Question 15

Adult gerbils are far better able to avoid or escape from predators while foraging than are juvenile gerbils.

The explanation for the lower survival probability of parasitized juvenile gerbils compared to nonparasitized ones is strengthened by the fact that adult gerbils have a greater ability to evade predators. This suggests that the combination of being parasitized and having a reduced ability to escape from predators leads to higher mortality in juvenile gerbils.

A) Parasites target adult gerbils more often than they target juvenile gerbils.

This option does not strengthen the explanation for the lower survival of parasitized juveniles. If parasites preferentially target adults, it does not directly address the increased vulnerability of juveniles to predation when parasitized, which is the core issue in the survival probability.

B) Predators that prey on gerbils also typically prey on other, similar species.

While this option provides context about predator behavior, it does not specifically link the predation risk of juvenile gerbils to their parasitized state. Without establishing a direct connection between predation risk and parasitism, this option does not strengthen the explanation regarding survival probabilities.

C) Juvenile gerbils with a greater number of parasites more often die from infections than do those with a smaller number of parasites.

This option suggests a direct correlation between the number of parasites and mortality due to infections. However, it does not address the role of predation in the survival of juvenile gerbils. Thus, it fails to strengthen the explanation focused on predation vulnerability.

D) Adult gerbils are far better able to avoid or escape from predators while foraging than are juvenile gerbils.

This option effectively strengthens the explanation by highlighting that adult gerbils can evade predators more efficiently, which means they may survive despite parasitism. This contrasts with juvenile gerbils, whose compromised ability to escape leads to higher mortality when parasitized, thus directly linking predation risk to the observed survival probabilities.

Conclusion

The correct answer, D, directly supports the explanation for the increased mortality of parasitized juvenile gerbils by emphasizing their reduced capability to escape predators compared to adults. This connection is essential, as it elucidates how parasitism exacerbates predation risk, leading to lower survival rates for juveniles. The other options fail to make this vital link, making them less relevant in strengthening the explanation provided in the passage.