Forest fires and volcanic eruptions are given as examples of factors that are:

1. Some factors strike regardless of how crowded a population is. 2. Density-dependent factors are biological and include predation and competition. 3. The other list covers seasonal and yearly changes in the environment. 4. It also covers natural disasters such as forest fires and volcanic eruptions. 5. Those act on a population without regard to its density. _Source: OpenStax Biology 2e (CC BY 4.0), Ch 45 'Population and Community Ecology', sections 45.1-45.4_