If two species compete for the same limiting resource, what outcome can occur?

• A. Competitive exclusion
• B. Keystone species
• C. Biomass pyramid
• D. Food web

Answer: (A)

When two species rely on the same limiting resource, competitive exclusion can occur: one species that is more efficient at using that resource will tend to dominate, causing the other species to decline in that environment and potentially be driven to local extinction unless they shift to a different niche or partition the resource. This outcome directly reflects how competition for a scarce, shared resource shapes community structure. The other terms describe different ideas—keystone species refers to a species with a disproportionately large influence, a biomass pyramid shows how mass is distributed across trophic levels, and a food web maps feeding relationships—none of which describe the direct outcome of competition for a limiting resource.