Ecologist: Mountain pine beetles have recently expanded into northern boreal forests and begun infesting jack pines, a tree species outside their historic range. Jack pines produce substantially higher levels of monoterpenes—defensive resin chemicals toxic to many bark beetles—than do lodgepole pines, the beetle's traditional host. Nevertheless, researchers observed normal survival rates among beetle larvae developing inside infested jack pines. Therefore, the mountain pine beetle must possess physiological mechanisms that neutralize or tolerate elevated monoterpene concentrations.
Which one of the following is an assumption required by the ecologist's argument?
- AMountain pine beetles prefer colonizing jack pines over lodgepole pines whenever both tree species are present in the same habitat.
- BAny bark beetle species that possesses mechanisms to neutralize monoterpenes will achieve normal larval survival rates in jack pines.
- The beetle larvae developing inside the jack pines were not shielded from the elevated monoterpene concentrations by feeding exclusively on tissues with low chemical levels.Cevap
- DJack pines produce higher concentrations of monoterpenes than every other conifer species native to the northern boreal forest.
- EThe normal survival rate of the larvae proves that monoterpenes are completely ineffective as defensive chemicals against all forest pests.
Cevap
The argument requires assuming that the beetle larvae developing in the jack pines were not shielded from the elevated monoterpene concentrations by feeding exclusively on tissues with low chemical levels.
The correct answer rules out an alternative explanation for the observed survival rate. The ecologist concludes that the beetles must have physiological mechanisms to neutralize or tolerate elevated monoterpenes because they survive in jack pines, which have high levels of those chemicals. This conclusion relies on the assumption that the larvae were in fact exposed to the elevated chemical levels. If the larvae avoided exposure entirely by feeding only on specific low-toxin tissues, their survival would provide no evidence for physiological tolerance mechanisms.
Adım Adım Çözüm
Anahtar Kavram
Necessary Assumption (Defender Archetype)
Alternatif Yöntem
Use the Negation Test: Negate each choice and see which one destroys the conclusion. The statement that larvae avoided exposure by feeding only on low-toxin tissues directly eliminates the need for the inferred physiological mechanisms.
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