Island Biogeography in the Anthropocene: Natural and Anthropogenic Drivers of Plant Diversity in the Miaodao Archipelago.

Island ecosystems are particularly sensitive to natural and anthropogenic environmental changes, and island plant communities undergo restructuring driven by multiple interacting factors. However, how these factors collectively influence species diversity and community composition on temperate inhabited islands remains unclear. This study assessed changes in vascular plant diversity across spatial gradients of area, isolation, climate, and human disturbance on 10 inhabited islands in Miaodao Archipelago. Based on comprehensive field surveys, we recorded 485 plant taxa and analyzed alpha and beta diversity patterns for different life forms (trees, shrubs, herbs, and invasive plants) using general linear regression, generalized linear models, redundancy analysis, and Mantel tests to identify the primary drivers. We found that island area is the most important predictor of species richness and species distribution. Contrary to classical island biogeography expectations, isolation (distance from the mainland or nearest island) has limited effects on richness, especially under conditions of strong human disturbance. The annual mean wind speed has a positive effect on shrub and herb richness but reduces community diversity and evenness. The human influence index significantly disrupted community structure but did not affect species richness. Beta diversity analysis showed that all plants and trees were driven by both ecological niche differentiation and dispersal processes, while herbs were primarily constrained by dispersal. Our findings indicate that plant communities on temperate inhabited islands are shaped by both natural gradients and human activities, with different plant life forms exhibiting distinct responses. These discoveries underscore the necessity of prioritizing the protection of larger islands and managing human disturbance to maintain biodiversity in coastal archipelagos in the context of global change.