Rabbits were introduced to Numa Island in the nineteenth

Premise -
1) Overgrazing causes damage to agriculture
2) government plan to introduce virus - this virus helps in eradicating rabbit population but chances are also there that it will infect bilby

Conclusion -
1) Plan will have positive effect on agriculture
2) Plan will have negative effect on native wildlife.

Approach -
We need to find an option which will show that
1) either plan will have negative effect on agriculture
2) or plan will have positive effect on agriculture.
OR BOTH.

Hope this helps.

I don't think option C states that the plan will have a positive effect, I think the rabbits are already having a negative effect on the native marsupial, and hence gives us a reason that the virus will not have worsen this situation further.

By Positive effect I dont mean literally positive effect.
When you are solving CR question. You need to find logic which suits best for you and how you can deduce the same.
For me positive effect was nothing but ( any effect that shows no negative effect on bilbies).
As in C, it is stated that since rabbit are taking away the plant on which bilbies feed, so by killing rabbit bilbies are getting their food back.
So it is in a way showing reverse of negative effect on bilbies.

Thanks

The hint lies in the last sentence.

"The government’s plan, therefore, may serve the interests of agriculture but will clearly increase the threat to native wildlife"
Agriculture is given the priority over the threat to native wildlife.

Choice C - Best pick

Kill rabbits with virus - bad for bilbies - threat to native wildlife

A. Wildlife not domestic animals... Out of scope!
B. strengthener...
C. Virus means more food for bilbies... Weakener
D. How bout bilbies? Does nothing to weaken
E. doesn't tackle the issue of whether it is really or not really a threat

Answer: C

C
Conclusion - The government’s plan, therefore, may serve the interests of agriculture but will clearly increase the threat to native wildlife
Premises - Use of virus; chance of virus affecting the bilby
Weaken - That govt plan would not increase the threat to bilby

C states that rabbits are eating away bilby food source and thus eliminating rabbits can increase bilby population - this is best choice

Responding to a pm:

Between (A) and (C):
Premises:
- Rabbits are a menace to agriculture.
- The government proposes to use a virus to control their population.
- However, the virus could infect the bilby.

Conclusion: The plan may serve the interests of agriculture but will clearly increase the threat to native wildlife.

Notice here that the author says 'may serve the interests' so he is not very particular about the plan serving the interests of agriculture. But he says that it will 'clearly increase the threat to wildlife'. If we want to weaken the conclusion, we should try to weaken 'will clearly increase the threat to wildlife'.
We need to prove that the plan 'may not increase' the threat to wildlife.

A. There is less chance that the virus will infect domestic animals on Numa than that it will infect bilbies.

The conclusion clearly says "...increase the threat to native wildlife".
The author is worried about the threat to wildlife. (A) tells us that the virus will be less of a threat to domestic animals. The author is not worried about domestic animals at all. His concern is only wildlife. (A) doesn't weaken his conclusion that the plan will not threaten WILDLIFE.

C. Overgrazing by rabbits endangers many of the plants on which bilbies feed.

(C) says that rabbits are endangering bilbies (by reducing their food). The plan will reduce the rabbit population which will be good for the bilbies. It might infect bilbies too which will be bad for the bilbies. We don't know what the overall effect will be. Hence, we can say that the plan 'may not increase the threat or it may'. We have cast a shade of doubt on the conclusion which was 'the plan will clearly increase the threat to wildlife'. This is what we set out to do.

Answer (C)

Premise -
1) Overgrazing causes damage to agriculture
2) government plan to introduce virus - this virus helps in eradicating rabbit population but chances are also there that it will infect bilby

Conclusion -
1) The plan will have a positive effect on agriculture
2) The plan will have a negative effect on native wildlife.

Approach -
We need to find an option which will show that
1) either plan will have a negative effect on agriculture
2) or plan will have a positive effect on agriculture.
OR BOTH.

Hope this helps.

The argument is that the government's plan may serve the interests of agriculture but it will INCREASE the threat to native wildlife.
This plan is to introduce a virus that kills out rabbits but also threatens (to an unknown degree) the population of the bilby.

[This actually happened in Australia - the virus is called the myxomatosis virus and it's quite horrible what it does to rabbits - Cats are a more concerning threat now!]

What weakens this argument?
A the argument isn't concerned with domesticated animals. It's concerned with the bilby. Incorrect.
B this doesn't weaken the plan. This strengthens the cause for some external influence actually.
C this tells us that rabbits are taking away the food source of the bilby and are endangering the bilby. Endangering is a pretty heavy term. The plan only increases the threat to the bilby, it doesn't endanger them. So this could clearly presents a greater threat to the Bilby. As such, this weakens the argument.
D is incorrect - what is true of others may not be relevant or true of our plan.
E is incorrect - if anything this suggests that we should go full steam ahead with the plan, so it doesn't weaken the argument at all.

Conclusion: The government’s plan, therefore, may serve the interests of agriculture but will clearly increase the threat to native wildlife.

bilby, an endangered native marsupial == animal
native wildlife.== animal

B. There are no species of animals on the island that prey on the rabbits. (B. There are no species of animals ( wildlife or bilbies) on the island that prey on the rabbits( killed due to virus).)
There are no animals on island no animal (including marsupial and wild animal) would feed on rabbits that were killed by virus. Hence no danger of spreading virus to any animal (including native wildlife)
So clearly weaken the threat to native wildlife

C. Overgrazing by rabbits endangers many of the plants on which bilbies feed.
>> the discussion started: Overgrazing by the enormous population of rabbits now menaces the island’s agriculture. Because rabbits maybe eating lot of these plants anyways.
Moreoever conclusion is about threat to native wildlife. But this options talks about bilbies.


Please help to reach at correct answer considering above lines of thoughts.

VeritasKarishma

When the argument says "native wildlife", it is referring to "native bilbies".

(B) No animals prey on the rabbits means other animals will not be affected by what happens to rabbits. (Native bilby may get the virus if it is introduced in rabbits. they don't need to prey on rabbits to get the virus. If you introduce a virus in the ecosystem, it will spread. Other animals may not catch it because their DNA is different but bilby may hence bilby gets endangered)

This option does not weaken the idea that bilby may get affected by virus too and hence introducing the virus puts it in danger. Hence it doesn't weaken our stand that the virus is a threat to native wildlife (bilby)

(C) Rabbits are endangering bilbies by eating their food. Introducing the virus will reduce rabbit population so bilbies will have more food available. Hence introducing virus works in favour of bilbies. Of course, bilbies still could catch the virus which would work against them. So we don't now overall what the virus will do to bilby population. So we have introduced a question mark on 'virus is clearly a threat to native wildlife (bilby)' That is all we needed to do - weaken the conclusion.

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