Question

in the yellowstone ecosystem, what factors regulate the size of the elk populations?
top - down factors regulate elk populations.
bottom - up factors regulate elk populations.
neither have a significant impact on elk population size.
in some cases it is bottom - up and in other cases it is top - down regulation.

Explanation:

Elk population regulation in Yellowstone involves both top-down (e.g., wolf predation) and bottom-up (e.g., food availability) factors depending on ecological context.

Answer:

E. In some cases it is bottom-up and in other cases it is top-down regulation.