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DSE Biology – Biodiversity and Conservation Prep Guide (for tutors) | three levels, Lincoln index, species-area curve, four question types
Students read biodiversity as many species and conservation as planting trees. This lesson marks 40 animals, recaptures 35 and finds 14 marked, giving a population of 100, then cuts habitat area by ninety percent so species fall to about 56.2 percent, which makes protecting large habitat an arithmetic conclusion rather than a slogan.
Objectives — Students can: (1) separate genetic, species and ecosystem diversity and give a Hong Kong example of each; (2) use the Lincoln index with 40, 35 and 14 to get 100 and name three assumptions that bias the estimate; (3) use the species-area relationship with z equal to 0.25 to show that losing ninety percent of area leaves about 56.2 percent of species, and use that to judge replanting against keeping large habitat.
01 Prerequisites (3-minute check)
If any of these fails, fix it before the lesson starts.
| Skill | Quick check | Pass mark |
|---|---|---|
| Population and community | How does a population differ from a community? | A population is one species; a community is all species in the area |
| Energy flow | Where does energy go along a food chain? | It is lost as heat at each level, about a tenth passing on |
| Percentages | What percentage is 2.5 of 500? | 0.5 percent |
| Sampling bias | Why is sampling only beside the path unrepresentative? | Path edges are disturbed, so they misrepresent the interior |
02 Lesson flow (45 minutes)
| Time | Stage | Tutor does | Student does |
|---|---|---|---|
| 0-5 min | Prior knowledge check | Ask the four questions and write population and community | Answer orally and copy any wrong item |
| 5-15 min | Act one: three levels | Move from genes to species to ecosystems, one example each | Copy one example per level |
| 15-27 min | Act two: mark-recapture | Use 40, 35 and 14 to reach 100 | Recompute alone and write the assumptions |
| 27-37 min | Act three: area and species | Apply z equal to 0.25 to a ninety percent loss | Check 56.2 percent on a calculator |
| 37-42 min | Question practice | Model answer frames for the four types | Write one sentence per type |
| 42-45 min | Exit check | Hand out three items and collect them | Work alone with books closed |
03 Teaching script (read it out)
Scene 1: Act one: three levels, not just species count
At the genetic level we look at variation within a species, such as heat tolerance differing between corals on the same reef. At the species level we look at richness and evenness. At the ecosystem level we look at habitat types and the links between them.
The teaching point: each level can fall on its own. A wood may keep its species count while every tree belongs to one cloned line, so genetic diversity is already thin and one disease can take the stand.
Hong Kong examples: the Mai Po wetland for ecosystems, population divergence in the Hong Kong ricefish for genes, bird counts in country parks for species.
The teaching point: each level can fall on its own. A wood may keep its species count while every tree belongs to one cloned line, so genetic diversity is already thin and one disease can take the stand.
Hong Kong examples: the Mai Po wetland for ecosystems, population divergence in the Hong Kong ricefish for genes, bird counts in country parks for species.
Ask students to repeat: an unchanged species count does not mean diversity is intact.
Scene 2: Act two: mark-recapture is a proportion
Catch and mark 40, release them, then catch 35 and find 14 marked. The marked share of the whole population should equal the marked share of the second sample, so the population is 40 times 35 divided by 14, which is 100, and the marked share of the second sample is 40.0 percent.
Three assumptions: marks do not rub off, marked animals are as catchable as unmarked, and the population is closed to births, deaths and migration between visits.
Direction of bias matters: if marks rub off, R is too small and the estimate is too high; if marked animals become easier to catch, R is too large and the estimate is too low. Students reverse this constantly.
Three assumptions: marks do not rub off, marked animals are as catchable as unmarked, and the population is closed to births, deaths and migration between visits.
Direction of bias matters: if marks rub off, R is too small and the estimate is too high; if marked animals become easier to catch, R is too large and the estimate is too low. Students reverse this constantly.
Ask students to repeat: a low estimate means R was too large, so marked animals were easier to catch.
Scene 3: Act three: lose ninety percent of area, keep how many species
The species-area relationship is S equals c times A to the z, with z commonly 0.25. If area falls to 10 percent, species fall to 0.1 to the 0.25, about 0.5623, or roughly 56.2 percent.
