Final answer:
Allopatric speciation occurred in the bellflowers. (option 1)
Step-by-step explanation:
Bellflowers underwent allopatric speciation, a mode of speciation where the emergence of new species is facilitated by geographic isolation. In this case, isolated populations of bellflowers were physically separated by geographical barriers like mountains or bodies of water. This physical separation restricted the gene flow between the populations, leading to reproductive isolation. Over time, as the geographically separated bellflower populations adapted to their specific environments and experienced distinct selective pressures, genetic divergence occurred. Mutations, genetic drift, and natural selection acted independently in these isolated populations, resulting in the accumulation of genetic differences.
The absence of gene flow meant that the bellflower populations evolved along separate trajectories, ultimately giving rise to distinct species. Allopatric speciation is a common mechanism driving biodiversity, emphasizing the role of geographical barriers in shaping the evolutionary trajectory of populations. The bellflowers' journey from a common ancestor to distinct species showcases how environmental factors can act as catalysts for speciation, contributing to the rich tapestry of life's diversity.