Diversity and interaction predict microbial community dynamics

By observing miniature microbial ecosystems, researchers show that more complex ecological communities – those with greater diversity and stronger interactions – tend to be less stable over time and transition between distinct dynamical phases, according to a new study. The findings offer insights into general ecological principles and demonstrate predictable patterns of diversity and dynamics in ecological communities. Ecological communities of all shapes and sizes – from our own individual microbiomes to Earth’s rainforests – often host high numbers of coexisting species, which together serve important functions. However, such communities are complex and their dynamics are difficult to predict, and studying these relationships in large-scale ecosystems is generally unfeasible. As a result, key aspects of ecosystem functioning, like whether the diversity of a community enhances or weakens its stability, remain poorly understood. Using mathematical modeling and observations of bacterial communities under highly controlled conditions, Jiliang Hu and colleagues performed a direct test of ecological theory predicting that simple community-level features, such as diversity and interaction, dictate community behaviors. Hu et al. found that more complex bacterial ecological communities were less stable over time and evolve differently, yet predictably, depending on their initial diversity and the interaction strengths among the various species. The authors demonstrate that communities shift through distinct phases as diversity or interactions increase, from a stable equilibrium where all species coexist to partial coexistence to persistent and dynamic fluctuations in species abundances. According to the findings, communities that fluctuated tended to maintain higher species richness, suggesting that diversity and stability reinforce one another. “Overall, the findings of Hu et al. suggest that ecological communities generally transition through distinct phases as interspecies interaction strength or diversity changes, similar to how matter transitions abruptly though distinct states when temperature or pressure changes,” write Matthias Huelsmann and Martin Ackermann in a related Perspective.