Density-independent factors are forces that affect the size of a population of living things regardless of the density of the population. These factors often arise from physical and chemical phenomena such as weather and climate, pollutants in the environment, and natural disasters like fires and hurricanes. They can also include human activities like pollution. Density-independent factors affect the death rates of organisms or have a limiting effect on the population but do not control the number or range of the population of organisms.

In contrast, density-dependent factors are those that strongly affect limiting populations of organisms once it reaches a certain level. These factors include competition, predation, and disease. Density-dependent limiting factors cause a populations per capita growth rate to change, typically to drop, with increasing population density.

In summary, density-independent factors are those that influence the death rates of organisms but do not affect the size, range, or number of the organisms.