- The speciation in which a population splits into two geographically isolated populations experience dissimilar selective pressure and genetic drift is known
as
(1) sympatric speciation. (2) parapatric speciation.
(3) peripatric speciation. (4) allopatric speciation.What is Allopatric Speciation?
Allopatric speciation, also known as geographic speciation, occurs when a physical barrier—such as a mountain range, river, or ocean—divides a population. This barrier prevents gene flow between the separated groups, allowing them to evolve independently. As each population adapts to its unique environment and accumulates genetic differences, reproductive isolation eventually develops, even if the physical barrier is later removed.
Key Features of Allopatric Speciation
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Geographic Isolation: A physical barrier separates the original population into two or more groups.
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Dissimilar Selective Pressures: Each isolated population faces different environmental challenges, leading to natural selection for different traits.
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Genetic Drift: Random changes in allele frequencies can have a significant impact, especially in small populations.
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Reproductive Isolation: Over time, genetic differences accumulate to the point where individuals from different populations can no longer interbreed successfully.
The Process of Allopatric Speciation
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Initial Separation: A geographic event or change, such as the formation of a river or a landslide, divides a population into isolated groups.
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Independent Evolution: With no gene flow between groups, each population evolves independently. Natural selection, mutation, and genetic drift all play roles in shaping the genetic makeup of each group.
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Divergence: As generations pass, the genetic and phenotypic differences between the populations increase.
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Reproductive Isolation: Eventually, the differences become so pronounced that even if the populations come back into contact, they are unable to interbreed and produce fertile offspring. At this point, speciation is complete.
Real-World Examples
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Darwin’s Finches: On the Galápagos Islands, finch populations were separated by water barriers. Over time, they evolved different beak shapes and sizes to exploit various food sources, leading to the formation of multiple distinct species.
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Squirrels in the Grand Canyon: The Kaibab and Abert’s squirrels live on opposite rims of the Grand Canyon. Geographic isolation has led to differences in coloration, behavior, and genetics, resulting in two separate species.
Why Geographic Isolation is So Powerful
Geographic isolation is a fundamental driver of biodiversity. By preventing gene flow, it allows populations to explore new evolutionary paths. Natural selection acts on the unique challenges of each environment, while genetic drift can cause rapid changes in small, isolated groups. Over time, these forces combine to create new species adapted to their specific habitats.
Allopatric vs. Other Types of Speciation
Type of Speciation Key Feature Example Allopatric Geographic isolation Darwin’s finches, Grand Canyon squirrels Sympatric No geographic barrier; speciation in same area Polyploidy in plants, cichlid fish Parapatric Neighboring populations with limited gene flow Grasses along mine tailings Peripatric Small population isolated at the edge of range Island colonization by insects Allopatric speciation is distinguished by the presence of a clear geographic barrier, while sympatric speciation occurs without physical separation. Parapatric and peripatric speciation involve partial isolation or small peripheral populations, but allopatric speciation remains the classic model for understanding how physical barriers drive the formation of new species.
The Role of Genetic Drift and Natural Selection
Both genetic drift and natural selection are integral to allopatric speciation:
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Genetic Drift: Especially in small isolated populations, random changes in allele frequencies can lead to rapid divergence from the original population.
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Natural Selection: Different environments exert different selective pressures, favoring traits that enhance survival and reproduction in each habitat.
Over time, these forces lead to the accumulation of genetic differences that result in reproductive isolation.
The Importance of Allopatric Speciation in Evolution
Allopatric speciation is responsible for much of the planet’s biodiversity. It explains how new species arise following the formation of physical barriers and why isolated environments, such as islands and mountain ranges, are often hotspots for unique species.
Conclusion
When a population splits into two geographically isolated groups that experience dissimilar selective pressures and genetic drift, the process is known as allopatric speciation. This powerful evolutionary mechanism is central to the origin of new species and the incredible diversity of life on Earth.
Correct answer:
(4) Allopatric speciation. -
