CoachTwo species compete when they both use a resource — food, light, water, space, nesting sites — whose supply limits their growth. Competition may be by exploitation (each takes what the other would have used) or by interference (direct aggression, toxins, territories). Its outcome follows the competitive exclusion principle: two species that need the same limiting resource in the same way cannot coexist indefinitely in a stable environment; the better competitor eliminates the other. Coexisting competitors therefore differ in niche (niche partitioning) — and where two species overlap they often diverge in form more than where each lives alone (character displacement).
