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

## TL;DR

This study shows that when phytoplankton species evolve together, they coexist less but maintain similar productivity, with some unexpected effects on oxygen production.

## Contribution

The study reveals that co-evolution among competitors reduces coexistence but has limited effects on overall productivity.

## Key findings

- Species evolving together showed reduced coexistence but similar total biovolume growth rates.
- Polyculture isolates had higher oxygen fluxes during the exponential phase.
- Community biomass was robust to evolutionary changes, but other productivity aspects were affected.

## Abstract

Species can evolve rapidly in response to competition but how evolution within communities affects community properties is unclear. Niche theory predicts that species should evolve to use different resources, increasing coexistence and community productivity. However, recent experiments suggest that species might instead evolve their competitive ability, particularly when competing for essential resources. To test the consequences of species evolution on community properties, we grew three species of marine phytoplankton in monoculture (alone) or polyculture (together) for 4.5 months. We then combined them in communities based on their competition history and tracked community composition and productivity over time. We found that species dominance was unaffected, but coexistence was reduced when species evolved together (polyculture isolates). These species-level changes did not affect community functions equally. Total biovolume growth rates and carrying capacity were the same between communities of monoculture or polyculture isolates but the latter had greater oxygen fluxes during the exponential phase. Our results suggest that evolution within communities can strengthen competitive differences between species with uneven effects on community functioning. While some community properties seem robust to species evolutionary changes, we should be cautious in extrapolating the consequences of evolution from community biomass to other aspects of productivity or stability.