 30.3, 34.6, 26.4 and 4.4% of the variation in alien species diversity (ASD) and 50.3, 22.2, 10.8 and 5.5% of the variation in the relative invasibility of alien species (RIA = ASD/native biodiversity) at the regional scale in China. The correlation between ASD and native biodiversity is positive, but the correlation between RIA and native biodiversity is negative. Island and coastal provinces have suffered heavier biological invasions than inland provinces. These findings indicate that biological invasion is mostly determined by human disturbance and favorable climate, but less determined by native biodiversity. A disturbance-dependent niche-vacancy hypothesis is proposed to explain the contradictory observations in large-and small-scale studies.