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Difficulty: HardStrengthen

Consider the following argument:

Ecologist: Over the past fifty years, the upper treeline of mountain birch forests in the Scandes range has shifted upward by an average of eighty meters. While many researchers attribute this migration entirely to rising regional summer temperatures prolonging the vegetative growing season, birch seedling survival at the alpine margin is primarily limited by herbivory from mountain hare populations rather than by cold temperatures. Because regional wildlife monitoring records confirm that mountain hare populations in these specific valleys experienced a sharp, sustained collapse starting sixty years ago, this release from seedling herbivory, rather than climatic warming, is the principal cause of the treeline ascent.

Statement: If true, the discovery that in adjacent valleys where mountain hare populations remained stable under hunting bans, the mountain birch treeline did not advance upward over the past fifty years despite experiencing identical increases in summer temperatures, strengthens the ecologist's argument.

Answer: Answer

Answer

True (The supplementary finding strengthens the ecologist's argument by providing a controlled comparison that rules out temperature increases as the sole cause and isolates hare population decline as the operative factor).
The statement is true because the finding functions as a natural control experiment. By showing that in valleys where hare populations did not collapse, identical temperature increases failed to produce treeline advancement, the evidence directly refutes the rival hypothesis that warming alone drove the ecological shift and confirms that the decline in herbivory was an indispensable causal factor.

Step-by-Step Solution

1
Analyze the stimulus structure, identifying premises, competing causes, and the conclusion.
The ecologist concludes that release from hare herbivory, rather than rising summer temperatures, is the principal cause of the 80-meter treeline ascent in the Scandes range.
Deconstructing the causal claim clarifies that the author must defend hare reduction as the operative cause while discounting climate warming as the primary driver.
2
Assess the logical impact of the supplementary statement.
The statement introduces a natural control group: valleys with identical warming but stable hare populations showed no treeline ascent.
In causal reasoning, showing that the effect does not occur when the hypothesized cause (hare decline) is absent, even when the rival factor (warming) is present, strongly reinforces the author's causal attribution.
3
Determine the truth value of the evaluated claim.
Because the supplementary finding directly strengthens the ecologist's conclusion by eliminating a rival explanation and demonstrating causation through a negative control, the claim is True.
Aligns the assessed relationship with standard logical reasoning criteria for strengthen tasks.

Key Concept

Causal strengthening via negative control and elimination of rival explanations
Estimated Time:1m 15s
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Strengthen

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