The ears, feet and tail of north american mammals are often smaller in northern species than they are in southern species. explain the adaptive advantage of these size differences

This phenomenon can be explained by Allen's rule. It says that the body proportions and shape may vary in different climates. The temperature decreases as the latitude increases, so in the northern region is much colder. Animals must preserve heat in such conditions. So, exposed surface areas of the body, such as the ears, feet, and tail, are usually minimized to minimize heat loss in the cold climate. Therefore, northern species often have smaller ears, feet, and tail than the southern species. 

From a high concentration to a low concentration.