Divergent responses and regulatory mechanisms of native and alien plant richness on inhabited islands: Biogeography, climate, and anthropogenic disturbance

Alien plant invasions have intensified worldwide throughout the Anthropocene. Nonetheless, how island biogeographic attributes and anthropogenic disturbance differentially regulate native and alien plants on inhabited islands remain poorly understood. Here, we surveyed native and alien plants on 56 inhabited land-bridge islands in the Zhoushan Archipelago, eastern China. Standardized major axis regression (SMA), generalized linear regression, and piecewise structural equation models were employed to disentangle the direct and indirect mechanisms shaping native and alien plant species richness. Our results indicated that species richness of both native and alien plants increased with island area and decreased with island isolation, exhibiting parallel species–area and species–isolation relationships. Native species richness was primarily shaped by island area, mean annual temperature, wind speed, and human population size. By contrast, alien species richness was largely predicted by native species richness and land-use intensity, lending support to the biotic acceptance hypothesis. Island biogeography explained 58.8% and 7.1% of variance for native and alien plant species richness, while anthropogenic disturbance accounted for 17.1% and 22%, respectively. Island area influenced alien plants predominantly through indirect path mediated by native plants, whereas isolation affected native plants both directly and indirectly via wind speed. These findings suggest that classical biogeographic and climatic filters serve as core constraints shaping native plant assemblages, while alien plants are increasingly structured by biotic interactions and anthropogenic disturbances. By integrating island biogeography, climate, and anthropogenic disturbance into a unified framework, this study provides novel mechanistic insights into biodiversity assembly and plant invasion on inhabited islands in the Anthropocene.