Australia holds roughly 10% of the world's biodiversity despite covering only about 5% of Earth's land. That claim only makes sense if we know what biodiversity actually means, how scientists describe it, and why it matters for the stability of living systems.
Use the PDF for classwork, homework or revision. It includes key ideas, activities, questions, an extend task and success-criteria proof.
1. If one forest has more species than another forest, does that automatically mean it has more biodiversity?
2. Why might a region with a very long, stable evolutionary history hold more biodiversity than a region that has been repeatedly disrupted?
Type your initial thinking here. You will revisit these ideas at the end of the lesson.
Write your initial thinking in your book, then come back and compare it with your end-of-lesson response.
Core Content
Genes, species and ecosystems all matter
Biodiversity is not just the number of living things in one place. It is the variety of life across populations, species and whole ecological systems.
That definition matters because HSC questions often test whether students can separate levels of biodiversity cleanly. If we only talk about "lots of organisms", we miss the key idea that biodiversity can exist inside a species, between species, and across habitats.
Stability, resilience and useful biological resources
Biodiversity matters because ecosystems with more variety are usually better able to absorb disturbance and continue functioning.
When populations hold more genetic variation, they are more likely to include traits that help some individuals survive disease, drought or temperature change. When ecosystems contain many species performing overlapping roles, the loss of one species may not collapse the whole system immediately. Biodiversity also matters to humans because it provides food crops, medicines, pollination, soil health and cultural value.
Endemism, isolation and long evolutionary history
Australia is megadiverse not just because it has many species, but because so many of them evolved in long isolation and are found nowhere else.
Australia contains an exceptionally high proportion of endemic mammals, birds, reptiles and plants. Its long separation from other landmasses meant lineages could continue evolving under distinctive conditions, producing organisms such as monotremes, marsupials and highly specialised arid-zone species.
Longer periods of environmental stability can preserve more evolutionary history. In contrast, repeated disruption or simplification of habitats tends to reduce biodiversity by removing niches and fragmenting populations.
Activities
Classify each example below as genetic, species or ecosystem diversity, then justify one of your choices.
Type your classifications and reasoning here.
Answer in your book, then use this box for corrections or summary notes.
Habitat A and Habitat B each contain four species. Their individual counts are shown below.
Explain which habitat has greater species diversity and why a simple species count does not fully answer the question.
Focus on the role of evenness in your explanation.
Write your paragraph in your book, then use this space for any final refinement.
The first question should now feel easier to answer precisely: more species does not automatically mean more biodiversity, because species diversity depends on both richness and evenness, and biodiversity also includes genetic and ecosystem diversity.
The second question points to a core Module 3 idea: long evolutionary history and relative environmental stability can preserve lineages and allow divergence to accumulate. Australia's biodiversity is inseparable from that history.
Assessment
Choose one answer, then read the explanation
1. Which statement best defines genetic diversity?
2. A habitat contains 15 species, but one species makes up 90% of all individuals. Which conclusion is most accurate?
3. Why is Australia considered a megadiverse country?
4. Which option is the best example of ecosystem diversity?
5. Why can high genetic diversity increase a population's chance of persistence?
1. Define biodiversity and distinguish between genetic diversity, species diversity and ecosystem diversity. (3 marks)
1 mark: biodiversity definition | 1 mark: genetic diversity | 1 mark: species vs ecosystem diversity distinction
2. Explain why a habitat with fewer species could still be considered more biodiverse than a habitat with more species. (3 marks)
1 mark: species richness | 1 mark: evenness | 1 mark: explicit comparison/judgement
3. Evaluate the claim that Australia's biodiversity is mainly the result of having a large land area. In your answer, use the Daintree or another Australian example to justify your judgement. (4 marks)
1 mark: judgement | 1 mark: role of isolation/evolutionary history | 1 mark: relevant Australian example | 1 mark: evaluative explanation
Answers
SA1: Biodiversity is the variety of life on Earth. Genetic diversity refers to variation in alleles within a species or population. Species diversity refers to the number of species present and how evenly individuals are distributed across them. Ecosystem diversity refers to the variety of habitats, communities and ecological processes in a region.
SA2: A habitat with fewer species could still be more biodiverse if the individuals are distributed more evenly across those species. A second habitat might have more species overall but be dominated by one species, giving it lower evenness and therefore lower species diversity.
SA3: The claim is incomplete. Large area alone does not explain Australia's biodiversity. Australia's long isolation after separating from Gondwana allowed distinctive lineages to persist and diverge, producing high endemism. For example, the Daintree preserves ancient rainforest lineages and highly specialised organisms that reflect deep evolutionary history, not just land size. Therefore, land area matters less than isolation, niche diversity and evolutionary time.
Say each answer out loud before checking the prompt below it