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

faithfully reproduces the ‘competitive exclusion’ principle [39], and the species with the lower mean is eliminated. (TIF) S2 Fig. Low population abundances may not reproduce phenotypic heterogeneity. On the left, the nominally uniform distribution goes extinct when the uniform distribution is statisti- cally poorly characterized because few individuals represent the distribution. The right shows the mean competitive ability of the two cohorts in this simulation. The inferior mean in time step 3 results in extinction of the blue type. Even a reversal of fortunes in the next time step, with a higher mean CA for blue than orange does not balance the competition, and the blue population is eliminated. The blue-uniform strategy could have persisted longer by chance alone, but the randomly selected orange competitors all had superior competitive ability due to low population abundances. The trivial example of competition with an inferior competitor, characterized by a lower mean competitive ability, leads to extinction as shown in S1 Fig. At low population sizes the underlying strategy distributions can be poorly represented, especially for the maximally variable uniform distribution as shown in S2 Fig. In these cases, extinctions can be observed. Such dynamics would apply when few individuals colonize a new habitat, mutations yield new functions or other events when a few individuals represent the entirety of the population. (TIF) S1 Appendix. Mathematical proofs for the discrete model. (ZIP) S2 Appendix. Mathematical proofs for the continuous model. (ZIP) Acknowledgments

We thank C.-J. Karlsson and B. Chen for providing constructive criticism on a preliminary draft of this manuscript and H. McNair and P. Marrec for help with the figures. Insights pro- vided through the review process helped to improve the quality of the manuscript, for which we are very grateful. Author Contributions Conceptualization: Susanne Menden-Deuer, Julie Rowlett. Formal analysis: Susanne Menden-Deuer, Julie Rowlett. Funding acquisition: Susanne Menden-Deuer, Julie Rowlett. Investigation: Susanne Menden-Deuer, Julie Rowlett. Methodology: Susanne Menden-Deuer, Julie Rowlett. Validation: Susanne Menden-Deuer. Visualization: Susanne Menden-Deuer, Julie Rowlett. Writing – original draft: Susanne Menden-Deuer, Julie Rowlett, Medet Nursultanov. Writing – review & editing: Susanne Menden-Deuer, Julie Rowlett, Medet Nursultanov, Sinead Collins, Tatiana Rynearson. 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 15 / 18