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Explain why scientists believe the Abert’s and Kaibab squirrels are examples of speciation.
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Scientists consider the Abert’s and Kaibab squirrels a classic example of speciation (specifically allopatric speciation) for three main reasons:
1. Geographic isolation
- The Grand Canyon (and associated differences in habitat between the Kaibab Plateau and the opposite rim) physically separated an ancestral squirrel population into two non‑interbreeding populations. That isolation prevented gene flow between the north‑rim and south‑rim groups.
2. Independent evolutionary change
- Once isolated, the two populations accumulated different mutations and were subject to different forces of natural selection, genetic drift and possibly founder effects. Over many generations this produced noticeable differences in morphology and ecology.
3. Observable evidence
- The Kaibab population is distinct in appearance and restricted to the Kaibab Plateau, while other Abert’s squirrels occupy the opposite side and surrounding areas. Genetic studies and comparisons of physical traits show they are differentiated enough to be recognized as separate taxa (often treated as a distinct subspecies or species, depending on the criteria used). The pattern—barrier → isolation → divergence—is exactly what evolutionary theory predicts for allopatric speciation.
Because the Grand Canyon barrier plus the measurable morphological/genetic differences fit the predicted sequence for species formation, scientists view the Abert’s/Kaibab squirrel case as a real-world example of speciation in action.
1. Geographic isolation
- The Grand Canyon (and associated differences in habitat between the Kaibab Plateau and the opposite rim) physically separated an ancestral squirrel population into two non‑interbreeding populations. That isolation prevented gene flow between the north‑rim and south‑rim groups.
2. Independent evolutionary change
- Once isolated, the two populations accumulated different mutations and were subject to different forces of natural selection, genetic drift and possibly founder effects. Over many generations this produced noticeable differences in morphology and ecology.
3. Observable evidence
- The Kaibab population is distinct in appearance and restricted to the Kaibab Plateau, while other Abert’s squirrels occupy the opposite side and surrounding areas. Genetic studies and comparisons of physical traits show they are differentiated enough to be recognized as separate taxa (often treated as a distinct subspecies or species, depending on the criteria used). The pattern—barrier → isolation → divergence—is exactly what evolutionary theory predicts for allopatric speciation.
Because the Grand Canyon barrier plus the measurable morphological/genetic differences fit the predicted sequence for species formation, scientists view the Abert’s/Kaibab squirrel case as a real-world example of speciation in action.
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