Final answer:
Stabilizing selection reduces variance without changing the average trait value by favoring the average phenotype and selecting against the extremes, reducing genetic variance and maintaining the mean fur color in a population of forest-dwelling mice.
Step-by-step explanation:
The selection that reduces variance without changing the mean value of a trait is known as stabilizing selection. This type of natural selection favors the average phenotype by selecting against the extremes. Taking the example of a population of mice living in the woods, stabilizing selection would favor those whose fur color closely matches the consistent shade of brown of the forest floor. Mice with fur colors that are significantly lighter or darker stand out and are more likely to be predated, thus their alleles become less frequent in the gene pool. As a result, the population's genetic variance decreases while the mean fur color remains consistent.