DP Biology HL A4.2 Conservation of Biodiversity

DP Biology HL A4.2 Conservation of Biodiversity - Full notes

RevisionPrep

DP Biology HL | A4.2 Conservation of Biodiversity

DP BIOLOGY · THEME A: UNITY AND DIVERSITY

A4.2

Conservation of Biodiversity

Full notes for HL · IB-style

Contents

1	What biodiversity is
2	Measuring biodiversity
3	Past and present mass extinctions
4	Causes of the current biodiversity crisis
5	Conservation in situ and ex situ
6	Prioritizing species and areas for conservation
7	Biodiversity hotspots
8	Evidence for a biodiversity crisis
9	Causes of biodiversity loss: HIPPO
10	Climate change and biodiversity
11	Invasive species
12	In situ conservation
13	Ex situ conservation
14	Rewilding and habitat restoration
15	Keystone species and conservation priorities
16	The EDGE of Existence programme
17	Measuring biodiversity in the field
18	Sustainable use of resources
19	International agreements
20	Mixed review: worked problems
21	Additional exam-style practice
22	Genetic diversity within species
23	Ecosystem services
24	Common misconceptions and links
25	Exam-style question with markscheme
26	Check your understanding
27	Summary and topic map

These are full teaching notes. Read each section in order, try the Think about it question before you read on, and do every Quick check before moving to the next section.

Before you start

Rate yourself on each statement now, and again after you've worked through the notes. Shade R (not yet), A (getting there) or G (confident).

I can…	R	A	G
define biodiversity at the levels of ecosystem, species and genetic diversity
explain how biodiversity is measured and the challenges of measuring it
outline evidence for past mass extinctions and the current biodiversity crisis
explain the causes of biodiversity loss, including overexploitation, habitat loss, invasive species, pollution and climate change
evaluate in situ and ex situ conservation
explain the EDGE approach to prioritizing species

There is no additional HL content in this subtopic. SL and HL students study the same material.

Guiding questions

Why is biodiversity being lost so quickly, and why does it matter? How can we decide which species and places to protect first?

How this topic is examined

A4.2 is examined through data on species decline, case studies of extinction or habitat loss, and evaluation of conservation strategies. Paper 2 data questions often show population or deforestation trends.

Strong answers name specific species and places, link each cause to its mechanism, and evaluate conservation approaches with their strengths and limitations.

Command term	What the examiner wants
State / Identify	a brief answer with no explanation needed
Outline	a brief account or summary
Describe	a detailed account, including trends or features, without reasons
Explain	a detailed account including causes, reasons or mechanisms
Distinguish / Compare and contrast	give the differences (and similarities), point by point
Calculate	a numerical answer with working and units
Deduce / Suggest	reach a conclusion from data; propose a reasonable explanation
Evaluate / Discuss	weigh strengths and limitations and reach a judgement

How to use these notes

Each section teaches one part of the syllabus in full. You'll see these boxes throughout; each has one job:

Box	What it's for
Think about it	a question to get you thinking before a section; the answer comes in the section
Key point	the one idea you must not forget
Common mistake	an error examiners see every year, and how to avoid it
In the real world	where the biology shows up outside the classroom
Try this	something quick you can do yourself to test the idea
Worked example	full solutions with IB-style marks (M1 method, A1 answer, R1 reasoning)
Quick check	short questions to test yourself at the end of each section

1 What biodiversity is

Diversity at three levels: ecosystems, species and genes.

Think about it

If every tiger in the world were genetically identical, would the species be safe? What could go wrong?

Biodiversity is the variety of life in all its forms, levels and combinations. It includes three levels.

Ecosystem diversity is the variety of habitats and ecosystems in an area: forests, wetlands, grasslands, coral reefs and so on.

Species diversity is the variety of species in an area. It has two components: richness (the number of different species) and evenness (how evenly individuals are spread among those species).

Genetic diversity is the variety of alleles within a species. Populations with high genetic diversity are more likely to contain individuals that can survive new diseases or environmental change; populations with low genetic diversity (after a population bottleneck) are vulnerable.

Level	Meaning	Example
Ecosystem	variety of habitats and ecosystems	Western Ghats forests, mangroves, grasslands
Species	variety of species (richness and evenness)	tropical rainforest with thousands of tree species
Genetic	variety of alleles within a species	different varieties of rice

In the real world

Cheetahs have extremely low genetic diversity, probably because their numbers crashed to a few individuals about 12 000 years ago. Skin grafts between unrelated cheetahs are often accepted, as between identical twins, which shows how genetically similar they are.

Quick check

1. Name the three levels of biodiversity.

2. Distinguish richness and evenness.

3. Why is genetic diversity important?

Answers: 1. ecosystem, species, genetic 2. richness: number of species; evenness: how evenly individuals are distributed 3. allows populations to adapt to disease and change

2 Measuring biodiversity

Counting life is harder than it sounds.

Scientists estimate that there are about 8.7 million eukaryotic species, but fewer than 2 million have been described. Most undiscovered species are small: insects, nematodes, fungi and microorganisms, especially in tropical forests and the deep sea.

Measuring biodiversity is challenging because many species are hard to find, identify or tell apart; some live in inaccessible places; taxonomists are scarce; and species definitions can be unclear. Methods include field surveys (quadrats, transects, traps), citizen science projects, DNA barcoding and environmental DNA (detecting species from DNA in water or soil samples).

Simpson's reciprocal index combines richness and evenness: D = N(N − 1) ÷ Σn(n − 1), where N is the total number of individuals and n the number of each species. Higher values mean greater diversity.

