Suppose an entire colony of lemmings is chased by a predator and most of them jump off a cliff and perish. Fortunately, a few of them don't jump and re-establish their colony (Re-established Colony) and a few of the jumpers land in the water, survive the fall and establish a second colony on a nearby island (Island Colony). Which of the following characterizes the type of change causing a reduction in the genetic variation that occurs in these 2 colonies?