Sympatric speciation
Laura Armstrong
Teacher
Recall Questions
This topic requires prior knowledge of allopatric speciation. You can test your knowledge on this below.
What causes allopatric speciation to begin?
A geographical barrier (e.g. river or mountain) that splits a population.
Why do separated populations become genetically different over time?
Because they experience different selection pressures and random mutations.
What must happen for two populations to be considered different species?
They can no longer interbreed to produce fertile offspring
Topic Explainer Video
What Is Speciation?
-
Speciation is the development of new species from a pre-existing species.
- New species are formed when populations become reproductively isolated and can no longer interbreed to produce fertile offspring.
Two Types of Speciation
|
Type of Speciation |
Cause of Isolation |
Example |
|---|---|---|
|
Allopatric |
Geographical separation |
River, mountain, motorway |
|
Sympatric |
Reproductive isolation without geographical separation |
Behavioural or genetic changes in the same habitat |
What Is Sympatric Speciation?
Sympatric speciation occurs when populations in the same geographical location become reproductively isolated due to biological changes, not physical barriers.
How Does Sympatric Speciation Happen?
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Mutation occurs in part of a population.
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The mutation may:
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Alter mating behaviour (e.g. courtship song).
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Change flowering or mating time (temporal isolation).
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Prevent gamete fusion (mechanical/genetic incompatibility).
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These changes lead to reproductive isolation even though they are living in the same habitat.
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Over generations, allele frequencies change due to:
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Natural selection.
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Genetic drift.
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Eventually, the two groups can no longer interbreed to produce fertile offspring, even if they live in the same habitat.
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A new species has formed = speciation.
Example of Sympatric Speciation
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Plants: A mutation causes a change in flowering time → certain individuals reproduce earlier than others.
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Over time, the early-flowering and late-flowering groups become reproductively isolated.
- Even though they live side by side, they form separate gene pools → new species arise.
Key Terms
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Speciation: The formation of new species from a pre-existing species.
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Sympatric speciation: Speciation occurring without geographical isolation, in the same habitat.
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Reproductive isolation: When groups of organisms can no longer breed to produce fertile offspring.
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Temporal isolation: When two populations reproduce at different times (e.g. season or time of day).
- Behavioural isolation: Differences in courtship or mating behaviours prevent interbreeding.
No answer provided.
Exam Tip
Students often confuse sympatric and allopatric speciation. If the question asks for sympatric, do not mention geographical barriers. Focus on reproductive isolation caused by mutation. Use the information provided in the question to try and figure out what led to reproductive isolation.
No answer provided.
Lord Howe Island possesses two species of palm tree which have arisen via sympatric speciation. The flowering times of the two species are different.
Using this information, suggest how these two species of palm tree arose by sympatric speciation. (5 marks)
1. Occurs in the same habitat / environment OR are not geographically isolated / separated
2. Mutations cause different flowering times
3. Reproductive separation / isolation OR No gene flow OR Gene pools remain separate
4. Different allele/s passed on / selected OR Change in frequency of allele/s
5. Natural selection (disruptive)
6. Eventually different species cannot interbreed to produce fertile offspring
Practice Question
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!