Fig. 5. Evolution of the plankton community and the fitness landscape through time.

Each panel represents two-dimensional “trait space” of trophic strategy and equivalent spherical diameter (ESD; in micrometers). Background colors (red to blue) describe changes in fitness landscape through time, with height equivalent to biomass-specific net population growth rate. Dots indicate extant populations, with area proportional to population size and color (green to magenta) indicating the balance of autotrophic and heterotrophic nutrition. At year 1, biomass is low and inorganic resources are high, and we see a peak in the fitness landscape centered on fast growing autotrophic cells. By year 2, the population has increased, and a new peak in the fitness landscape has emerged for larger and more heterotrophic traits driven by this potential prey. Over the next 100 years or so, the initial population adapts toward the new fitness landscape peak, with small mixotrophs coexisting with the initial photoautotrophic population. After approximately 100 years, the community has gained sufficient size diversity to begin showing predator-prey dynamics. The evolving community then branches, heading toward the stable coexistence of small phytoplankton, intermediate mixotrophs, and larger zooplankton. At year 5000, it can be seen that there are no remaining positive regions of the fitness landscape, indicative of a community at an ecological and evolutionary equilibrium.