So here we have an example problem that wants us to label each of the following 5 factors that we have numbered down below as either a density-dependent factor using the letter 'd' or as a density-independent factor using the letter 'i'. Now, of course, recall from our previous lesson videos that both density-dependent and density-independent factors will have limiting effects on a population's growth. The difference between these two is whether the impact of the factor depends on population density or not. With density-dependent factors, the impact does depend on population density. But with density-independent factors, the impact does not depend on population density at all.

Keeping that in mind, notice option 1 says, a disease epidemic among the African elephant population. In this case, the disease is the factor, and the question is, does the impact of the disease depend on the population density of the African elephant? The answer to that question is yes; it does depend on it. Because if we were to increase the population density of the African elephant, that would allow the disease to spread faster into more individuals so that the disease has a greater and more significant impact on limiting the population as the population density increases.

So that's consistent with a density-dependent factor, and so we can put a 'd' here. Now next, what we have is a severe flash flood in northern India. In this case, does the impact of the flash flood change with population density? The answer to that is no. The flash flood is going to have the same impact on a population regardless of its density. And so for that reason, we can label this as a density-independent factor.

Next, what we have is number 3, which says an increase in the number of predators that prey on squirrels. In this case, the factor is predation, and looking at these predators and how they impact the squirrels. So the question is, does changing the population density of these predators have an impact on the predation of these squirrels? The answer to that is yes. As we increase the population density of the predators, that's going to increase the predation effect and therefore limit the population of the squirrels more significantly, and so this is a density-dependent factor for that reason.

Next, what we have is severe wildfires in Californian forests during the summer, and the question is, does the impact of the wildfires depend on population density? The answer to this question is no; regardless of what the population density is, the wildfire would have the same impact. And so for that reason, this is a density-independent factor.

Now, last but not least, we have number 5, which says overcrowding at a watering hole in Kenya's Aberdare National Park. In this case, the limiting factor is space, and so we can see here that it's overcrowding. The question is, does the impact of the amount of space depend on the population density? The answer here is yes. It does depend because if we increase the population density, that means there's going to be less space available. And so, that's going to impact or increase the effect of this factor. And so that means it's a density-dependent factor.

This here concludes that example problem, and I'll see you in our next video.