Ferrets are unable to withstand long periods of cold weather and must hibernate throughout much of the winter. Hibernating sites are in short supply, and ferrets only survive if they can find holes in trees that fit their body size. Very small tree holes are in short supply because they are generally colonized by stinging wasps that chase away ferrets. Very large tree holes are in short supply because they are colonized by snakes that eat ferrets. The limited supply of tree holes should result in:
A. balancing selection on ferret body size
B. directional selection on ferret body size
C. disruptive selection on ferret body size
D. sexual selection on ferret body size
E. stabilizing selection on ferret body size

Stabilizing selection is a type of natural selection at which medium or mean features of a trait are favored above extreme trait values. In this example, ferrets must look for hibernating sites that are not very small because they often are colonized by stinging wasps; and that are not very large because they often are colonized by snakes. Therefore, ferrets that have a medium or mean body size are favored, which is an example of stabilizing selection.