Abstract
Symbiotic relationships between microbes and hosts frequently involve the assembly of complex microbial communities. Community‐level patterns influence life‐history traits, ecological trajectories of partners, and are often critical for host health. These patterns are driven by mechanisms acting at the individual level, including microbial dispersal, host selection, and microbe–resource interactions. Critically, we still lack a clear picture of how these mechanisms interact to shape microbiome assembly. We present a model that describes how distinct community structures arise from those underlying mechanisms. To illustrate the approach, we simulate microbiome data from marine sponges, thereby bridging mechanistic models and empirical patterns. We further apply the model to human data to explore its relevance across systems, proposing that a small set of general mechanisms may govern diverse patterns of diversity and abundance. Our findings advance ecological theory by linking individual‐level processes to community‐scale patterns, illuminating key drivers of microbiome assembly.