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Difficulty: MediumStrengthening Arguments

Ecologists observed that in coastal pine forests where native beetle populations recently declined, a species of parasitic fungus began infecting over 40 percent of mature pine trees. The ecologists hypothesized that the beetle larvae, which burrow into pine bark, deposit a chemical secretion that inhibits fungal spore germination, thereby protecting the trees from infection.

Which of the following findings, if true, would provide support for the ecologists' hypothesis? Select all that apply.

  1. Laboratory tests confirm that synthetic versions of the chemical secretion produced by beetle larvae inhibit fungal spore germination at concentrations typical in pine bark.Answer
  2. In nearby coastal pine forests where beetle larvae populations remained stable, fungal infection rates among mature pine trees were significantly lower than 40 percent.Answer
  3. C
    Fungal infection rates in mature pine trees began to rise sharply several years before the decline in native beetle populations was recorded.
  4. D
    Other tree species in the same coastal pine forests that are not host to beetle larvae also experienced a marked increase in fungal infection rates during the same period.
  5. E
    Mature pine trees infected with the fungus generally display a marked reduction in overall resin production within six months of initial exposure.

Answer

The argument is strengthened by demonstrating that the larval secretion actively inhibits fungal germination in controlled laboratory conditions and by showing that forests retaining stable beetle populations maintained lower fungal infection rates.
The argument proposes a causal mechanism: beetle larvae protect trees from fungal infection via an inhibitory chemical secretion. The statement verifying that the larval secretion chemically inhibits fungal germination in lab tests directly confirms the plausibility of this mechanism. Additionally, the statement observing lower infection rates in forests with stable beetle populations provides control data showing that beetle presence correlates with protection from the fungus.

Step-by-Step Solution

1
Identify the core conclusion and proposed mechanism
Conclusion/Hypothesis: Beetle larvae protect pine trees because their chemical secretion inhibits fungal spore germination.
Strengthening questions require finding statements that increase the likelihood that this specific mechanism is correct.
2
Evaluate empirical verification of the causal agent
The finding confirming that synthetic larval secretion inhibits fungal spore germination at typical bark concentrations provides direct experimental support for the proposed biological mechanism.
Validating that the biological agent possesses the requisite chemical property confirms a critical underlying assumption.
3
Evaluate comparative control evidence
The finding that forests with stable beetle populations maintained significantly lower infection rates serves as comparative control data.
Showing that the effect (low fungal infection) persists where the cause (beetle larvae) remains active reinforces the causal connection.

Key Concept

Strengthening Arguments via Mechanism Validation and Comparative Controls
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Topics

Strengthening Arguments

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