Geographic isolation plays a crucial role in allopatric speciation. When populations are separated by physical barriers, they evolve independently, accumulating genetic differences over time. This process can lead to the formation of new species, unable to interbreed if reunited.

Examples like Galápagos finches and Hawaiian Drosophila flies showcase how geographic isolation drives speciation. These cases demonstrate how separated populations adapt to different environments, developing unique traits and reproductive barriers that define distinct species.

Geographic Isolation and Allopatric Speciation

Allopatric speciation process

• Allopatric speciation occurs through geographic separation of populations leads to independent evolution and formation of new species
• Geographic isolation physically separates populations prevents gene flow between groups due to barriers like mountains or bodies of water
• Initial population divides into separate groups evolve independently through genetic drift and natural selection in different environments
• Prolonged separation results in reproductive isolation populations become unable to interbreed if reunited due to genetic incompatibilities

Physical barriers in speciation

• Mountains, rivers, oceans, deserts, and glaciers act as physical barriers prevent movement and interbreeding between populations
• Barriers limit gene flow between separated groups lead to genetic divergence over time
• Small populations experience genetic drift random changes in allele frequencies
• Different environments exert unique selective pressures favor distinct adaptations
• Founder effect occurs in newly established populations limited genetic diversity shapes evolution
• Adaptive radiation results in rapid diversification of species in isolated areas (Galápagos Islands)

Examples of allopatric speciation

• Galápagos finches diversified from South American ancestor into 13 species across islands developed varied beak adaptations for different food sources
• Ensatina salamanders form ring species around California's Central Valley show gradual changes in coloration and genetics
• Hawaiian Drosophila flies evolved over 500 species from common ancestor adapted to various plant hosts
• Cichlid fishes in African Great Lakes (Lake Victoria, Lake Malawi) underwent explosive speciation developed diverse feeding adaptations and colorations

Formation of species over time

• Genetic differences accumulate through mutations, genetic drift, and natural selection in different environments
• Reproductive isolating mechanisms develop prezygotic barriers (mating behaviors) and postzygotic barriers (hybrid inviability)
• Species boundaries reinforced through selection against hybrids when populations come into contact
• Speciation continuum represents gradual process from population divergence to complete reproductive isolation
• Speciation rate influenced by population size, generation time, and strength of selective pressures
• Outcomes include complete speciation with reproductive isolation, incomplete speciation with some gene flow, or fusion of populations if isolation brief