Four out the five living tiger subspecies' morphology (physical structure and appearance) exhibit a cline. A cline occurs when a single species gradually begins to look different over its geographic distribution as it adapts to varying climates and habitats. Therefore the species at the northern end of their geographic distribution may look very different in size, color, hair-density, etc. than their southern counterparts. The Tiger cline depicts subspecies decrease in size and have darker stripe coloration the further south their range extends.