Taxonomic evenness–area relationships for plant and soil microbes on tropical islands: patterns and potential mechanisms

Island area is widely known to affect taxonomic richness across different trophic levels. However, the impact of island size on taxonomic evenness, which quantifies the species abundance distribution, has yet to be explored, especially in tropical island ecosystems. In this study, twenty representative tropical islands with areas ranging from 2 ha to 406 ha and minimal human disturbance were selected. Then we measured the taxonomic evenness of aboveground plants, belowground soil bacterial and fungal communities, as well as a series of soil properties (i.e. pH, salinity, organic carbon, total nitrogen, total phosphorus, total potassium and carbon/nitrogen ratio). We found that, like the positive area‐richness relationship, the taxonomic evenness of the plant community also increased with island area, indicating more stable plant communities on the larger islands. However, the island area did not affect the taxonomic evenness of soil bacterial and fungal communities. Furthermore, the effects of island area on the taxonomic evenness of the plant and soil bacterial communities were mediated through soil factors (e.g. soil pH and salinity). Together, the contrasting area–evenness relationships among plant and soil microbe groups highlight the importance of dissecting potential mechanisms underlying community dynamics of different organisms.