  Why, contrary to theoretical predictions, do marine microbe communities
harbor tremendous phenotypic heterogeneity? How can so many marine microbe
species competing in the same niche coexist? We discovered a unifying
explanation for both phenomena by investigating a non-cooperative game that
interpolates between individual-level competitions and species-level outcomes.
We identified all equilibrium strategies of the game. These strategies are
characterized by maximal phenotypic heterogeneity. They are also neutral
towards each other in the sense that an unlimited number of species can
co-exist while competing according to the equilibrium strategies. Whereas prior
theory predicts that natural selection would minimize trait variation around an
optimum value, here we obtained a rigorous mathematical proof that species with
maximally variable traits are those that endure. This discrepancy may reflect a
disparity between predictions from models developed for larger organisms in
contrast to our microbe-centric model. Rigorous mathematics proves that
phenotypic heterogeneity is itself a mechanistic underpinning of microbial
diversity. This discovery has fundamental ramifications for microbial ecology
and may represent an adaptive reservoir sheltering biodiversity in changing
environmental conditions.
