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Difficulty: MediumIdentifying Underlying Assumptions

Forest ecologists observed that high-altitude pine trees infected with a native bark beetle species synthesize elevated levels of terpene resins, which effectively deter beetle oviposition. To protect commercial pine plantations at lower elevations from seasonal beetle outbreaks, the ecologists plan to treat young trees with a synthetic plant hormone that induces high terpene resin production prior to beetle emergence. They conclude that implementing this hormone treatment will significantly decrease beetle infestation rates in commercial plantations without relying on chemical insecticides. Which of the following is an assumption on which the forest ecologists' plan depends?

  1. The bark beetle populations in lower-elevation commercial plantations are not significantly more tolerant of terpene resins than the beetle populations in high-altitude forests.Answer
  2. B
    Applying chemical insecticides to commercial pine plantations causes cumulative soil toxicity that inhibits long-term tree growth.
  3. C
    Beetle infestation rates in high-altitude forests have historically been lower than infestation rates in low-elevation plantations.
  4. D
    Treating commercial pine trees with the synthetic hormone is less expensive per acre than applying conventional chemical insecticides.
  5. E
    The synthetic hormone can be manufactured in sufficient supply to treat every commercial pine plantation across the entire geographic region.

Answer

The argument assumes that bark beetle populations in lower-elevation commercial plantations are not significantly more tolerant of terpene resins than high-altitude beetle populations.
The argument relies on the premise that stimulating terpene resin production in commercial pine trees will deter beetles from laying eggs. For this plan to succeed, the lower-elevation beetles targeted by the intervention must actually be susceptible to the deterrent effect of terpene resins. If lower-elevation beetles were highly tolerant of terpene resin, the hormone treatment would fail to prevent infestation, shattering the conclusion.

Step-by-Step Solution

1
Deconstruct the argument structure
Premise: High-altitude pine trees produce terpene resins that deter beetle oviposition. Plan: Apply a synthetic hormone to lower-elevation commercial trees to induce terpene resin production before beetle emergence. Conclusion: The treatment will significantly reduce beetle infestation rates in commercial plantations.
Identifying premises and the core conclusion establishes the logical gap that an underlying assumption must bridge.
2
Identify the unstated logical gap
The argument assumes that the deterrence observed in high-altitude forests will transfer effectively to low-elevation commercial plantations.
The plan relies on low-elevation beetles responding to terpene resins in the same deterrent manner as high-altitude beetles.
3
Apply the Negation Test to the candidate assumption
Negated statement: Lower-elevation beetles ARE significantly more tolerant of terpene resins than high-altitude beetles. If true, the elevated resin levels will fail to deter oviposition, completely undermining the conclusion.
A statement whose logical negation destroys the validity of the conclusion is a required unstated assumption.

Key Concept

Identifying Necessary Assumptions via the Negation Test
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Topics

Identifying Underlying Assumptions

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