Intraspecific variation takes three general forms. Explain each form. How can two populations still be considered part of the same species if great morphological differences exist between the populations due to intraspecific variation?
First, variation among groups within a species can occur because of the variation among local environmental conditions. Such variation is called irregular variation. Second, when the gradual variation of a character of a species can be correlated with a gradual geographic variation, the variation of the character is called a cline. Clines occur because of altitude gradients or latitude gradients, for example. Third, when an abrupt step is plotted in the graph of an otherwise gradually varying clinal character, the two populations on either side of the step are designated as being subspecies, or races. Even with the sometimes great morphological differences between populations due to intraspecific variation, populations are still considered part of the same species if they are not reproductively isolated from each other.
