Biodiversity of marine microbes is safeguarded by phenotypic heterogeneity in ecological traits

while an invariant population at high abundances can be replaced. Again the simulations dis- play the theoretical predictions as shown in Fig 8. The robustness of the equilibrium strategies starkly contrasts the weakness of the invariant strategy, where a population is characterized only by its average competitive ability with no variability about the mean. Remarkably, several strategies can be identified that can replace the invariant strategy as shown in Fig 8, suggesting that the invariant strategy should not persist when other populations of equal mean fitness are present. Thus, a common practice of representing empirical measurements of, for example, microbial physiology as averages may mask the important information of variance in physio- logical capacity. Population size, with exception of very small population size as discussed in (S1 Fig), and duration does not affect these results. Naturally, there are cases where extinctions are observed as shown in (S1 Fig). Our simulations faithfully reproduce the predictions of the competitive exclusion principle [39] when competition involves an overall inferior competitor, characterized by a lower mean competitive ability; see (S1 Fig). Extinctions of equilibrium strategies are observed in cases when the population size is very low (10s of individuals) because equilibrium strategy distributions cannot faithfully be reproduced when few individu- als represent it; see (S2 Fig). This is consistent with chance, rather than selection, dominating

persistence for very small populations. Aside from these explainable deviations, the finding that a maximally-variable distribution of ecological traits will persist in competition has remarkable implications for the ecology and evolution of free living microbes and how we should study them. Maximal intra-specific variability supports unlimited co-existence of spe- cies with equal mean fitness, as demonstrated in a simulation with 100s of populations, all rep- resented by maximally intra-specific strategies as shown in Fig 9. Fig 8. Phenotypic heterogeneity promotes infinite co-existence and thwarts invasion. The uniform distribution, an equilibrium strategy, persists even when their population abudance is vastly lower than their competitor’s. In contrast, the invariant strategy starting at a much higher population is quickly replaced by the Lake Wobegon strategy. Note that the mean competitive abilities of all strategies are identical. https://doi.org/10.1371/journal.pone.0254799.g008 PLOS ONE Biodiversity of marine microbes is safeguarded by phenotypic heterogeneity in ecological traits PLOS ONE | https://doi.org/10.1371/journal.pone.0254799 August 4, 2021 11 / 18