Cluster dispersal shapes microbial diversity during community assembly

Identifying the drivers of diversity remains a central challenge in microbial ecology. In microbiota, within-community diversity is often linked to host health, which makes it all the more important to understand. Since many communities assemble de novo, microbial dispersal plays a critical role in shaping community structure. While theoretical models typically assume microbes disperse individually, this overlooks cases where microbes disperse in clusters, such as, for example, during host feeding. Here, we investigate how cluster dispersal impacts microbial community assembly, species richness, between-community dissimilarity, and species abundance. We developed a model in which microbes disperse from a pool into communities as clusters and then replicate locally. Using both analytical and numerical approaches, we show that cluster dispersal promotes community homogenization by increasing within-community richness and reducing dissimilarity across communities, even at low dispersal rates. Moreover, it modulates the influence of local selection on microbial community assembly and, consequently, on species abundance. Our results demonstrate that cluster dispersal has distinct effects from simply increasing the dispersal rate. We discuss how these predictions can inform the interpretation of experimental data and demonstrate their utility by reanalyzing a gut microbiota dataset from Caenorhabditis elegans. This analysis reveals new evidence for the role of cluster dispersal in microbial community assembly.