Which of the following is an example of a density-dependent factor?

• A. Forest fire
• B. Weather event
• C. Predation
• D. Pollination

Answer: (D)

Density-dependent factors change in strength as population size changes because their effects hinge on interactions among individuals or with resources that become more limiting at higher densities. Forest fire and weather events are density-independent because their occurrence and impact do not depend on how many organisms are present. Predation is a classic density-dependent factor since predation pressure often grows with prey density, as more prey provide more opportunities for predators. Pollination, however, ties directly to how often pollinators encounter flowers, which increases with the density of flowering individuals and pollinators. More flowers in a given area attract more pollinators and yield higher pollen transfer and seed set, so the reproductive success—and thus population growth—varies with plant density.