Final answer:
Fire is a true example of a density-independent factor affecting population size, as it impacts populations regardless of their density. Density-independent factors contrast with density-dependent factors, which change their effects based on population density.
Step-by-step explanation:
The statement is true: Fire is an example of a density-independent factor that affects the size of a population. Environmental factors that are density-independent have the same effect on a population's size regardless of the population density. For instance, a forest fire will impact an ecosystem whether the population of a species is large or small because it does not discriminate between crowded and sparse populations. As such, fire can reduce population sizes by destroying habitats and food resources, causing mortality, or forcing migration, but these effects occur regardless of how many individuals of a species are present.
Conversely, density-dependent factors have effects that change with the density of the population. As an example, if a caterpillar population is very dense, the availability of food may become limited, leading to starvation and a subsequent decrease in the population. This effect would be different if the caterpillar population were small since food resources would more likely be sufficient.