Lyme disease is caused by a bacterium transmitted to humans by deer ti

I mean, maybe? Probably? But possibly not? The number of infected ticks could also increase a bit, if somehow the larvae get transmitted from one food source to another.

But the main point here is that it's a strengthen/weaken, not a prove true/false.

If the food is the limiting factor, then "more food = more ticks" but there's no particular reason to expect fewer infected ticks as long as the tick population expands to fill the available food supply -- as many mice as before would presumably be carriers. But if food is not the limiting factor, then diversifying the food choices will presumably lead to some larvae feeding on uninfected food sources instead of white footed mice, so you'd have fewer infected ticks. That's not certainty, but it's plenty good enough to act as the strengthener/weakener that this "useful to evaluate" question needs.
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This is tricky question lads, hope my explanation will help you, at least a little bit.

A - this answer choice seems to be attempting, however, it doesn't help to establish any data from the conclusion, like, if the other species are found in the area only inhabited by white-footed mice - so what? will it really increase the help to decrease the number of infected ticks? who knows? - OUT

B- so B says, how limited the number of other species, if they are not that many that tick has no other choice, but to prey on white-footed mice - looks attempting, let's keep that.

C- it literally says, if we increase the number of other species that prey on white-footed mice, will it influence the number infected ticks, and will lead to the decrease on infections - well looks interesting as well, let's go conservative way, and keep it as well

D- confusing as hell, speaking about larvae ticks and adult ticks, did anybody ask anything about ticks age, sounds very weird - OUT

E- it introduces another premise, trying to say that that might be another species that transmit infectious bacteria to the ticks, rather than mice - it might sound right, but it not, we not talking about other species, we being asked directly about white-footed mice and how the influence deer ticks - OUT of scope

Between B and C, honestly, at first, I personally picked up C, but B is the correct answer. Because if you think about it - if there are other species that prey on white-footed mice, like deer ticks, it means that, you will have less prey for ticks than other animals will become infected, and we start a new COVID-19 like pandemic... joking, but by increasing the number of other species that prey on white-footed mice, we might decrease the population of deer ticks, but it's not what we want to do, we want to decrease the number of Lyme transmitting ticks, thus decrease the number of white-footed and increase the number of other species that ticks prey on.

Hope it helps lads.

There is a lot of confusing answers/explanation on answer choice A, and I would like to offer my two cents here.
A is a tempting choice because when other species is added, the white foot mice population is diluted, hence, lowering tick infection rate. The problem of A is that the negation of A won't help swing the argument to the opposite side.
Other species are not added only to where the white foot mices are. What it shows is that other species are basically everywhere, including where white foot mices are. This negation has the same effect, leading the reader to believe that the argument is still true. If the negation doens't impact the argument in the opposite direction, it makes the answer incorrect.

I want to point out that a lot ppl in this forum claimed that A is out of scope. It is not, don't believe that is the answer you are looking for. Some may argue that deek ticks might have preference on host they feed. This assumption is not stated anywhere in the original question. Even if this is true, you most likely have to apply to all other choices as well, hence, making B funny as well.

GMATIntensive GMATNinja @E-GMAT

Having a hard time understanding this question? Could you please shed some light on Options A B and D?

Thank you.

Can somebody please explain why B is correct? I am still not clear on this.

Check out our earlier analysis of answer choices (A) and (D) here, and our analysis of answer choice (B) here. Let us know whether that clears things up!
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does option B] mean that deer tick population is low in number because whitefooted mice are low in number.

And if we increase more animals on which deer tick feed on, population of deer tick will increase to a larger number

The bold underlined part shouldn't just be white-footed mice—it should be white-footed mice AND other animals on which larval (= baby) deer ticks live.

The deer ticks pick up Lyme disease only from white-footed mice, but they'll happily feed on the mice OR "certain other species". They're indifferent—feeding on the other species is just as good as feeding on the mice. The ticks don't really care, since they don't get Lyme disease; they just carry it and pass it on to humans.




Correct.
And if that happens, then the density of deer ticks on white-footed mice (= the % of mice that host ticks) could stay the same, because the tick population is growing with the availability of additional hosts.

If that's NOT true—i.e., if the tick population is constant—then adding more of the non-mouse species will spread out the population of ticks, so that the % of infected mice goes down. That in turn should decrease the frequency with which humans get infected.

It is stated in the passage that "Generally deer ticks pick up the bacterium while in the larval stage". So, whether the ticks pick up the infection as adults is irrelevant.

