Eco-evolutionary dynamics between multiple competitors reduce phytoplankton coexistence but have limited impacts on community productivity

Abstract

Species can evolve rapidly in response to competition but how evolution within communities affects community properties is unclear. To test this, we grew three marine phytoplankton species in monoculture (alone) or polyculture (together) for 17 weeks. We then combined them in communities based on their competition history (monoculture or polyculture isolates) and tracked their composition and productivity over time. We found that species dominance was unaffected, but coexistence was reduced when species evolved together (polyculture isolates). Total biovolume was robust to changes in species relative abundances. However, polyculture isolates had greater oxygen fluxes during exponential phase and were less robust to the addition of an invader. Our results suggest that evolution within communities can strengthen competitive differences between species with uneven effects on different aspects of community functioning. Thus, we should be cautious in extrapolating the consequences of evolution on community biomass to other aspects of productivity or stability.