Abstract
Microbes are widespread in natural ecosystems where they create complex communities. Understanding the functions and dynamics of such microbial communities is a very important theme not only for ecology but also for humankind because microbes can play major roles in our health. Yet, it remains unclear how such complex ecosystems are maintained. Here, we present a simple theory on the dynamics of a microbial community. Bacteria preferring a particular pH in their environment indirectly inhibit the growth of the other types of bacteria by changing the pH to their optimum value. This pH-driven interaction always causes a state of bistability involving different types of bacteria that can be more or less abundant. Furthermore, a moderate abundance ratio of different types of bacteria can confer enhanced resilience to a specific equilibrium state, particularly when a trade-off relationship exists between growth and the ability of bacteria to change the pH of their environment. These results suggest that the balance of the composition of microbiota plays a critical role in maintaining microbial communities.
Highlights
Microbes living in ecosystems create microbial communities and can play key roles in ecosystem functioning [1,2,3,4,5]
The stability of the third equilibrium is independent of the superiority of acidophilic bacteria; rather, it is locally stable when u, u^
When one population of bacteria dominates, the pH is biased to the optimum value of the dominant bacteria, which strongly inhibits the growth of another functional type of bacterium
Summary
Microbes living in ecosystems create microbial communities and can play key roles in ecosystem functioning [1,2,3,4,5]. The stability of three equilibria can change as a function of the strength of pH sensitivity u (see electronic supplementary material, S1). By contrast, when pH sensitivity is low ðu , u^Þ, either one of first and second equilibria becomes unstable depending on the superiority of bacteria, and instead, the third equilibrium becomes stable.
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