Climate change is a key driver of species evolution. Biodiversity change often accompanies environmental changes, but it is unclear how species diversity affects the evolution of species within a community and the functioning of the community itself. We used marine phytoplankton to empirically assess the consequences of competition history on species and community evolution. To do this, we assembled communities of three species that evolved either alone or together for 4.5 months (~140 generations). We tracked the assembly and functioning of these communities for 20 days. We found that competition history did not alter the growth patterns of either community. Furthermore, the species did not show any morphological variability which could be related to their coevolution. Nevertheless, we found a reduced coexistence in the Co-evolved communities, suggesting that coevolution increased rather than decreased competition. Character divergence is not always possible, particularly if species compete for essential resources as in the case of phytoplankton. Despite their lower evenness, coevolved communities showed an increase in metabolic productivity during the exponential growth phase. The species traits that gave way to this metabolic response are still unclear, but this result suggest that biomass and metabolic energy might not necessarily follow the same evolutionary trajectories.
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