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?
(A) The two populations will be equally affected, because the ability to trigger an immune response is randomly distributed among all squirrels of that species.
(B) The larger population will be less affected by the disease than will the smaller population, because the mutation rate of the larger population is higher than the mutation rate of the smaller population.
(C) The smaller population will be more affected than will the larger population, because the smaller population has less genetic variation than the larger population has.
(D) The smaller population will be less affected than will the larger population, because the smaller population exhibits more genetic drift than the larger population exhibits.

C) The smaller population will be more affected than will the larger population, because the smaller population has less genetic variation than the larger population has.

Explanation:

Genetic variations are present in the natural populations. Some of the genetic traits become adaptive under the changed environmental conditions and allow the individuals carrying them to survive and reproduce. In this way, the genetic variations help to maintain a population.

Therefore, a larger population of a squirrel species with more genetic variations will have less intense impacts of a disturbance/natural calamity and/disease. On the other hand, a smaller population of the same species with a lesser number of squirrels has fewer genetic variations. This population is more likely to be affected in a negative way by a disturbance such as pathogen.