Question

prior to 1995, gray wolves (canis lupus) had been absent from yellowstone national park for nearly 70 years. grey wolves prey on large herbivores like deer, elk, moose, bison, bighorn sheep, caribou, and musk oxen. during this time, the elk population had grown significantly, as there were fewer predators to control their numbers. this increase in elk led to overgrazing, particularly of young willow and aspen trees that grow near river banks, which in turn affected other species that depended on these plants for food and shelter. without the willow and aspen trees, erosion of the river banks increased, lowering the water quality. how will the ecosystem respond to the gray wolves being reintroduced? chose all correct answers that apply.

the biodiversity of the yellowstone ecosystem will decrease because wolves eat large herbivores as prey.

bird populations near the river will increase because there is more shelter in the trees.

the willow and aspen tree populations will increase because there are fewer elk to graze on them.

the elk population will decrease because wolves will hunt elk for food.

Explanation:

• The elk population will decrease because wolves will hunt elk for food: When wolves are reintroduced, they act as predators. Elk are part of their prey base. An increase in wolf population (due to re - introduction) would lead to more elk being hunted, thus reducing the elk population.
• The willow and aspen tree populations will increase because there are fewer elk to graze on them: Elk are herbivores that graze on willow and aspen. With a decrease in elk population (due to wolf predation), there is less grazing pressure on these trees. So, their populations can increase.
• Bird populations near the river will increase because there is more shelter in the trees: As willow and aspen trees (which are near the river) increase in number (due to less elk grazing), they provide more shelter. Birds can use these trees for nesting, roosting etc., so their populations increase.
• The biodiversity of the Yellowstone ecosystem will decrease because wolves eat large herbivores as prey: This is incorrect. Re - introduction of wolves actually increases biodiversity. Wolves control herbivore (like elk) populations. This allows for a more diverse plant community (as seen with willow and aspen increase). A more diverse plant community supports a more diverse community of other species (like birds, insects etc.).

Answer:

The elk population will decrease because wolves will hunt elk for food, The willow and aspen tree populations will increase because there are fewer elk to graze on them, Bird populations near the river will increase because there is more shelter in the trees.