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 during the early stages of assembly. 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 species richness, between-community dissimilarity, and species abundance in the initial steps of microbial community assembly. 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. This work reveals new evidence for the role of cluster dispersal in the early dynamics of microbial community assembly.Author summary: Microbial communities, such as those living in the gut, play important roles in host health, yet we still do not fully understand how their diversity is established. In many cases, these communities assemble from scratch, making the way microbes move and colonize new habitats, known as dispersal, crucial for shaping community structure. While most models assume microbes disperse individually, in reality they can travel in clusters, for example, during feeding events. In this study, we explore how cluster dispersal affects the formation and diversity of microbial communities. Using a combination of mathematical modeling and computer simulations, we show that when microbes disperse in clusters, communities become more similar to each other, with higher species richness within each community. Cluster dispersal also changes how local environmental conditions influence which microbes thrive, altering patterns of species abundance. These effects are not simply explained by a higher dispersal rate, highlighting the unique impact of clustered movement.