ANALYZE THE STIMULUS:

Fact: A newly arrived gecko species, the house gecko, is displacing the previously established mourning gecko in urban areas,
Fact: But populations of the two species are more stable in rural areas far from human settlement.
Fact: The house gecko does not attack the mourning gecko, but in areas where insects congregate it prevents the mourning gecko from feeding on them.

KEY POINT is: competing for food (insect) ==> difference in populations.


ANALYZE EACH ANSWER:

A. In urban areas, geckos are valued because they eat so many insects.
Wrong. Does not explain the difference between populations of the two geckos in urban and rural areas.

B. Geckos defend territories against other members of the same species.
Wrong. Same as A.

C. House geckos that arrive on islands are carried there in boats and planes.
Wrong. Same as A

D. places where there are lighted buildings, insects tend to gather around the light.
Correct. Because the two geckos have same eating habit, they eat insect. In rural areas, because of few lights, the food – “insect populations” is spread, the two geckos seem to have same opportunity to access the food source (Remember fact#3: house gecko does NOT attack mourning gecko). ==> The two geckos' populations seem to be the same in rural areas.
However, in urban areas, insects gather around the light, the the “stronger” gecko will defeat the “weaker” one to get food – insect. That makes the population of house gecko in urban areas is larger the that of mourning gecko.

E. Mourning geckos are all females and reproduce asexually, but house geckos reproduce sexually.
Wrong. Does not help. The main point is “competing for food ==> difference in population”

Hope it helps

I pick D

House gecko prevents mourning gecko from feeding in areas whre insects congregate: Thus if insects tend to congregate near the ligth it is logical to assume that in urban areas mourning gecko has a hard time getting something to eat...

D

I do not have OA, but I selected D

Can someone provide a detailed analysis on this question. Thanks!

FACT 1:The house gecko is displacing the previously established mourning gecko in urban areas
Populations of the two species are more stable in rural areas far from human settlement.

FACT 2:The house gecko prevents the mourning gecko from feeding on insects.

The correct answer will link the two fact, will be something that show a difference between the two areas.

How they reproduce, how they arrived on the island, why they are valued are all out of scope.

A. In urban areas, geckos are valued because they eat so many insects.
C. House geckos that arrive on islands are carried there in boats and planes.
E. Mourning geckos are all females and reproduce asexually, but house geckos reproduce sexually.

The real contenders IMO are B and D.
B. Geckos defend territories against other members of the same species.
This is not actually a difference between the two areas (it is not specified where this happens) and moreover it does not link fact 1 and fact 2.
D. places where there are lighted buildings, insects tend to gather around the light.
where there are lighted buildings (URBAN AREAS) insects tend to gather around the light + FACT 2:The house gecko prevents the mourning gecko from feeding on insects. => FACT 1.

On Pacific islands, a newly arrived gecko species, the house gecko, is displacing the previously established mourning gecko in urban areas, but populations of the two species are more stable in rural areas far from human settlement. The house gecko does not attack the mourning gecko, but in areas where insects congregate it prevents the mourning gecko from feeding on them. Which of the following contributes most to an explanation of the difference between gecko populations in urban and rural areas?

A. In urban areas, geckos are valued because they eat so many insects.
B. Geckos defend territories against other members of the same species.
C. House geckos that arrive on islands are carried there in boats and planes.
D. In places where there are lighted buildings, insects tend to gather around the light.
E. Mourning geckos are all females and reproduce asexually, but house geckos reproduce sexually.


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Answer: Explanation to the difference between gecko population in urban and rural areas.
Need to explain why there is a difference between gecko population in urban and rural areas

Conclusion: house gecko is displacing the previously established morning gecko in urban areas.
Premise: Areas where insects congregate it prevents the mourning gecko from feeding on them.
So if it is proved that this congregation takes place only in urban areas than it gives an explanation or reason for the difference between gecko population in urban areas only
a. wrong. no difference between house and morning gecko.
b. wrong
c. wrong
d. correct: mentioned that two species are more stable in rural areas far from human settlement
rural settlement is the area which is far from human settlement. hence if the congregation of insects take plan in lighted building(urban areas) than it gives an explanation for the given difference. At the lighted building(urban areas) house gecko prevents mourning gecko from feeding on them, which eventually leads to reduced population of mourning gecko.
e. wrong
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On Pacific islands, a newly arrived gecko species, the house gecko, is displacing the previously established mourning gecko in urban areas, but populations of the two species are more stable in rural areas far from human settlement. The house gecko does not attack the mourning gecko, but in areas where insects congregate it prevents the mourning gecko from feeding on them.

