Question

question 4 of 25
three islands have three different habitats. island x has little ground
vegetation and a lot of trees. island y has a lot of ground vegetation but fewer
trees. island z has a lot of ground vegetation and many trees. the same
species of tortoise lives on all three islands and eats plants. the tortoises
cannot travel between the islands. over time, the population of tortoises on
island x develops a longer neck than the populations on the other islands.
which two factors likely contributed to the changes caused by natural
selection in this tortoise population?
a. the tortoises on island x reproduced much more quickly than the
tortoises on the other islands.
b. the tortoises on island x had more food than they needed, so
there was no competition.
c. the tortoises had a range of neck length phenotypes that could
be inherited.
d. having a longer neck gave some tortoises an advantage when
competing for food.

Explanation:

Natural selection requires variation (phenotypes that can be inherited) and differential survival/reproduction (advantage in competition). Option C provides the genetic variation (inherited neck - length phenotypes), and option D gives the selective advantage (longer - necked tortoises better at getting food in Island X's habitat with more trees). Option A about reproduction speed is not related to the neck - length change mechanism. Option B is incorrect because if there was no competition, natural selection (which acts on competition for resources) would not drive the neck - length change.

Answer:

C. The tortoises had a range of neck length phenotypes that could be inherited.
D. Having a longer neck gave some tortoises an advantage when competing for food.