The phenomenon can be called as an allopatric speciation.
Explanation:
Speciation was coined by Orator F Cook in 1906. Speciation is defined as the evolutionary process by which a group of generalised population undergoes evolution to form one or more species.
Here in the diagram, we can see that the initial population was divided into two groups which were kept at a separation. This is similar to the geographic separation as seen in natural allopatric speciation. Thus they developed into two different species and so, inter breeding isn't favoured between them. Thus it's an allopatric speciation
