When Wolves Were Returned to Yellowstone National Park in 1995

Multiple Choice

When wolves were returned to Yellowstone National Park in 1995, some of the effects noted were increasing levels of berries available to black bears, stabilization of stream banks, increased nesting habitat for birds, and increasing beaver numbers as a result of rejuvenating aspen trees. These were later determined to be the results of reduced numbers and altered feeding behavior of elk as they were preyed upon by the wolves. Given this information, which of the following best describes wolves in Yellowstone National Park?

A) They are a primary consumer.
B) They are an ecosystem engineer.
C) They are a foundation species.
D) They are a keystone species.