Final answer:
Competition for food is an example of a density-dependent factor because its effects on a population vary with the population's density; as density increases, competition for food leads to greater impacts on mortality and reproduction.
Step-by-step explanation:
Among the options listed, B. Competition for food is an example of a density-dependent factor. Density-dependent factors are conditions that have varying impacts on a population depending on its density. For instance, as the population increases, competition for limited resources such as food intensifies, which in turn can lead to a decline in the population as individuals compete for those scarce resources. This will affect the mortality rate, the reproductive success, and the overall rate of population growth.
Conversely, density-independent factors, such as natural disasters or temperature fluctuations, affect the population irrespective of its size. An example is a flood that destroys the habitat of a species: it will have roughly the same impact on the population whether there are few individuals or many.