Evolutionary adaptation to steady or changing environments affects competitive outcomes in marine phytoplankton

Abstract The interplay of phytoplankton competition and adaptation affects how phytoplankton, and ultimately marine ecosystems, respond to global warming. However, current ecosystem models that are run under global warming scenarios do not include both processes simultaneously. To fill this gap, we developed an innovative ecosystem model for the Baltic Sea that simulates competition between three phytoplankton functional groups and allows for adaptation to changing temperatures. As adaptation can be affected by the resuspension of dormant resting cells from the sediment, we explicitly implemented this mechanism. We found that resuspension tends to slow down adaptation, and that competition and adaptation influence each other. The outcome of the competition‐adaptation interplay depends on environmental conditions. In a steady environment, competition drives adaptation to individual temperature niches to reduce competition pressure. In a changing environment, adaptation allows inferior competitors to mitigate the dominance of preadapted superior competitors. Our results demonstrate that by neglecting adaptation, models can systematically overestimate warming‐related changes in taxa dominance. Ecosystem models should include both competition and adaptation to accurately simulate phytoplankton responses to global warming. Our model is ideally suited to integrate emerging evolutionary data based on long‐term data series (e.g., from sediment archives) to further improve projections of future ecosystem change.