What is Biodiversity?
In 1972, the IUCN's global plant survey identified Australia as holding 7% of the world's flowering plant species on just 5% of Earth's land surface. Australian mammals represent 14% of global mammal species despite the continent covering only 5% of global land area. These figures made no sense until scientists understood that Australia's remarkable biodiversity stems not from its size, but from 45 million years of geographic isolation acting as a natural evolutionary experiment — producing species found nowhere else on Earth.
Practise this lesson
Four printable worksheets that build from the foundations up to exam-style questions — start at whatever level suits you.
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?
Know
- The three levels of biodiversity: genetic, species and ecosystem.
- What species richness and evenness contribute to species diversity.
- Why Australia is described as a megadiverse country.
Understand
- Why biodiversity is linked to resilience, ecological stability and usable genetic resources.
- How biodiversity connects to long evolutionary history and environmental change.
- Why biodiversity is more than just "counting species".
Can Do
- Distinguish the three biodiversity levels with examples.
- Explain whether a habitat can have high richness but low evenness.
- Use Australian examples to justify why biodiversity matters.
Core Content
Genes, species and ecosystems all matter
When the 1972 IUCN survey documented that Australia held 7% of global flowering plant species on only 5% of Earth's land, scientists needed a framework to explain what "more biodiversity" actually meant. If you counted only species numbers, you might miss that a eucalypt forest with 30 evenly distributed species can be more biodiverse than one with 50 species where a single dominant tree accounts for 90% of individuals. 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, measured at three distinct levels.
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.
- Genetic diversity is variation in alleles within a species or population. A population with many alleles has more raw material for future adaptation.
- Species diversity considers both species richness and species evenness. Richness counts how many species are present; evenness considers whether one species dominates or whether numbers are spread more evenly.
- Ecosystem diversity refers to the variety of habitats, communities and ecological processes, such as rainforest, coral reef, mangrove and arid grassland systems.
Biodiversity operates at three levels: genetic diversity (allele variation within a species), species diversity (richness plus evenness), and ecosystem diversity (variety of habitats, communities and ecological processes).
Biodiversity is layered: genes support species, and species are organised inside ecosystems.
Pause — copy the highlighted three-level definition into your book before the check below.
A koala population contains several different alleles linked to immune response. Which level of biodiversity does this best represent?
Stability, resilience and useful biological resources
We just saw that biodiversity exists at three levels — genes, species and ecosystems. That raises a question: why does any of this actually matter beyond classification? This card answers it → diversity at every level makes living systems more stable and more useful.
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.
Resilience
Diverse systems are more likely to recover after disturbance.
Resources
Genetic diversity supports future crop breeding and medicine discovery.
Intrinsic Value
Species and ecosystems also matter beyond direct human use.
Higher biodiversity improves resilience — diverse systems recover better from disturbance. Biodiversity also provides food, medicine, pollination and cultural value. Genetic diversity supports future adaptation; ecosystem diversity supports overlapping ecological roles.
Pause — copy the highlighted key points about why biodiversity matters before the check below.
An ecosystem with more species is always more resilient than one with fewer species, regardless of how the individuals are distributed.
Endemism, isolation and long evolutionary history
We just saw that biodiversity supports resilience and ecological stability. That sets up a question: what factors explain why some regions have so much more biodiversity than others? This card answers it → Australia's case shows that isolation and evolutionary time are the key drivers, not just land size.
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.
Australia's biodiversity is tied to isolation, time and the persistence of distinctive ecological niches.
Australia is megadiverse because of very high endemism and long evolutionary isolation after Gondwana separation. Endemic species = found only in one geographic location. Long isolation + stable environment = time for lineages to diverge (monotremes, marsupials). Repeated habitat disruption reduces biodiversity by removing niches and fragmenting populations.
Pause — copy the highlighted points about Australian endemism into your book before the check below.
What best explains why Australia has such high levels of endemic species?
Activities
Sort the Examples
Classify each example as genetic, species or ecosystem diversity, then justify one choice.
- A koala population contains several alleles linked to immune response.
- A woodland supports 42 bird species with relatively balanced numbers across the community.
- A region includes rainforest, estuary, mangrove and seagrass habitats.
- A coral reef has many fish species, but one species makes up 80% of individuals.
Richness vs Evenness
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.
