Oribatid mites show how climate and latitudinal gradients in organic matter can drive large-scale biodiversity patterns of soil communities

Aim: The factors determining spatial distributions and diversity of terrestrial inverte-brates are typically investigated at small scales. Large‐scale studies are lacking forsoil animals, which control microbial communities and represent one of the mostdiverse yet poorly known animal assemblages. Here, we analyzed a major group(Oribatida) to test whether belowground macroecological patterns can be predictedby climatic variables, vegetation and large‐scale variation in key soil properties.Location: We modelled the multivariate distribution of more than 100 species usingbiodiversity data collected across Great Britain in the framework of the CountrysideSurvey (http://www.countrysidesurvey.org.uk).Methods: We analyzed species‐level data from 582 samples collected across 162hectads (10×10 km) covering the largest possible range of vegetation types, soilproperties and climatic conditions within GB. We created the first large‐scale mapsof soil animal diversity metrics at the GB scale, including novel estimates of metricsof phylogenetic diversity (PD). Using structural equation modelling, we quantified thedirect and indirect effects of location (latitude, longitude), plant community structureand abiotic factors such as precipitation on species composition, richness and PD.Results: We found that variation in species composition follows a latitudinal gradi-ent with diversity generally increasing northward. The latitudinal variation in speciescomposition drives PD via changes in both species richness and phylogenetic dis-tance between species. This gradient is mostly determined by latitudinal variation inprecipitation and organic matter, which were very good predictors of species com-position. Precipitation and organic matter were, however, relatively weak while sta-tistically significant predictors of diversity metrics.Conclusions: Past studies have emphasized the unpredictability of species distributionsand variation in species composition in hyper diverse soil animal communities. However,past studies were conducted at small scales, where stochastic factors may weaken thesignal of deterministic factors. Oribatid mites in our study show for the first time thatthe large scale latitudinal gradients in climate and organic matter predict not only varia-tion in species composition but also taxonomic and PD of soil animal communities.