Two populations of a species of squirrel are geographically isolated from each other. Although they have the same population density, one population is significantly larger in number than the other. A new bacterial disease, which is easily spread and extremely virulent, affects both populations at the same time.

Which of the following is the best prediction of how the new disease will affect the two populations?

Generally, the smaller the population, the more likely it will be adversely affected by ecological events such as disease. There are several reasons why, but perhaps the primary one is reduced genetic variety in a small population. A larger population, by chance, may have beneficial mutations or variations that confer resistance to a particular disease.

Another thing to consider is the population density. High density population would typically spread diseases faster since individuals will be in close proximity. For this question, the population density is the same, and the disease will spread at a similar rate. Therefore we can simply consider the size of the population only.