Why Does the Gut Have So Many Species? The Paradox of the Plankton in Human Microbial Ecology

The human gut nurtures an exceptionally diverse microbial community, with over a thousand species coexisting despite apparent competition for limited resources. This phenomenon challenges the classical principle of competitive exclusion, drawing parallels with Hutchinson’s ‘Paradox of the Plankton’. Through an ecological lens, this paper examines mechanisms that sustain such high species richness, categorising them into niche-based and neutral processes. Niche differentiation, environmental heterogeneity, evolutionary trade-offs, and microbial interactions create conditions for stable coexistence, while stochastic forces such as ecological drift, migration, and speciation also shape community structure. Furthermore, higher-level selection, influenced by host-microbiome interactions, may play a role in maintaining diversity. A deeper understanding of these processes is crucial, not only for theoretical ecology but also for advancing microbiome-based therapeutic interventions.