In a population of parrots on an island, there is considerable variation in beak size. Parrots with small, thick beaks can efficiently eat locusts insect), while birds with long, thin beaks can efficiently eat beetles. Both food types are available on the island. Which of the following types of selection, and effects on phenotypic variation would you expect to see?
A) Directional selection; phenotypic variation increases.
B) Directional selection; phenotypic variation decreases.
C) Disruptive selection; phenotypic variation is maintained.
D) Disruptive selection; phenotypic variation decreases.
E) Directional selection; phenotypic variation remains the same.

Question

Quizplus · Accepted Answer

Disruptive selection is favored when contrasting phenotypes are better adapted to different environmental conditions. In this case, parrots with small, thick beaks are better adapted to eating locusts, while birds with long, thin beaks are better adapted to eating beetles. This maintains phenotypic variation in the population since both traits are fit for survival and reproduction. The other choices are not applicable in this scenario; directional selection would favor one extreme phenotype and decrease variation, while there is no reason to expect no change in phenotypic variation.

In a Population of Parrots on an Island, There Is