Which statement best describes density-dependent population regulation?

• A. Growth rate depends on population size.
• B. Growth rate is unaffected by population size.
• C. Regulation occurs only in small populations.
• D. Regulation is driven solely by abiotic factors.

Answer: (A)

Density-dependent population regulation occurs when the growth rate of a population changes as the number of individuals changes, because biotic interactions and resource limitations become more intense at higher densities. As population size rises, competition for food, space, and mates increases; disease transmission and stress can rise, and per-capita birth rates may fall while death rates rise. All of this causes the overall growth rate to slow and eventually level off as the population approaches carrying capacity. That’s why growth rate depends on population size in this scenario, which is the essence of density dependence. In contrast, density-independent regulation would mean the growth rate is set by abiotic factors like weather or catastrophes and does not change with how many individuals are present. The idea that regulation occurs only in small populations or that it’s driven solely by non-biological factors doesn’t fit density-dependent dynamics, which hinge on how population size affects interactions and resource use.