What drives study-dependent differences in distance-decay relationships of microbial communities?

Aim: Ecological communities that exist closer together in space are generally more compositionally similar than those far apart, as defined by the distance-decay of similarity relationship. However, recent research has revealed substantial variability in the distance-decay relationships of microbial communities between studies of different taxonomic groups, ecosystems, spatial scales, as well as between those using different molecular methodologies (e.g. high-throughput sequencing versus molecular fingerprinting). Here, we test how these factors influence the strength of microbial distance-decay relationships, to draw generalisations about how microbial β-diversity scales with space. Location: Global. Time period: Studies published between 2005-2019 (inclusive). Major taxa studied: Bacteria, Archaea, and microbial Eukarya. Methods: We conducted a meta-analysis of microbial distance-decay relationships, using the Mantel correlation coefficient as a measure of the strength of distance-decay relationships. Our final dataset consisted of 452 data points, varying in environmental/ecological context or methodological approaches, and used linear models to test the effects of each variable. Results: Both ecological and methodological factors had significant impacts on the strength of microbial distance-decay relationships. Specifically, the strength of these relationships varied between environments and habitats, with soils showing significantly weaker distance-decay relationships than other habitats, whilst increasing spatial extents had no effect. Methodological factors such as sequencing depth were positively related to the strength of distance-decay relationships, and choice of dissimilarity metric was also important, with phylogenetic metrics generally giving weaker distance-decay relationships than binary or abundance-based indices. Main conclusions: We conclude that widely studied microbial biogeographic patterns, such as the distance-decay relationship, vary by ecological context but are primarily distorted by methodological choices. Consequently, we suggest that by linking methodological approaches appropriately to the ecological context of a study, we can progress towards generalisable biogeographic relationships in microbial ecology.Missing values are coded as NA. Funding provided by: Natural Environment Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000270Award Number: 471757Please see associated manuscript for all relevent details about dataset collection