Final answer:
The term for the splitting of an existing species range by a new physical barrier is vicariance, leading to allopatric speciation as separated populations evolve independently.
Step-by-step explanation:
The splitting of an existing species range by a new physical barrier is known as vicariance. This is a form of allopatric speciation, which is a process that occurs when populations of the same species become geographically isolated due to a change in the environment. Over time, as the separated populations evolve independently due to different selective pressures, they may become distinct species. An example of such speciation is observed in the case of the northern spotted owl and the Mexican spotted owl, which have become distinct due to potential geographic isolation caused by glaciers during the ice age.