Amidst global environmental changes, predicting species responses to future environments is a critical challenge for preserving biodiversity and associated human benefits. We explored the original idea that coral competitive performances, the ability of corals to preempt ecological space on the reef through territorial warfare, serve as indicators of species’ ecological niches and environmental windows, and therefore, responses to future environments. Our surveys indicated that coral performances varied with taxonomic-identity, size, and position along environmental gradients, highlighting complex interplays between life-history, warfare-strategy, and niche segregation. Our results forewarn that growing alterations of coastal environments may trigger shifts in coral dominance, with decline of major reef-building taxa like acroporids, and underscore the importance of restraining human impacts for coastal resilience. Our empirical approach untangles the complexity of species’ battle-like interactions and can help identify winners and losers in various communities caught in the interplay between ecological niches, environmental windows, and global changes.