Year 8 Science · Unit 1 · Lesson 23
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Learning Goals
Match each species to its story
Write the matching letter in the middle column. Each letter is used once.
| Species | Letter | Its story |
|---|---|---|
| Tasmanian tiger (thylacine) | A. A termite-eater that survived only in small parts of Western Australia; predator control and habitat protection helped it. | |
| Bilby | B. Threatened by land clearing, the disease chlamydia, car strikes and dog attacks. | |
| Koala | C. A striped, dog-like carnivorous marsupial; the last known one died in a Hobart zoo in 1936. | |
| Numbat | D. A small frog raised in zoos and sanctuaries to create an insurance population. | |
| Corroboree frog | E. A rabbit-eared marsupial that once lived across most of Australia; foxes, cats and habitat loss have made it rare. |
1. Which species in the table is extinct? State what extinct means, and why that is different for conservation from a species that is still threatened.
Odd one out
In each row, three items belong together and one does not. Circle the odd one out and give your reason.
| Row | Items | Reason |
|---|---|---|
| 1 | chlamydia · planting local natives · car strikes · dog attacks | |
| 2 | land clearing for farms · a new road through a forest · longer droughts · a new housing estate | |
| 3 | a zoo breeding program · a national park · an Indigenous Protected Area · a nature reserve | |
| 4 | numbat · bilby · koala · fox |
Read the data
Scenario: releasing captive-bred bilbies
A conservation group bred 120 bilbies and released 40 at each of three sites. After 12 months, rangers counted how many of the released bilbies were still alive.
| Site | Habitat and predators | Released | Alive after 12 months |
|---|---|---|---|
| A | Native bushland; foxes baited, cats not controlled | 40 | 14 |
| B | Native bushland inside a fence that keeps out foxes and cats | 40 | 32 |
| C | Mostly cleared farmland; no fox or cat control | 40 | 3 |
Source: sample release records.
2. Calculate the percentage of released bilbies still alive at Site B and at Site C.
Site B % Site C %
3. The group’s newsletter says: “We bred 120 bilbies, so our program is a success.” Use Table 1 to explain why the number bred does not show success, and what the data suggest matters most.
Devils on an island
Scenario: Maria Island
Tasmanian devils are threatened by a contagious facial tumour disease that spreads when devils bite each other. In 2012, scientists released a small group of healthy, disease-free devils on Maria Island, which lies just off the east coast of Tasmania. Devils did not live on the island before, and the sea keeps them apart from sick devils on the main island of Tasmania.
4. Years later, researchers reported that the devils had eaten many of the island’s ground-nesting seabirds, including little penguins. Explain why the island was chosen to protect the devils. Then use an idea from the lesson to explain why the seabirds were so easily harmed, and what this shows about planning conservation.
5. A student says: “We should focus on saving cute animals like koalas and let ugly species disappear.” Evaluate this claim using Claim, Evidence and Reasoning.
Match each species to its story
Tasmanian tiger (thylacine) → C; Bilby → E; Koala → B; Numbat → A; Corroboree frog → D.
1. The Tasmanian tiger (thylacine). Extinct means the species is gone forever and will never return; a threatened species is still alive, so reducing its threats can still save it. [2 marks: 1 species, 1 difference]
Odd one out
Row 1: planting local natives (a conservation action; the others are threats to koalas). Row 2: longer droughts (climate change; the others are habitat loss from clearing land). Row 3: a zoo breeding program (the others protect habitat in the wild). Row 4: fox (an introduced species; the others are native marsupials).
Read the data
2. Site B: 32 ÷ 40 × 100 = 80%. Site C: 3 ÷ 40 × 100 = 7.5%. [2 marks]
3. Each site got 40 bilbies, but survivors ranged from 3 to 32, so breeding alone did not save them. Most survived in native habitat with foxes and cats kept out (Site B); almost none on cleared land with predators (Site C). Breeding works best when there is safe habitat to release animals into. [3 marks: 1 data comparison, 1 habitat, 1 predators]
Devils on an island
4. The sea keeps the healthy devils away from sick devils, so the disease cannot reach them (a disease-free insurance population). The seabirds had never lived with devils, so, like native mammals facing foxes and cats, they had no defences and no time to adapt. For the seabirds, the devils were an introduced predator. This shows that conservation plans must check how a new species will affect the ecosystem it is released into. [4 marks: 1 island keeps disease out, 1 no defences, 1 link to introduced predators, 1 planning point]
Show What You Know
5. Marking guide (points expected): 1 clear claim (disagree); 1 biodiversity makes ecosystems more stable and able to recover from change; 1 losing species weakens food webs, because species are linked; 1 named example and its role (e.g. the numbat eats termites; frogs are food for birds and snakes); 1 “cute” is not a scientific measure of importance; 1 conclusion: protect whole habitats, not only popular species. [6 marks]
Common error to watch for: in Q3, treating “more animals bred” as success. Success is animals surviving in the wild, which depends on safe habitat.