Environment-dependent diversity-stability relationship in microbial communities
Abstract
Understanding the biodiversity–stability relationship has been a central challenge in ecology, yet experiments and theory return contradictory signs: more diverse communities are sometimes more stable, sometimes more fluctuating, and sometimes neither. Here we show that this relationship is not fixed but environment-dependent, by studying bacterial communities under daily dilutions across temperature (10–50 °C) and dilution-rate (10¹–10⁵) gradients. Communities exhibit two distinct fluctuation regimes: collective fluctuations and dominant-species fluctuations. In the collective fluctuation regime, many species interact and fluctuate together, and exhibit a positive diversity-instability relationship and turnover in the most abundant species. In the dominant-species fluctuation regime, only one or a few abundant species fluctuate and exhibit no significant diversity-instability relationship. Single species measurements show that the community fluctuation regime is determined by the balance between species growth and pH-mediated death. We developed a consumer-resource model with pH feedback reproducing both the fluctuation regimes and diversity–stability relationships observed in the experiment. We further tested our theoretical interpretation by performing another experiment tuning the dilution rate to shift between the same two regimes. Our results thus show that two distinct environment-dependent ecological mechanisms and fluctuation regimes lead to different diversity–stability relationships.
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