Astragalus linifolius, a rare plant species that is found only in the Colorado region of the United States, reproduces when a pollinating agent like a fly or a bee carries the pollen grain from the male part of one plant to the female part of another plant of the same species. To maintain the population of this species, the use of pesticides that control grasshoppers should be banned in this region. These pesticides also often result in significant mortality among the Bombylius flies that are the most important pollinating agents of A. linifolius.

Which one of the following, if true, most strengthens the argument?

Question

TheoryPractice · Accepted Answer

Bombylius flies do not reproduce very fast and their populations do not recover for many years after one spraying of a pesticide that controls grasshoppers.. Solution

Argument construction

The argument starts with a premise – Premise 1:

Astragalus linifolius (context-setting information: this is a rare plant species that is found only in the Colorado region of the United States) reproduces when a pollinating agent like a bee or a fly carries the pollen grain from the male part of a plant and deposits it onto the female part of another plant of the same species.

From this premise, it becomes clear that pollinating agents like bees and flies are necessary for the reproduction of A. linifolius to take place.

Next comes the conclusion of the argument:

To maintain the population of Astragalus linifolius (a rare legume species that is found only in the Colorado region of the United States), the use of pesticides that control grasshoppers should be banned in this region.

This conclusion is followed by two more premises:

Premise 2 - These pesticides result in significant mortality among the Bombylius flies.
Premise 3 - Bombylius flies are the most important pollinating agents of A. linifolius.

Here is how these premises are used to draw the conclusion:

From Premise 1, we know that A. linifolius cannot reproduce without pollinating agents. From Premise 3, we know that Bombylius flies are the most important pollinating agents of A. linifolius. By combining Premises 1 and 3, we can draw a subsidiary conclusion that to conserve A. linifolius, it's probably important to conserve Bombylius flies too. A decline in the numbers of the latter is likely to result in a decline in the numbers of the former.

When this subsidiary conclusion is combined with Premise 2, we draw the conclusion that to maintain the population of A. linifolius, the use of pesticides that control grasshoppers should be banned in that region.

We are looking for the answer choice that provides additional information which makes this conclusion stronger than when the above two premises are used alone.

Let us analyze the options one by one.

Answer choices explanation

This option is incorrect. This argument is concerned with the maintenance of population of a particular species. The population of a species would be maintained if its death rate and birth rate remain in equilibrium. The life-span of a species is irrelevant to the maintenance of its population and, therefore, to this argument.
This option is incorrect. If there are other pollinating agents through which A. linifolius can reproduce, then, assuming that these pollinating agents are not impacted by pesticides that control grasshoppers, this plant species might survive even if these pesticides are not banned. Therefore, this statement actually weakens the conclusion.
This option is incorrect. There may be pesticides that are more toxic to the Bombylius flies than the pesticides mentioned in the argument, but this does not strengthen the argument that to save A. linifolius, the pesticides that control grasshoppers should be banned. For example, consider the statement 'to get better health, you should eat less sugar.' This statement is of the same format as the conclusion drawn in this argument: To achieve Goal A, do Action X. Does a statement that eating oily foods is even worse for your health than eating sugar strengthen the above example statement? It does not.
This option is correct. Suppose that Bombylius flies had been able to reproduce fast. Then, even if one spraying had significantly reduced the number of flies in a region from, say, 1000 to a mere 100, their fast breeding would have restored the population number to its pre-spraying level pretty soon and so there would probably not have been much adverse impact on the amount of pollination that these flies did for A. linifolius and, therefore, in the population of this plant species. However, this statement tells us that the populations of Bombylius flies do not recover for many years post a pesticide spraying. In those years, therefore, the extent of reproduction of A. linifolius is likely to decline, which in turn, is likely to decrease the population of this plant species.
This option is incorrect. That other plant species have suffered greater declines than A. linifolius since the spraying of pesticides that control grasshoppers started is irrelevant to the conclusion drawn for how the population of A. linifolius may be maintained.

Related questions

Free practice here. Timed mocks when you are ready.