Final answer:
A cline is a type of geographic variation seen in populations of a given species that vary gradually across an ecological gradient. Examples include warm-blooded animals having larger bodies in cooler climates closer to the poles and flowering plants blooming at different times along a mountain slope.
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.