Which factor is a common limiting factor for population growth in many ecosystems?

• A. Food availability
• B. Sunlight
• C. Color of leaves
• D. Distance from water

Answer: (A)

Limiting resources regulate how big a population can get. Food availability is a common limiting factor because energy from food powers every individual's growth, maintenance, and ability to reproduce. When there isn’t enough food, survival and reproduction drop, so the population can’t grow beyond what the available food can support. This creates a carrying capacity tied to how much food is available in the environment.

Sunlight matters in some ecosystems where light limits primary production, but it isn’t universally the bottleneck for population growth. The color of leaves has no direct impact on how many individuals an environment can support, and distance from water only constrains populations in specific contexts. So food availability best explains why population size is limited across many ecosystems.