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Difficulty: EasyCommand of Evidence: Textual

Ecologist Dr. Elena Rostova hypothesized that the reintroduction of gray wolves (*Canis lupus*) to a national park indirectly benefits the local beaver (*Castor canadensis*) population. Rostova suggests that wolves preying on elk (*Cervus canadensis*) reduces elk grazing on young willow trees. Since beavers depend on willow trees for food and building materials, a reduction in elk grazing should allow willow stands to recover, facilitating a rise in beaver numbers.

Which finding, if true, would most directly support Rostova's hypothesis?

  1. A
    The diet of wolves in the park consists primarily of elk, though they also occasionally hunt smaller mammals.
  2. B
    National parks that did not reintroduce wolves saw no change in their elk populations during the study period.
  3. Following the reintroduction of wolves, willow canopy cover in the park increased, and the beaver population subsequently expanded.Answer
  4. D
    Beavers in the park also consume other woody plants, such as aspen and birch, when willow is scarce.

Answer

The finding that following the reintroduction of wolves, willow canopy cover in the park increased, and the beaver population subsequently expanded.
The correct answer directly supports the hypothesis by showing that the reintroduction of wolves was followed by the predicted outcomes: an increase in willow density and a subsequent expansion of the beaver population. This establishes the indirect ecological benefit outlined in the passage.

Step-by-Step Solution

1
Identify the core hypothesis proposed in the passage.
The hypothesis states that reintroducing wolves will lead to fewer elk, which leads to willow recovery, which ultimately benefits the beaver population.
To evaluate supporting evidence, the logical chain of the hypothesis must be clearly understood.
2
Evaluate each option to see which one provides evidence for the link between wolf reintroduction, willow recovery, and beaver population increase.
The finding showing that willow cover increased and beaver populations grew after wolves were reintroduced directly demonstrates this causal chain.
A supporting evidence question requires an option that confirms the predicted relationship between the variables.

Key Concept

Command of Evidence: Textual
Estimated Time:1m 0s
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Command of Evidence: Textual

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