Which scenario best exemplifies speciation through isolation?

The scenario involving two populations of the same species separated by a mountain range effectively illustrates the concept of speciation through isolation. In this situation, the mountain range acts as a geographic barrier that physically separates the two populations. This isolation restricts gene flow between them, meaning they can no longer interbreed.

Over time, the separated populations may experience different environmental pressures, leading to divergent evolutionary paths. Each population could adapt to their specific environments, accumulating genetic differences that may eventually result in reproductive isolation. This process is fundamental to speciation, as the lack of genetic exchange allows for distinct evolutionary adaptations to arise, ultimately resulting in the formation of new species.

On the other hand, adapting to a new diet, migrating to a new city, or a mutation leading to a color change within a species do not inherently involve isolation mechanisms that would separate gene pools and initiate the speciation process. These scenarios may contribute to variation or adaptation within a population but do not establish the conditions necessary to form new species through isolation.