The fish in a certain population average 10 millimeters in length. Imagine that a population of predatory birds arrives in the area, but they cannot eat fish longer than 15 millimeters. After a decade, if the fish average 14 millimeters in length, what probably happened?
A) The presence of the predator caused mutations for larger fish to occur.
B) The longer fish survived and produced more offspring than shorter fish.
C) There was stabilizing selection for fish length.
D) The fish and the predator coevolved.
E) There was disruptive selection for fish length.

Question

Quizplus · Accepted Answer

The presence of predatory birds that cannot eat fish longer than 15 millimeters would naturally select for fish that are closer to this size limit, as they would be less likely to be preyed upon. Over time, this selective pressure would result in an increase in the average size of the fish population, as the longer fish would have a survival advantage and thus produce more offspring. This is an example of directional selection, where one extreme of a trait (in this case, larger size) becomes more common in the population.

The Fish in a Certain Population Average 10 Millimeters in Length