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Zorluk: OrtaNecessary Assumption

Marine Ecologist: Over the past decade, kelp forest canopies off the northern Pacific coast have declined by over 60 percent, coinciding with a dramatic population boom of herbivorous purple sea urchins. Laboratory assays demonstrate that purple sea urchins consume giant kelp holdfasts at three times the rate of other native benthic grazers. Therefore, the widespread loss of northern Pacific kelp forests was caused primarily by the direct grazing pressure exerted by the surging purple sea urchin population rather than by recent shifts in ocean temperatures.

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

  1. Recent shifts in ocean temperatures were not themselves sufficient to cause widespread kelp mortality independently of sea urchin grazing.Cevap
  2. The feeding behavior of purple sea urchins observed in laboratory assays reflects their capacity to consume kelp holdfasts in natural marine habitats.Cevap
  3. C
    Purple sea urchins are the only herbivorous species in the northern Pacific ecosystem that feed on giant kelp holdfasts.
  4. D
    Reducing the purple sea urchin population to its historical baseline will fully restore the kelp forest canopy to its prior density.
  5. E
    Kelp forest canopies off the northern Pacific coast experienced no significant population fluctuations prior to the past decade.

Cevap

The argument depends on the assumptions that shifts in ocean temperatures were not independently sufficient to cause the mortality, and that laboratory feeding behaviors reflect wild feeding capacities.
Both correct statements represent indispensable logical requirements of the argument. The statement addressing ocean temperatures defends the argument against an explicitly dismissed alternative cause, because if temperature shifts alone caused the mortality, urchin grazing could not be the primary cause. The statement connecting laboratory assays to wild environments serves as an essential supporter assumption, ensuring that the empirical evidence gathered in captivity actually applies to the natural ecosystem being evaluated.

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1
Isolate the conclusion and supporting premises of the argument.
Premises: Kelp canopy declined 60% alongside an urchin population surge, and lab assays show urchins consume kelp holdfasts rapidly. Conclusion: The decline was caused primarily by urchin grazing pressure rather than shifts in ocean temperatures.
Identifying the exact scope of the conclusion determines which unstated gaps must be closed.
2
Apply the Negation Test to potential defender assumptions regarding alternative causes.
Negating the statement about ocean temperatures reveals that if temperature shifts alone caused the widespread mortality, the conclusion that urchins were the primary cause falls apart.
A necessary assumption must fatally undermine the conclusion when logically negated.
3
Apply the Negation Test to potential supporter assumptions linking laboratory evidence to natural conditions.
Negating the statement about laboratory observations reveals that if lab feeding rates do not reflect real-world capacity, the premise fails to establish that wild urchins caused the 60% canopy loss.
Extrapolating from controlled experimental settings to complex natural ecosystems requires that the experimental results hold true in nature.

Anahtar Kavram

Identifying required unstated premises using the Negation Test and eliminating extreme or out-of-scope distractors.
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Konular

Necessary Assumption

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