Which of the following contributes most to an explanation of the difference between gecko populations in urban and rural areas?

The Congregation of the insects happens in Urban area and doesn't happen the rural areas.

We need to find the reason for that difference

A. In urban areas, geckos are valued because they eat so many insects -> This option doesn't talk about congregation

B. Geckos defend territories against other members of the same species -> Doesn't talk about difference in Urban and rural areas

C. House geckos that arrive on islands are carried there in boats and planes -> Out of scope

D. places where there are lighted buildings, insects tend to gather around the light. -> Provides a reason for the congregation -> Correct

E. Mourning geckos are all females and reproduce asexually, but house geckos reproduce sexually -> We are not talking about reproduction types here
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D
Conclusion - the house gecko, is displacing the previously established mourning gecko in urban areas and not in rural areas.
Premise - The house gecko does not attack the mourning gecko, but in areas where insects congregate it prevents the mourning gecko from feeding on them.
Thus one can pre-think that the conclusion is true because the urban area has more areas where inspects congregate
D specifies one such area
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On Pacific islands, a newly arrived gecko species, the house gecko, is displacing the previously established mourning gecko in urban areas, but populations of the two species are more stable in rural areas far from human settlement. The house gecko does not attack the mourning gecko, but in areas where insects congregate it prevents the mourning gecko from feeding on them.

Which of the following contributes most to an explanation of the difference between gecko populations in urban and rural areas?

A. In urban areas, geckos are valued because they eat so many insects.
Gecko value and the reason for their value is irrelevant.
B. Geckos defend territories against other members of the same species.
This doesn't address urban areas or why one gecko species would have a greater population than the other.
C. House geckos that arrive on islands are carried there in boats and planes.
How the geckos arrive is not relevant.
D. places where there are lighted buildings, insects tend to gather around the light.
The house gecko prevents the mourning gecko from feeding in areas where insects congregate. Insects congregate around light. If the mourning gecko is prevented from feeding this would encourage its displacement.
E. Mourning geckos are all females and reproduce asexually, but house geckos reproduce sexually.
Differing methods of reproduction does not explain the difference in population.

The key is in realizing that urban areas have more lighted buildings than rural areas.

Correct Choice is D) More insects in Urban area under the lights --> House Gecko prevent mourning Gecko feeding on the insects --> Reducing the population of the mourning Gecko

Where does the passage indicate that urban areas have lighted buildings and rural areas don't?

Should the test taker impart his/her outside knowledge to answer this question?

Yes this kind of small leap is acceptable in GMAT. That urban areas have more lighted buildings than rural areas is a basic knowledge that is alright to use.

All other options are irrelevant except D which points that it is in the urban areas that we have lighted buildings--> In places where there are lighted buildings, insects tend to gather around the light --> in areas where insects congregate it prevents the mourning gecko from feeding on them-->hence lower population of mourning gecko in urban areas.

Can we have OA please?


~@p00rv@
Kudos cost nothing...Please be generous

The OA is correct and explanation provided above appears sufficient. If there are any specific questions, please post them here and then click again on the "Request Expert Reply" button.

+1 for D as it speaks about the reason that y are the human geckos replacing the mourning geckos in urban area.

The question asks to identify an option that contributes most to an explanation of the difference between gecko populations in urban and rural areas.

In rural areas ---> no lighted buildings ---> no gathering (congregation) of insects around lights ---> House gecko not stopping Mourning gecko feeding on insects ---> probably no starving of Mourning gecko ---> stable population


In urban areas ---> lighted buildings ---> gathering (congregation) of insects around lights ---> House gecko stopping Mourning gecko feeding on insects ---> probably starving of Mourning gecko ---> reducing Mourning gecko population after introduction of House gecko.

Hence D.
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