In Colorado subalpine meadows, nonnative dandelions co-occur with a native ﬂower, the larkspur. Bumblebees visit both species, creating the potential for interactions between the two species with respect to pollination. In a recent study, researchers selected 16 plots containing both species; all dandelions were removed from eight plots; the remaining eight control plots were left undisturbed. The control plots yielded significantly more larkspur seeds than the dandelion-free plots, leading the researchers to conclude that the presence of dandelions facilitates pollination (and hence seed production) in the native species by attracting more pollinators to the mixed plots.
Which of the following, if true, most seriously undermines the researchers’ reasoning?
(This question is from Official Guide. Therefore, because of copyrights, the complete question cannot be copied here. The question can be accessed at GMAT Club)
Understand the Passage
In Colorado subalpine meadows, nonnative dandelions co-occur with a native ﬂower, the larkspur.
In a certain region, some non-native flower occurs with a native flower.
(This is what I understand as I read this sentence. There are a lot of unfamiliar words in this sentence. If I try to remember everything, I will take a lot of time. To minimize time, I just keep the gist in the mind and will refer to this sentence again as these terms are used again in later sentences. If these details are not used later in the argument, I have saved myself from bothering about these details.)
Bumblebees visit both species, creating the potential for interactions between the two species with respect to pollination.
Bumblebees visit both species (both native and non-native flowers) and thus create a possibility of interaction between the two species w.r.t pollination.
In a recent study, researchers selected 16 plots containing both species; all dandelions were removed from eight plots; the remaining eight control plots were left undisturbed.
A study was done. A total of 16 plots were observed. Dandelions (since it is referred again and in an important way, I’ll go back to the first sentence to see what dandelions are. They are non-native species) were removed from 8 plots and the remaining 8 plots had both dandelions and larkspur (native flower).
The control plots yielded significantly more larkspur seeds than the dandelion-free plots, leading the researchers to conclude that the presence of dandelions facilitates pollination (and hence seed production) in the native species by attracting more pollinators to the mixed plots.
(As I read this sentence, I recognize that control plots refer to one of the two groups of 8 plots. I go back to the previous sentence to figure what control plots refer to. Control plots are the plots in which both dandelions and larkspur exist.) The control plots yielded significantly more larkspur seeds than the other 8 plots (from which dandelions had been removed). Based on this observation, researchers concluded that dandelions help larkspur flowers by attracting more pollinators. More pollinators lead to greater pollination and thus greater seed production.
Predict an Answer
The given argument is a causal argument. We are assuming causality based on the given correlation. We know that the plots containing both species have yielded more seeds of larkspur than the plots containing just larkspur. However, it is our assumption that the presence of dandelions has helped in the greater seed production. Probably, the plots containing both species were more productive to begin with. In such a case, the researchers’ conclusion will fall apart. Also, any statement that indicates an alternate cause for the difference in levels of seed production will be weakener.
(A) Incorrect. The option implies that in a mixed plot, bumblebees will spend a greater proportion of time on dandelions than on larkspurs. However, even in this case, it is entirely possible that dandelions attract so many bumblebees that even though bumblebees spend a smaller proportion of time on larkspurs, these larkspurs are still at an advantage over larkspurs in fields without dandelions. Given our observation (in the argument) regarding the difference in the seed production, this case seems likely. Thus, the conclusion holds as is in the presence of this option since the reasoning of the argument stands as is.
(B) Incorrect. This option rather strengthens the argument by saying that increased number of pollinators can lead to higher seed production. If the option had suggested that pollinators cannot augment seed production, it would have weakened the argument since in such a case, we wouldn’t be able to say that the presence of dandelions leads to higher seed production by attracting more pollinators. More pollinators wouldn’t increase seed production in such a case.
(C) Incorrect. The conclusion is that the presence of dandelions helps native species. Even if uncontrolled production of dandelions can harm native species, the conclusion that dandelions can help native species still holds. For example: If I say that intaking iron is good for health, saying that excess amount of iron can harm does not weaken my statement. The statements that intaking iron is good for health and that excess amount of iron is bad for health can coexist peacefully at the same time.
(D) Incorrect. The argument is not concerned with species’ fitness. Therefore, what is a more reliable measure of species’ fitness is irrelevant to the argument.
(E) Correct. This is a tricky option. One can mark this option only if one pays attention to the details in this statement ‘all dandelions were removed from eight plots; the remaining eight control plots were left undisturbed’. This statement means that the plots containing only larkspur were ‘disturbed’ and the plots containing both the species were ‘undisturbed’. This option exploits this difference in the two groups of plots to present an alternate cause for the difference in seed production. This option suggests that the reason for the lower seed production in the dandelion-free plots is ‘soil disturbances’, and thus the reason for the higher seed production in control group (which had both species of plants) is ‘the absence of soil disturbances’ and not the ‘presence of dandelions’.
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