Let's understand the argument -
Lyme disease is caused by a bacterium transmitted to humans by deer ticks. - Fact
Generally deer ticks pick up the bacterium while in the larval stage from feeding on infected whitefooted mice. Fact. But "generally" here is important because it seems the GMAT has created an option out of it, and it is a big trap. English meaning of "generally" is "in most cases." It doesn't mean "all." So, maybe 80% of the time, they pick up the bacterium while in the larval stage and 20% in other stages. GMAT doesn't waste a single word, so read every word carefully.
However, certain other species on which the larvae feed do not harbor the bacterium. Contrast and Fact
Therefore, if the population of these other species were increased, the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease—would likely decline. - Conclusion. This is interesting. If we don't understand it well, we are bound to make mistakes.

Let's break the conclusion as it's a cause-effect relationship.
Cause - the population of these other species was increased.
Effect - the number of ticks acquiring the bacterium and hence the number of people contracting Lyme disease—would likely decline. In other words, it means "Few deer ticks acquire the bacterium." (that essentially means less transmission to humans)

So its X causes Y.
What is an assumption in the causal arguments?
One of the assumptions for the causal argument is that there is no other cause. Which means X has to be the cause for Y to happen. In this argument, the Y is not straightforward, and that's the problem.

So, let's understand what Y is and what Y is not.

The effect Y is "Few deer ticks acquire the bacterium." What does it mean? It means if today 100 deer ticks feed on white mice, then with more "other species," say 25 deer ticks will feed on white-footed mice. Right? Yes. Why? Because the number feeding on white-footed mice has to reduce. (NOT INCREASE)
The argument does not say that the deer ticks (DT) population will increase. Against that, the argument is saying "fewer" DT will feed on white-footed mice.

So, what Y is not - If we give more food to DT - and their population explodes - this is not what we want. This is not Y.
What Y is - If we give more food to DT - earlier 100 DT and now 25 DT will feed on white-footed mice. If this happens, only then will the transmission to humans be reduced. Right? Yes. This is what Y is. Are you with me so far? If the answer is Yes, proceed else, read again. Otherwise, it'll confuse you.

Okay, if you are good now, let's move to the next step
So, if we translate the assumption into our argument's language, we will assume that "the population of deer ticks does not depend on the population of other species." Ok? Let's fill our assumption into the argument and see.

More other species (X) - the population of deer ticks does not depend on the population of other species (assumption) - Few deer ticks acquire the bacterium (Y).

Let me explain one last time before we proceed.
If the DT population depends on the population of other species, then the moment we increase the food supply, the DT population will explode. And if the population explodes, the spread to humans may increase or stay the same but not decline.
But if the DT population doesn't depend on the population of other species, then the moment we increase the food supply, out of the same 100 DTs, more, say 75, will feed on other species (uninfected) and 25 on white-footed mice (infected) - It'll in turn reduce the spread to humans.

If you have understood and survived so far, congratulations! Let's move to the next step.

How do we create evaluation questions? We create evaluation questions along the lines of assumptions. That's why you may have heard some experts saying try Yes and no. So, it's the same as adding the assumption (will strengthen) and removing the assumption (weaken) the conclusion.

So, based on our assumption that "the population of deer ticks does not depend on the population of other species," what will be the evaluation question we ask? We ask, "Does the population of deer ticks limited (depends on those limited resources for survival or growth) by the population of other species?"
If the answer is Yes, that means the moment we offer more resources (we remove the limitation), the population will explode, and we'll not achieve our goal.
If we say No, that means the moment we offer more resources (we remove the limitation), more of the existing DTs will feed on the other resources (uninfected), and as fewer DTs feed on the infected white-footed mice, less transmission to humans.

Option elimination will be a cakewalk if you have survived so far. Let's do it.

A. Whether populations of the other species on which deer tick larvae feed are found only in areas also inhabited by white-footed mice. - it does not matter. This is not in line with our assumption. But if it doesn't give peace to you. Let's do Yes/No to check
Yes, other species are only found in the areas inhabited by white-footed mice. Then may we need only to add more "other species" here as these are problem-maker areas and not other areas.
No, other species are not just found in the areas inhabited by white-footed mice - then we may need to spread the "other species" over a wider area.

This is not our assumption that we can create an evaluate question, but it can certainly answer where to introduce other species." Location is not our scope. So it is out of scope.

B. Whether the size of the deer tick population is currently limited by the availability of animals for ticks' larval stage to feed on - ok.

C. Whether the infected deer tick population could be controlled by increasing the number of animals that prey on white-footed mice. - Alternate plan. Moreover, Our problem is not the DT population. Our problem is that there are more DTs that feed on white-infected mice. This is a great distortion if we don't read properly.

D. Whether deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have fed. - Remember "generally" we discussed above. So, from the argument, we already know that there can be other stages (and not just the larval stage) for the DT to get infected. This option does not tell us anything new if we are reading correctly. But if we don't read properly, this is a perfect trap.

E. Whether the other species on which deer tick larvae feed harbor any other bacteria that ticks transmit to humans. It's out of scope, please. We have enough to deal with from what is within the scope of the argument.