Habitat A has 4 species distributed as 25, 24, 23, 22 individuals. Habitat B has 4 species distributed as 88, 4, 4, 4 individuals. Which habitat has higher species diversity?
Core Definitions
- Biodiversity is the variety of life on Earth at genetic, species and ecosystem levels.
- Species diversity depends on richness and evenness.
- Genetic diversity describes allele variation within a population.
Why It Matters
- Higher biodiversity generally improves resilience and ecological stability.
- Biodiversity provides food, medicine, pollination and cultural value.
- Australia is megadiverse because of high endemism and long evolutionary isolation.
HSC Distinctions
- Alleles = genetic diversity.
- Richness + evenness = species diversity.
- Habitats + communities + processes = ecosystem diversity.
Common Trap
- Do not define biodiversity only as "the number of species".
- A community can have high richness but low evenness.
- Australian biodiversity is linked to isolation and deep time.
A fresh set drawn from this lesson's question bank — feedback shown immediately. +5 XP per correct · +25 XP all correct
Pick your answer, then rate your confidence — that tells the system what to drill next.
UnderstandBand 3(3 marks) 1. Define biodiversity and distinguish between genetic diversity, species diversity and ecosystem diversity.
AnalyseBand 4–5(4 marks) 2. 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.
EvaluateBand 5–6(3 marks) 3. Explain why a habitat with fewer species could still be considered more biodiverse than a habitat with more species.
Show all answers
Multiple choice
MC answers and full explanations are shown inline as you complete each question. Use the retry button to attempt a fresh set from the lesson bank.
Activity 1 — Sort the Examples
1. Genetic diversity — allele variation within one koala species/population.
2. Species diversity (high richness AND high evenness) — 42 species spread relatively evenly.
3. Ecosystem diversity — multiple different habitat types in one region.
4. Species diversity with low evenness — high richness but dominated by one species, so diversity is reduced.
Activity 2 — Richness vs Evenness
Habitat A has greater species diversity. Both habitats have the same species richness (4 species), but Habitat A has far higher evenness — individuals are spread roughly equally across all four species. In Habitat B, one species dominates (88 of roughly 100 individuals), leaving the other three species very rare. A simple species count cannot capture this difference; diversity depends on both how many species are present and how evenly individuals are distributed among them.
Short Answer Model Responses
SAQ1 (3 marks): Biodiversity is the variety of life on Earth [1]. Genetic diversity refers to variation in alleles within a species or population [1]. Species diversity refers to the number of species present (richness) and how evenly individuals are distributed across them (evenness). Ecosystem diversity refers to the variety of habitats, communities and ecological processes in a region [1].
SAQ2 (4 marks): The claim is incomplete [1]. 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 [1]. For example, the Daintree preserves ancient rainforest lineages and highly specialised organisms that reflect deep evolutionary history, not just land size [1]. Therefore, land area matters less than isolation, niche diversity and evolutionary time [1].
SAQ3 (3 marks): A habitat with fewer species could still be more biodiverse if the individuals are distributed more evenly across those species [1]. A second habitat might have more species overall but be dominated by one species, giving it lower evenness and therefore lower species diversity [1]. Species diversity depends on both richness and evenness [1].
Three levels
Genetic (allele variation), Species (richness + evenness), Ecosystem (habitats + processes).
Why it matters
Resilience, resources (food/medicine), intrinsic value of species and ecosystems.
Australia
Megadiverse because of high endemism and long isolation from Gondwana — not just land size.
Most common exam trap
Defining biodiversity only as "the number of species" — richness without evenness misses the picture.
Rapid-fire questions on biodiversity levels, endemism and Australian examples. Beat the boss to bank a tier — gold (perfect + fast), silver (80%+), or bronze (cleared).
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 1972 IUCN survey that identified Australia as holding 7% of the world's flowering plant species and 14% of global mammal species on just 5% of Earth's land surface is only explicable through this three-level framework. Australia's figures reflect the outcome of 45 million years of geographic isolation after the Gondwana breakup — time for genetic diversity to accumulate within lineages, for species diversity to grow as populations diverged, and for ecosystem diversity to develop as organisms filled different niches. Measuring only "species count" would miss the genetic diversity within each unique lineage and the ecosystem-level variety of habitats from tropical rainforest to arid desert.