Which of the following is NOT a density-independent factor?

• A. Hurricanes
• B. Competition for resources
• C. Drought
• D. Fires

Answer: (B)

In population ecology, factors that regulate population size fall into density-dependent and density-independent categories. Density-independent factors affect the population regardless of how many individuals are present—things like weather events or fires. Density-dependent factors change in strength as population density changes, such as competition for limited resources, which becomes more intense as more individuals vie for the same food, space, or mates.

Hurricanes, drought, and fires are classic density-independent factors because their occurrence and impact aren’t caused by how crowded the population is. Competition for resources is the example of a density-dependent factor: as the population grows, resources become scarcer per individual, slowing growth or increasing mortality, etc. Therefore, the factor that is not density-independent is competition for resources.