Narrative (refer to question(s) below): In the Sonoran Desert of the southwestern United States, scientists observed that population clusters of a small cactus were pronounced around nests of desert woodrats. Given this spatial relationship, they began to think the woodrat was related to the seeding of these cactus plants.

After years of counting and observing woodrat nests and nearby cactus plants, scientists collected woodrat droppings for laboratory analysis to determine whether they contained cactus seeds. They also collected the droppings and transported them to other areas to see if this would bring about new population clusters of the cactus.

Scientists then programmed the data they had collected into a computer. A computer program enabled them to predict that increases in the woodrat population would result in corresponding increases in the cactus population, and likewise, a decrease in the number of woodrats would signal an impending decrease in cactus.

Which statement best describes the scientists’ initial observations?

A. Woodrat nests had no apparent effect on cactus populations.

B. The effect of woodrats on cactus plants was different from season to season.

C. Woodrats were spreading cactus seeds and establishing new plant clusters.

D. Woodrats were feeding on the seeds of nearby cactus plants.

E. Cactus plants were more common in proximity to woodrat nests.