Differential influences of island biogeographic effects on the diversity of three plant life-forms

Traditional island biogeography has assumed that area size and remoteness are key factors affecting species richness, but this theory has recently been challenged as increased human activity and climate change altered species dispersal patterns. It is unclear whether these two emerging factors will impact the existing mechanisms of biodiversity maintenance. Our research addresses this gap by examining trees, shrubs, and herbs on 30 islands along China's eastern continental shelf. We utilized remote sensing technology to assess human activity, island area and remoteness, and employed various statistical models such as linear regression and PLS-PM to interpret the mechanisms that maintain the richness of different plant life-forms. Our findings show a strong positive correlation between island area and total (SR, R² = 0.51), tree (R² = 0.41), shrub (R² = 0.40), and herb species richness (R² = 0.36, all p < 0.01). Conversely, island remoteness was negatively correlated with SR, tree, and shrub species richness (R² ≤ 0.22, p ≤ 0.01), while no significant correlation with herb species richness. Additionally, we found a positive correlation between human activities and invasive plant species (R² = 0.29, 0.47, p < 0.01). The PLS-PM indicates in addition to island biogeographical effects, climate, human activities, and habitat diversity also affect the distribution of plant diversity through this effect, but the driving mechanisms differ among three plant life-forms. Area is a major determinant for shrub and herb diversity, while remoteness more significantly affects tree species richness. Human activities positively affect tree richness but negatively affect shrub and herb richness. Climatic variables were analyzed to understand their potential effects on the richness of the three plant life-forms. While our results showed a significant positive impact on shrub richness, the relationships with tree and herb richness were not statistically significant. Our study contributes new empirical insights into island biogeography, integrating multiple factors to explain plant diversity maintenance and offering valuable data for island biodiversity conservation.