Mastering Biology Practice Test

Density-independent regulation happens when an abiotic factor changes population size regardless of how crowded the population is. A seasonal drought fits this because it reduces water and resources for everyone in the area, so survival and reproduction decline across the board no matter how many individuals are present. The other scenarios involve density-dependent effects: a disease outbreak that spreads more when populations are crowded because transmission relies on contact rates; increased competition for resources at higher densities because each individual has less access to limited resources as numbers rise; and predator pressure that grows with density since more prey can lead to more encounters with predators. These factors scale with how many individuals there are, which is why they are density-dependent.