In whole numbers: a site with 12 species keeps about 7 of them, and 3 of the originals are endemic, 25.0 percent, so losing them loses them everywhere.
Then fragmentation: the same 120 hectares cut into ten blocks multiplies the edge-to-area ratio tenfold, from 0.04 to 0.4, leaving a core of only 30 hectares, 25.0 percent. So replanting cannot undo an area effect, and keeping large continuous habitat always comes first.
In whole numbers: a site with 12 species keeps about 7 of them, and 3 of the originals are endemic, 25.0 percent, so losing them loses them everywhere.
Then fragmentation: the same 120 hectares cut into ten blocks multiplies the edge-to-area ratio tenfold, from 0.04 to 0.4, leaving a core of only 30 hectares, 25.0 percent. So replanting cannot undo an area effect, and keeping large continuous habitat always comes first.
Ask students to repeat: no amount of replanting buys back area.
04 Question types and worked steps
| Type | Example | Steps | Answer |
|---|---|---|---|
| Definitions with examples (3 marks) | One example per level | One sentence per level, with a named species or place | Genes, species, ecosystems |
| Calculation (4 marks) | Mark-recapture with 40, 35, 14 | Write the proportion, substitute, then state the unit | 100 animals |
| Assumptions and bias (4 marks) | Which broken assumption lowers the estimate | For each assumption ask whether R rises or falls | Marked animals easier to catch, R too large, estimate too low |
| Evaluation (6 marks) | Replanting trees is enough for conservation. Do you agree? | Give the benefit, then use area and fragmentation, then a conditional conclusion | Ninety percent area loss leaves 56.2 percent of species |
Sanity check (teach this): Three read-backs: (1) the estimate must exceed the second catch, so 100 beats 35, and a result below 35 means the proportion is upside down; (2) the species share after area loss must be under 1, so 56.2 percent is fine and anything above 100 percent inverts the exponent; (3) the sample covered only 0.5 percent, so the quadrat mean is an estimate and the word must appear in the answer.
05 Independent practice (3 questions)
| Question | Answer | What to watch |
|---|---|---|
| Mark 40, recapture 35 and find 14 marked: estimate the population | 100 | Check the proportion and the unit |
| If marks rub off, is the estimate high or low, and why? | High, because R falls | Check that R and N are seen as inversely related |
| Area falls 90 percent with z equal to 0.25: what share of species remains? | About 56.2 percent | Check the use of 0.1 to the 0.25 |
06 Common mistakes and what to say
| Mistake | Student writes | Say this |
|---|---|---|
| Merging the three levels | Biodiversity means having many different kinds of animal. | That is the species level only. Where are the gene and ecosystem levels? |
| Inverting the proportion | 40 times 14 divided by 35 | Your answer is smaller than the second catch, which is impossible. Check which number is the denominator. |
| Reversing the bias | Marks rub off, so the estimate came out too low. | Marks rubbing off means fewer marked animals, so R falls, the denominator falls and the estimate rises. You reversed it. |
| Conservation as tree planting | Conservation means planting more trees and going green. | Planting adds numbers, not area. Once habitat is cut, edge effects rise tenfold, so the answer must be about area. |
07 Homework (paper, section and question numbers)
- Redo this chapter (practice items 1-3) — Write all three, with the proportion shown in the calculation
- Evolution and natural selection — Link genetic diversity to selection in three sentences
- Biology chapter index — Pick one more chapter and draw the concept map only
08 Exit check (last 5 minutes)
| Question | Answer | Decision |
|---|---|---|
| Mark-recapture with 40, 35 and 14: the population is | 100 | Error: using the second catch as the denominator |
| Area down 90 percent with z of 0.25 leaves what share of species? | About 56.2 percent | Error: answering one tenth |
| Edge effect after cutting one block into ten | About ten times | Error: answering no change |
09 Tutor FAQ
Which year is this for?
The S6 ecology and conservation unit, best after energy flow is secure in S5.
Should the Shannon index be taught?
Not required for calculation, but evenness as a word prevents species count being treated as the whole story.
How do I fix the calculation quickly?
Three steps always: write the proportion, substitute, then check the answer exceeds the sample size.
Which local examples work?
Mai Po wetland, country parks and the Chinese white dolphin, one per level.
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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.