Final answer:
Geographic separation between populations can lead to differences in phenotypic variation across an ecological gradient, such as latitudinal and altitudinal clines.
Step-by-step explanation:
Geographic separation between populations can lead to differences in the phenotypic variation between those populations. One type of geographic variation, called a cline, can be seen as populations of a given species vary gradually across an ecological gradient. Species of warm-blooded animals, for example, tend to have larger bodies in the cooler climates closer to the earth's poles, allowing them to better conserve heat. This is considered a latitudinal cline. Alternatively, flowering plants tend to bloom at different times depending on where they are along the slope of a mountain, known as an altitudinal cline.