The term for the proportional representation of species in an ecosystem is species evenness. This concept quantifies how equally individuals are distributed among different species within a community. High species evenness indicates that species populations are balanced, while low evenness suggests dominance by one or few species. This balance is crucial for maintaining ecosystem stability and resilience, as diverse and evenly distributed communities are better equipped to withstand environmental changes and disruptions. Ultimately, understanding species evenness aids in assessing biodiversity and ecological health.