In 1995 the United States National Park Service reintroduced wolves into Yellowstone National Park, from which they had been eliminated decades before by overhunting. Biologists hoped the reintroduction would return the park's mix of animals to a more natural state. After the wolves disappearance, the population of their onetime prey, the elk. had burgeoned. Subsequently, new tree growth declined as multiplying elk browsed young trees, denuding certain areas of the park. Following the wolves" return, the elk population declined and young trees rebounded. Most scientists attribute the vegetation changes to the wolves1 return. However. Ration observes that Yellowstone has not had a harsh winter since wolf numbers reached high levels and suggests that elk may not have needed to resort to trees for food.

It can be inferred from the passage that the scientists would he most likely to cite which of the following in support of their view?