Every ecosystem is shaped by billions of invisible battles: organisms competing for light, nutrients, space, or mates. These competitive interactions determine which species survive, how they evolve, and how vibrant and resilient ecosystems remain. Yet, despite decades of research, scientists have struggled to answer one key question: how competition alters traits, such as body size, lifespan, and behavior, that define how species exist in nature. A global study led by LSU Assistant Professor Jiaqi Tan and published in Nature Communications brings new clarity to that question.