Supplementary material from "Half of global islands have reached critical area thresholds for undergoing rapid increases in biological invasions"

Biological invasions are among the threats to global biodiversity and social sustainability, especially on islands. Identifying the threshold of area at which non-native species begin to increase abruptly is crucial for the early prevention strategies. The small-island effect (SIE) was proposed to quantify the nonlinear relationship between native species richness and area but has not yet been applied to non-native species and thus to predict the key breakpoints at which established non-native species start to increase rapidly. Here, based on the extensive global dataset including 769 non-native bird, mammal, amphibian, and reptile species established on 4,277 islands across 54 archipelagos, we detected a high prevalence of SIEs across 66.7% of archipelagos, and approximately 50% of islands have reached the threshold area and thus may be undergoing a rapid increase of biological invasions. SIEs were more likely to occur in those archipelagos with more non-native species introduction events, more established historical non-native species, lower habitat diversity and larger archipelago area range. Our findings may have important implications not only for targeted surveillance of biological invasions on global islands but also for predicting the responses of both non-native and native species to ongoing habitat fragmentation under sustained land-use modification and climate change.