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Zorluk: OrtaNecessary Assumption

Ecologist: Over the past five years, the population of the western bog fritillary butterfly in the Merrow Valley wetlands has declined by 40 percent. During this same period, agricultural drainage projects in adjacent uplands substantially lowered the local water table, which in turn reduced the abundance of marsh violet, the fritillary caterpillar's sole larval food source. Although adult fritillaries can disperse several kilometers across open terrain, the hypothesis that the population simply relocated to nearby unmonitored wetlands is incorrect; the decline in the Merrow Valley represents an actual net loss of fritillary individuals rather than a migration.

Which of the following are assumptions on which the ecologist's argument depends? (Select all that apply.)

  1. The fritillaries that disappeared from the Merrow Valley did not successfully establish or augment breeding populations in unmonitored wetlands in the region.Cevap
  2. B
    Adult western bog fritillaries are completely incapable of laying viable eggs on any wetland plant species other than the marsh violet.
  3. The observed 40 percent drop in the Merrow Valley fritillary population was not matched by an equivalent increase in the fritillary population across nearby unmonitored wetlands.Cevap
  4. D
    If agricultural drainage projects in the uplands were halted, the Merrow Valley fritillary population would recover to its previous levels within five years.
  5. E
    Agricultural drainage in the uplands caused no other environmental changes in the Merrow Valley wetlands besides the reduction in marsh violet abundance.

Cevap

The argument depends on the assumptions that the displaced butterflies did not successfully establish or augment breeding populations in unmonitored wetlands, and that the decline in the surveyed valley was not matched by an equivalent population increase in those unmonitored wetlands.
The conclusion explicitly denies the relocation hypothesis, asserting that the local decline represents a net loss of individuals. For this reasoning to hold, it is strictly necessary that the butterflies did not simply move to unmonitored areas and thrive there. Both the option stating that the butterflies did not successfully establish or augment breeding populations in unmonitored wetlands and the option stating that the drop was not matched by an equivalent increase elsewhere are required; negating either statement directly proves that relocation occurred, fatally undermining the ecologist's conclusion.

Adım Adım Çözüm

1
Analyze the argument's structure and identify premises and conclusion.
Premise 1: Merrow Valley fritillary population declined by 40% over 5 years. Premise 2: Drainage lowered the water table, reducing marsh violet (sole larval food source). Counter-premise noted: Adult butterflies can disperse several kilometers. Conclusion: The decline represents a true net loss of individuals, not a relocation/migration to unmonitored wetlands.
Isolating the gap between the observed local decline and the claim of overall net loss is essential to determining what must be assumed.
2
Formulate the essential logical bridge (Supporter/Defender role).
To conclude that the decline is an actual net loss rather than a migration, the author must rule out the possibility that the missing butterflies successfully relocated, survived, and reproduced in unmonitored areas.
A necessary assumption must protect the conclusion from the unmonitored relocation counter-hypothesis.
3
Apply the Negation Test to each option.
Negating the statement about butterflies establishing breeding populations in unmonitored wetlands proves the relocation hypothesis true, destroying the author's claim. Negating the statement about the lack of an equivalent numerical increase in unmonitored wetlands shows total numbers remained constant, also destroying the conclusion. Negating the remaining statements leaves the core conclusion intact.
A required unstated assumption, when negated, must completely invalidate the author's conclusion.

Anahtar Kavram

Necessary Assumption (Defender Assumption and Negation Technique)
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Konular

Necessary Assumption

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