What type of speciation occurs when groups of organisms are separated by a geographic barrier?

When groups of organisms are separated by a geographic barrier, the type of speciation that occurs is allopatric speciation. This process involves physical geographic separation, such as mountains, rivers, or distances, preventing gene flow between populations. Over time, these isolated populations may undergo evolutionary changes due to different selective pressures, genetic drift, or mutations, leading to the development of distinct species.

In this scenario, the physical barrier is crucial because it allows populations to evolve independently. Each group adapts to its unique environment, which can result in divergent evolutionary paths. Such barriers can be as minor as a small distance that affects migration or as significant as large scale geological features that drastically alter habitats. This geographic separation is a key factor that distinguishes allopatric speciation from other forms, like sympatric speciation, which occurs without physical barriers, or parapatric speciation, which involves adjacent populations with some gene flow.

By understanding the mechanisms of allopatric speciation, one can appreciate how the geographic context of populations contributes to biodiversity and the evolutionary processes that shape the species we observe today.