Which statement best describes density-dependent factors?

• A. Their impact increases with population density
• B. They are independent of population size
• C. They are caused by climate extremes
• D. They affect only small populations

Answer: (C)

Density-dependent factors are forces that change how a population is affected based on how crowded it is. When many individuals share the same space, competition for resources becomes fiercer, so growth slows and mortality can rise as food, water, or nesting sites become limited. Disease and parasites spread more easily in close quarters, increasing their impact, and social interactions or mating pressures can also alter survival and reproduction as density increases. In contrast, factors that do not depend on how many organisms are present—such as climate extremes or natural disasters—affect populations regardless of their size. The statement that best describes density-dependent factors is that their impact changes with population density, typically increasing as density rises.