Which scenario illustrates a limiting factor affecting population size?

• A. A population of rabbits increases steadily due to unlimited resources.
• B. A boulder blocks the cave entrance.
• C. Sunlight reaches all plants equally.
• D. A drought reduces water availability and slows plant growth.

Answer: (D)

Limiting factors are resources or conditions that prevent a population from growing beyond a certain size. A drought lowers water availability, which is essential for plant growth. With less water, plants grow more slowly or die, reducing the amount of food available for herbivores and, in turn, affecting the whole food chain. This scarcity of a key resource directly caps how large the population can become, illustrating how a limiting factor controls population size. A rock blocking a cave entrance is a physical barrier that might restrict movement rather than directly limiting resources; equal sunlight means resources aren’t being limited; and unlimited resources aren’t realistic, so they wouldn’t curb growth.