QUESTION 87 (6 marks)
Consider three hypothetical plant populations: P is divided by a new river barrier; Q contains groups in the same field that flower in different months; R occupies adjacent ends of a continuous moisture gradient and neighbouring groups mate more often than distant groups.
a) Match P, Q and R to allopatric, sympatric and parapatric speciation pathways. [3 marks]
b) For Q, explain how temporal isolation could eventually lead to separate species. [3 marks]
Practice marking scheme
Answer
a) P: allopatric; Q: sympatric; R: parapatric. b) Different flowering times reduce gene flow, allowing genetic divergence and eventual reproductive isolation.
Working
P has a geographic barrier; Q can diverge within the same geographic area through different reproductive timing; R has neighbouring ranges with limited exchange across an environmental gradient. In Q, non-overlapping flowering periods reduce opportunities for cross-fertilisation. Mutation, selection and drift can then cause the gene pools to diverge, eventually preventing interbreeding even if flowering timing later overlaps.
Marking criteria
- Matches P to allopatric. [1 mark]
- Matches Q to sympatric. [1 mark]
- Matches R to parapatric. [1 mark]
- Links different flowering periods to reduced interbreeding. [1 mark]
- Links reduced interbreeding to reduced gene flow/genetic divergence. [1 mark]
- Links accumulated divergence to reproductive isolation. [1 mark]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
View the QCAA syllabusCompare your working with the guide above.