Year 10 Science · Unit 1 · Lesson 15
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Learning Goals
Compare two
Complete the table to compare allopatric and sympatric speciation.
| Feature | Allopatric speciation | Sympatric speciation |
|---|---|---|
| Does a physical barrier divide the population? | ||
| Does gene flow stop between groups? | ||
| How common is this type? | ||
| Australian or global example | ||
| What ultimately causes reproductive isolation? |
Real-world context
Approximately 50 million years ago, Australia broke away from Gondwana and drifted northward, becoming completely isolated from other landmasses. At the time, marsupial mammals were already present on the landmass. As Australia moved away, isolated from the placental mammals that dominated other continents, marsupials diversified to fill every ecological niche. Today, 85% of Australia's mammal species are found nowhere else on Earth. Different possum species have even diverged on opposite sides of the Great Dividing Range in eastern Australia, with each population adapting to its local environment.
(a) Explain, step by step, how the separation of Australia from Gondwana 50 million years ago ultimately led to 85% of Australia's mammals being unique species today. Use the terms: geographic isolation, gene flow, natural selection, reproductive isolation.
(b) The Great Dividing Range has separated possum populations on its eastern and western slopes. Why might these two possum groups eventually become separate species, even though they are the same species today?
1. Darwin's finches on the Galapagos Islands all descended from a single mainland South American ancestor. How does allopatric speciation explain the 14 different finch species found on different islands today?
Wrap Up
In one sentence, what was the main idea of this lesson?