Which of the following best describes a factor affecting population size when considering food availability?

• A. Biotic availability of food
• B. Abiotic rainfall
• C. Seasonal migration
• D. Biotic access to water

Answer: (A)

Food availability is a key limiter of population size, because populations can grow only if there is enough food for the individuals to eat. The best description is the biotic availability of food—the amount of edible resources produced by living components of the ecosystem, such as plants, seeds, or prey. When these biotic food sources are abundant, populations can increase; when they are scarce, numbers decline. Abiotic rainfall affects food production by influencing how well plants grow, but it is not the food itself. Seasonal migration changes where organisms are at a given time and can affect counts, but it doesn’t directly describe how much food is available. Access to water is essential but is a separate resource, not the food itself. So, biotic availability of food best captures the factor affecting population size through food.