The Key Role of Vicariance for Soil Animal Biogeography in a Biodiversity Hotspot Region

ABSTRACT Aim The Indo‐Australian Archipelago is known as a biodiversity hotspot with high levels of endemism typically ascribed to vicariance as reflected by the ‘Wallace's line’. However, it is unknown how vicariance has affected belowground biodiversity, especially process‐based beta diversity. Here, we relate beta diversity of soil oribatid mite (Oribatida, Acari) assemblages to geographic distance as well as climatic and soil factors to explore the factors shaping the diversity of oribatid mites across 11 regions of the Indo‐Australian Archipelago. Location Indo‐Australian Archipelago. Time Period Present. Major Taxa Studied Oribatida, Acari. Methods We compiled a list of 2549 oribatid mite species in the Indo‐Australian Archipelago and investigated the level of endemism and beta diversity of oribatid mites in the 11 regions at species, genus and family level. We then summarised the biogeographical dissimilarity patterns of oribatid mites using ordination and clustering methods and compared the patterns with the zoological boundaries based on aboveground taxa such as Wallace's, Lydekker's, Weber's and Holt's lines. We integrated data on geography, climate and soil to reveal the key drivers of species compositional dissimilarity of oribatid mites among regions using Mantel tests. Results Generally, the level of endemism of oribatid mite assemblages in the 11 regions was high; they formed three groups (west of New Guinea, New Guinea and south of New Guinea) with dissimilarity changing from northwest to southeast. The patterns reflect and integrate the lines of Weber, Lydekker and Holt. Species turnover generally correlated with geographic distance, reflecting the critical role of vicariance in dispersal‐limited oribatid mites. Main Conclusions Our results, for the first time, demonstrate contrasting patterns in below‐ and aboveground organisms in the Indo‐Australian Archipelago, and elucidate how geographic distance‐based vicariance has structured soil animal diversity in this biodiversity hotspot region.