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”

Answer: D