Final answer:
A natural catastrophe would be a density-independent factor because its effects occur regardless of a population's density. Density-dependent factors, in contrast, grow in impact with increasing population density.
Step-by-step explanation:
A sudden natural catastrophe resulting in massive die-offs would be categorized as a density-independent limiting factor.
Density-dependent regulation includes factors that are biological and increase in effect as the population density increases. These involve predation, intra- and interspecific competition, accumulation of waste, and diseases such as those caused by parasites. Density-independent factors, however, include events like natural disasters which impact a population regardless of its density. Weather, forest fires, and pollution are examples of such factors. So, despite a natural catastrophe potentially causing a high level of mortality, its impact does not depend on the population density and therefore, it is density-independent.