What Is Parapatric Speciation?

Parapatric speciation occurs when populations of a single species occupy adjacent but non-overlapping geographic areas. These populations are not completely isolated by physical barriers, as in allopatric speciation, but they are separated by differences in their habitats. Gene flow between the populations is possible but limited, often due to environmental gradients or selective pressures that vary across the landscape.

Key Features of Parapatric Speciation

• Contiguous Distribution: Populations are next to each other geographically, with no absolute physical barrier.

• Spatial Segregation: Each population occupies a distinct habitat or ecological niche within the broader range.

• Limited Gene Flow: Some interbreeding may occur at the borders, but strong selection or environmental differences reduce gene flow.

• Divergence: Over time, genetic differences accumulate, leading to reproductive isolation and the formation of new species.

How Does Parapatric Speciation Happen?

1. Environmental Gradient: A species spreads across a range with varying environmental conditions (e.g., soil type, altitude, temperature).

2. Local Adaptation: Subpopulations adapt to their specific habitats, developing unique traits.

3. Reduced Gene Flow: While individuals at the habitat boundaries may interbreed, strong selection against hybrids or migrants maintains separation.

4. Reproductive Isolation: Eventually, genetic divergence leads to the emergence of new species, even though their ranges are still contiguous.

Real-World Examples

• Grass species growing on contaminated versus uncontaminated soils: Some grasses evolve tolerance to heavy metals, leading to parapatric speciation along the soil gradient.

• Ring species such as the greenish warbler: Populations expand around a geographic barrier, with adjacent populations interbreeding, but the end populations become reproductively isolated.

Distinguishing Parapatric Speciation from Other Types

Importance of Parapatric Speciation

• Biodiversity: Explains the emergence of new species in landscapes without absolute barriers.

• Adaptation: Highlights the role of environmental gradients and local adaptation in driving speciation.

• Conservation: Understanding parapatric speciation can help in managing species that exist in fragmented or changing habitats.

Conclusion

When new species evolve in contiguous, yet spatially segregated habitats, the process is termed parapatric speciation. This unique form of speciation underscores the complexity of evolutionary processes and the diverse ways in which life adapts and diversifies across the planet.

Correct answer:
(4) Parapatric