Microbial Community Assembly Rules Emergent from the Stable Marriage Problem*

A central debate in microbial ecology asks whether resource habitat or species interactions are more important in determining community composition. Recent surveys point towards habitat filtering as the key factor: naturally co-occurring microbial species tend to metabolically compete with each other. How does this competition not result in the exclusion of all but the most dominant species? We show that modeling microbes as sequential consumers of resources in the vein of the well-studied stable marriage problem can help resolve this apparent paradox. Complementarity in resource prioritization (hierarchical diauxic shifts) in our model allows multiple metabolic competitors to robustly coexist with each other. In addition to this, our model exhibits several interesting properties common to microbial consortia: specifically, multiple stable states and community restructuring in response to external perturbations. Our results are relevant to the understanding of polysaccharide utilization patterns by microbes residing in the human gut.