Biology • Year 11 • Module 3 • Lesson 13
Biogeography
Lock in the core vocabulary, the logic of geographic isolation and divergence, the major case studies (marsupials, Darwin’s finches, Wallace’s Line), and how distribution patterns constitute evidence for evolution.
1. Term–definition match
The eight definitions below are shuffled. In the right-hand column write the matching term from this list: biogeography, continental drift, Wallace’s Line, endemism, disjunct distribution, Gondwana, adaptive radiation, gene flow. 8 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 1.1 | The study of species distribution across geographic space and how those distributions reflect evolutionary history. | |
| 1.2 | The movement of Earth’s crustal plates over geological time, causing continents to separate and collide. | |
| 1.3 | A sharp faunal boundary in the Indonesian archipelago separating mainly Asian fauna to the west from mainly Australasian fauna to the east. | |
| 1.4 | The state of being unique to a defined geographic location and found nowhere else naturally. | |
| 1.5 | A pattern in which a species or group has a discontinuous range, with populations separated by a large gap. | |
| 1.6 | The ancient southern supercontinent that included what is now Australia, South America, Africa and Antarctica. | |
| 1.7 | The rapid diversification of a single ancestral lineage into multiple species occupying different ecological niches, commonly driven by island isolation. | |
| 1.8 | The movement of individuals and their alleles between populations, which can reduce genetic differences between isolated groups if it occurs, or allow divergence if it stops. |
2. True or false — with correction
For each statement, circle T or F. If the statement is false, write the corrected version. 8 marks (1 for T/F, 1 for correction where needed)
2.1 Biogeography shows that similar environments always produce identical sets of species. T / F
2.2 Geographic barriers reduce gene flow between populations, which can allow separated populations to diverge over time. T / F
2.3 Islands always have more species than nearby continental areas because they have unique habitats. T / F
2.4 Wallace’s Line separates mainly Asian fauna to the west from mainly Australasian fauna to the east, even between geographically close islands. T / F
3. Function recall
Answer each question in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
3.1 How does a geographic barrier such as an ocean lead to evolutionary divergence?
3.2 What do the related marsupial groups found in Australia and South America suggest about the geological history of those landmasses?
3.3 Why are Darwin’s finches on the Galapagos Islands an example of adaptive radiation?
3.4 Why does Wallace’s Line show that geographic closeness does not always mean evolutionary connectedness?
4. Cloze — complete the paragraph
Fill each blank with the correct word from the word bank. Use each word once only. 8 marks
Word bank: adaptive | ancestor | barriers | diverge | endemic | gene flow | Gondwana | isolation
Biogeography provides evidence for evolution by showing that distribution patterns reflect evolutionary history. When geographic such as oceans or mountain ranges arise, they reduce between populations. Without interbreeding, the isolated groups may over many generations due to different mutations, selection pressures and drift. Australian and South American marsupials share a origin: the marsupial was present on the ancient supercontinent before it separated. Darwin’s finches are an example of radiation driven by island . Islands often have a high proportion of species found nowhere else because isolation allows unique lineages to evolve.
Q1 — Term–definition matches
1.1 biogeography • 1.2 continental drift • 1.3 Wallace’s Line • 1.4 endemism • 1.5 disjunct distribution • 1.6 Gondwana • 1.7 adaptive radiation • 1.8 gene flow.
Q2 — True / False with correction
2.1 False. Correction: Biogeography reveals that geographic isolation, not just environment, determines species distribution. Similar climates can support very different species where continental history differs — e.g. Australian marsupials and African placentals occupy similar ecological roles in similar climates but evolved independently after continental separation.
2.2 True.
2.3 False. Correction: Islands typically have fewer species overall than nearby continental areas because colonisation is limited, but they often have a much higher proportion of endemic species because isolation promotes divergence in place.
2.4 True.
Q3.1 — Geographic barrier and divergence
A geographic barrier such as an ocean reduces or stops gene flow between populations on either side. Without interbreeding, the two groups accumulate different mutations and are subjected to different selection pressures and genetic drift, allowing them to diverge over generations into distinct lineages or species.
Q3.2 — Marsupials and Gondwana
Related marsupial groups in Australia and South America share a Gondwana origin: these landmasses were once connected as part of the ancient supercontinent Gondwana. The shared marsupial ancestor was present before separation, and after the continents drifted apart, the marsupial lineages on each landmass diverged independently from this shared ancestor.
Q3.3 — Darwin’s finches and adaptive radiation
Darwin’s finches on the Galapagos Islands are an example of adaptive radiation because a single colonising ancestral species diversified into multiple species with different beak forms adapted to different food sources (seeds, insects, cacti), driven by island isolation and access to different ecological niches without competition from mainland species.
Q3.4 — Wallace’s Line and evolutionary connectedness
Wallace’s Line is caused by deep-water barriers that prevented the movement of terrestrial organisms even between geographically nearby islands. Lineages on either side of the line experienced long periods of isolation and evolved separately, so islands that are geographically close still have very different faunas — demonstrating that current geographic distance is less important than historical barriers to movement.
Q4 — Cloze answers (in order of blanks)
barriers • gene flow • diverge • Gondwana • ancestor • Gondwana • adaptive • isolation • endemic
Note: the word bank has 8 words; “Gondwana” fills two blanks (marsupial origin and supercontinent name), and “adaptive radiation driven by island isolation” uses “adaptive” and “isolation” from the word bank.