Biology • Year 11 • Module 3 • Lesson 3
What is Biodiversity?
Apply the three biodiversity levels to data, interpret richness vs evenness, and reason about Australia’s megadiversity and the value of genetic diversity.
1. Interpret a species diversity comparison
The table below shows species counts in two forest communities. Use it to answer the questions. 8 marks
| Species | Community A (individual counts) | Community B (individual counts) |
|---|---|---|
| Species 1 | 25 | 88 |
| Species 2 | 24 | 4 |
| Species 3 | 23 | 4 |
| Species 4 | 22 | 4 |
| Total individuals | 94 | 100 |
1.1 State the species richness of Community A and Community B. 1 mark
1.2 Which community has greater species evenness? Justify your answer using the data. 2 marks
1.3 Which community has greater species diversity? Explain your reasoning, referring to both richness and evenness. 2 marks
1.4 Explain why simply reporting that “both communities have four species” is insufficient information for comparing their biodiversity. 2 marks
1.5 If a disturbance event removed 50% of Species 1 from Community B, predict which community would be more affected. Explain your reasoning. 1 mark
2. Interpret genetic diversity data
Use the scenario below to answer the questions. 6 marks
Scenario. Population X of a small marsupial contains 12 different alleles at a key immune-response gene. Population Y of the same species contains only 2 different alleles at the same gene. Both populations currently appear healthy. A new disease enters both habitats simultaneously.
2.1 Which population has greater genetic diversity? Explain your answer. 1 mark
2.2 Predict which population is more likely to have some individuals survive the new disease, and explain why. 2 marks
2.3 Explain what level of biodiversity this scenario is testing (genetic, species or ecosystem diversity) and why allele variation is relevant at this level. 2 marks
2.4 The lesson mentions that a koala population contains several alleles linked to immune response. Explain how this relates to the concept explored in this scenario. 1 mark
3. Australia’s megadiversity — cause-and-effect
Complete the cause-and-effect chain by filling in each empty box. The first box is done for you. 5 marks
Step 1: _________________________ between Australian lineages and those elsewhere reduced or stopped.
Step 2: Australian lineages (including monotremes, marsupials and specialised arid-zone species) evolved under distinctive conditions and _________________________ over millions of years.
Step 3: Many of these species are _________________________ — found only in Australia and nowhere else on Earth.
Outcome: Australia is described as a _________________________ country, holding roughly _________________________% of the world’s biodiversity despite covering only about 5% of Earth’s land.
Q1.1 — Species richness
Both Community A and Community B have a species richness of 4 (four different species each). [1 mark]
Q1.2 — Species evenness
Community A has greater species evenness [1]. In Community A, the four species have individual counts of 25, 24, 23 and 22 — nearly equal. In Community B, one species dominates with 88 individuals while the others each have only 4 — highly uneven [1].
Q1.3 — Greater species diversity
Community A has greater species diversity [1]. Both communities have equal richness (4 species), but Community A has much higher evenness because individuals are distributed nearly equally across all four species. Species diversity depends on both richness and evenness, and Community B’s very low evenness significantly reduces its overall species diversity despite having the same richness [1].
Q1.4 — Why richness alone is insufficient
Reporting only that both communities have four species tells us nothing about how individuals are distributed across those species (evenness) [1]. Community B is dominated by one species, which means only one species accounts for nearly all of the functional and ecological roles in that community. A simple species count masks this fundamental difference in the balance of the community, which is important for understanding stability, resilience and ecological function [1].
Q1.5 — Effect of disturbance
Community B would be more affected [1]. Because Species 1 makes up 88 out of 100 individuals (88%), removing 50% of Species 1 would eliminate approximately 44% of all individuals in that community and dramatically disrupt its function. Community A has no dominant species, so losing 50% of one species (about 12 individuals) has a much smaller proportional impact.
Q2.1 — Greater genetic diversity
Population X has greater genetic diversity [1] because it contains 12 different alleles at the immune-response gene, compared to only 2 alleles in Population Y. More allele variants = greater genetic diversity.
Q2.2 — Disease survival prediction
Population X is more likely to have some individuals survive [1]. With 12 different alleles, there is a greater probability that at least some individuals carry an allele that confers resistance or tolerance to the new disease. Population Y has only 2 alleles, so if neither confers resistance, the entire population could be lost [1].
Q2.3 — Biodiversity level
This scenario tests genetic diversity [1] — variation in alleles within a species or population. Allele variation is relevant at this level because it represents the raw material for adaptation and resilience within a population. A population with many alleles has a greater chance that some individuals will carry variants suited to new conditions, such as disease resistance [1].
Q2.4 — Koala example link
The koala example from the lesson illustrates the same principle [1]: a koala population with several alleles linked to immune response would be more resilient to new diseases than a population with reduced allele variety, just as Population X is more likely to survive than Population Y.
Q3 — Cause-and-effect chain (marking criteria)
- Step 1: gene flow / contact with other lineages / exchange of genetic material [1]
- Step 2: diverged / speciated / accumulated distinct adaptations [1]
- Step 3: endemic [1]
- Outcome: megadiverse; 10 [1 mark for megadiverse; 1 mark for 10%]