Final answer:
A cline is a gradual change in species traits or allele frequencies across a geographical area due to differing ecological conditions, like larger body sizes in cooler climates for warm-blooded animals (latitudinal cline) or different blooming times for flowers along a mountainside (altitudinal cline).
Step-by-step explanation:
Understanding a Cline
A cline is a type of geographic and genetic variation seen in populations of a given species that vary gradually across an ecological gradient. One common example of a cline is observed in warm-blooded animals, such as the tendency of these animals to have larger bodies in cooler climates closer to the Earth’s poles, a phenomenon known as a latitudinal cline. This adaptation allows them to conserve heat more effectively. Another example is how flowering plants may bloom at different times based on their location along an altitudinal cline, which is the change in ecological conditions as the altitude increases on a mountain.
Gene flow between populations on a cline often results in gradual phenotypic changes rather than sudden shifts. Restricted gene flow, however, can lead to more abrupt differences and may even result in speciation. Therefore, a cline represents gradual changes in traits or allele frequencies across a geographic space due to varying ecological conditions.