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Difficulty: HardBridging Conflicting Premises

In a particular forest ecosystem, the primary defense mechanism of the pale-winged Glider Moth against visually hunting predatory birds is its ability to blend in seamlessly with the light-colored bark of the region's dominant birch trees. Three years ago, a rapidly spreading fungal infection caused the bark of almost all these birch trees to turn completely black. Biologists predicted that this stark loss of camouflage would lead to a severe decline in the Glider Moth population due to increased predation. Yet, recent surveys show that the Glider Moth population is now more than double what it was before the fungal infection, even though the number of predatory birds in the forest has not decreased.

Which one of the following, if true, most helps to resolve the apparent discrepancy in the information above?

  1. A
    The visually hunting predatory birds in the forest have highly varied diets and typically shift their hunting efforts to other insect species whenever a specific prey becomes scarce.
  2. B
    While the fungal infection drastically alters the color of the bark, it does not permanently damage the birch trees or reduce the total amount of foliage available for insects to consume.
  3. C
    The darkened tree trunks absorb significantly more sunlight and retain heat longer, causing adult Glider Moths resting on them to expend metabolic energy more rapidly and die sooner than they did on the light-colored bark.
  4. D
    The sudden increase in the Glider Moth population coincided exactly with the period during which the fungal infection was spreading most rapidly across the birch trees.
  5. The fungal infection completely eradicated a species of moss on the birch trunks that previously served as the exclusive breeding ground for a parasitic wasp, a pest that historically destroyed over eighty percent of all Glider Moth eggs.Answer

Answer

The statement explaining that the fungal infection eradicated a parasitic wasp that previously destroyed the vast majority of Glider Moth eggs.
The correct option perfectly resolves the discrepancy by introducing a powerful countervailing force. While the fungal infection harmed the moths by making adult moths visible to birds, it simultaneously eliminated a parasite that was destroying 80% of the moths' eggs. The massive increase in eggs surviving to adulthood more than compensates for the higher rate of adult predation, explaining how the overall population could more than double.

Step-by-Step Solution

1
Identify the opposing premises in the stimulus.
Premise 1: Moths lost their camouflage against predators, so their population should plummet. Premise 2: Predator numbers didn't drop, yet the moth population actually doubled.
Understanding the exact nature of the paradox is required to find the bridging fact.
2
Formulate a structural requirement for the correct answer.
The correct answer must introduce a new, unstated effect of the fungal infection that severely benefits the moths, and this benefit must be powerful enough to completely overshadow the negative impact of being highly visible to predators.
A resolution must allow both premises to be true simultaneously without contradicting either.
3
Evaluate the options against the formulated requirement.
Only the option regarding the parasitic wasp provides a massive reproductive advantage (saving over 80% of eggs) caused by the same fungus that destroyed the camouflage.
This establishes a causal mechanism where the net effect of the fungus on the moth population is overwhelmingly positive, perfectly bridging the conflicting facts.

Key Concept

Bridging Conflicting Premises by identifying an overriding countervailing force.
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Bridging Conflicting Premises

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