WORKED EXAMPLE 1 Simpson's reciprocal index

A pond sample contains 10 water beetles, 6 snails and 4 dragonfly larvae (N = 20). Calculate Simpson's reciprocal index.

Solution

Σn(n − 1) = 10×9 + 6×5 + 4×3 = 90 + 30 + 12 = 132M1

N(N − 1) = 20 × 19 = 380M1

D = 380 ÷ 132 = 2.88A1

Compare D values between sites sampled in the same way. A site with the same species but very uneven numbers would have a lower D.

Quick check

1. Why are most undescribed species small?

2. What two components does Simpson's index combine?

Answers: 1. they are hard to find and identify 2. richness and evenness

3 Past and present mass extinctions

Life has survived five mass extinctions. Many scientists think a sixth is under way.

Extinction is the permanent disappearance of a species. Extinctions occur naturally all the time, at a low 'background' rate. A mass extinction is a period when a large proportion of species, at least 75%, become extinct in a geologically short time.

The fossil record shows five mass extinctions in the last 500 million years. The largest, at the end of the Permian about 252 million years ago, wiped out about 90% of marine species, probably due to massive volcanic eruptions and climate change. The most recent, at the end of the Cretaceous about 66 million years ago, killed the non-avian dinosaurs, probably due to an asteroid impact.

Many scientists argue that a sixth mass extinction is under way, caused by human activity. Current extinction rates are estimated to be tens to hundreds of times higher than background rates. Since 1970, monitored populations of vertebrates have declined on average by about 70% (WWF Living Planet Index).

Figure 1. The Living Planet Index shows an average decline of about 70% in monitored vertebrate populations since 1970.

Examples of human-caused extinctions include the dodo (Mauritius, hunted and attacked by introduced animals, extinct by about 1680), the passenger pigeon (North America, once billions, hunted to extinction by 1914) and Steller's sea cow (hunted to extinction within 27 years of its discovery in 1741).

Quick check

1. Define mass extinction.

2. What caused the extinction at the end of the Cretaceous?

3. Give an example of a species made extinct by humans.

Answers: 1. loss of at least 75% of species in a short geological time 2. probably an asteroid impact 3. dodo, passenger pigeon, Steller's sea cow

4 Causes of the current biodiversity crisis

Habitat loss, overexploitation, invasive species, pollution and climate change.

Habitat loss and fragmentation is the biggest cause. Forests are cleared for agriculture (cattle ranching, soybean, palm oil), cities and roads. Fragmentation leaves small, isolated patches that cannot support large populations. Example: clearing of lowland rainforest in Borneo and Sumatra for oil palm plantations has destroyed habitat for orangutans, now critically endangered.

Overexploitation: hunting, fishing and harvesting faster than populations can recover. Example: the collapse of the Atlantic cod fishery off Newfoundland in 1992; poaching of rhinos for horn and elephants for ivory.

Invasive alien species: species introduced to new areas where they compete with, prey on or spread disease to native species. Example: rats, cats and stoats introduced to New Zealand have driven many flightless birds to extinction; the brown tree snake eliminated most native forest birds on Guam.

Pollution: pesticides, plastics, nutrient run-off (causing eutrophication) and oil spills. Climate change: shifting habitats, coral bleaching, and changes in the timing of seasonal events (D4.3).

Underlying all these causes is the growth of the human population and of consumption.

Cause	Mechanism	Example
Habitat loss	destroys and fragments habitats	oil palm in Borneo; orangutans
Overexploitation	harvest faster than reproduction	Atlantic cod; rhino poaching
Invasive species	competition, predation, disease	rats and stoats in New Zealand
Pollution	toxins, eutrophication, plastics	DDT and birds of prey
Climate change	habitats shift faster than species adapt	coral bleaching

Quick check

1. Which cause of biodiversity loss is the largest?

2. How do invasive species harm native species?

Answers: 1. habitat loss 2. competition, predation, disease

5 Conservation in situ and ex situ

Protect species where they live, or save them elsewhere.

5.1 In situ conservation

In situ conservation protects species in their natural habitat. It includes national parks, nature reserves and marine protected areas, as well as managing habitats (controlling invasive species, restoring degraded land) and protecting wildlife corridors that connect fragmented habitats. Rewilding restores ecosystems by reintroducing species and allowing natural processes to recover, such as the reintroduction of wolves to Yellowstone in 1995, which restored trophic cascades.

Advantages: species remain in the environment to which they are adapted; whole ecosystems and their interactions are protected; many species are conserved at once. Disadvantages: reserves can be expensive to manage and police; they may be too small; and they are vulnerable to climate change.

5.2 Ex situ conservation

Ex situ conservation protects species outside their natural habitat: in zoos, botanic gardens, aquariums and seed banks. Zoos run captive breeding programmes with careful management of genetic diversity, and some species are reintroduced to the wild. The Svalbard Global Seed Vault in Norway stores over a million seed samples of crop varieties as insurance against loss. Frozen collections store sperm, eggs and embryos.

Advantages: protects species that would otherwise go extinct; allows research and education. Disadvantages: small captive populations lose genetic diversity; animals may lose natural behaviours; reintroduction often fails if the threats in the wild remain.

	In situ	Ex situ
Where	natural habitat	zoos, botanic gardens, seed banks
Protects	species and their ecosystem	individual species or genetic material
Strength	natural behaviour, many species at once	rescue of critically endangered species
Weakness	expensive, threats remain	low genetic diversity, artificial conditions

In the real world

The Arabian oryx was extinct in the wild by 1972. Captive breeding in zoos built up a population that was reintroduced to Oman and Saudi Arabia from 1982; there are now over 1 000 in the wild.

Quick check

1. Define in situ conservation.

2. Give two advantages of seed banks.

Answers: 1. protecting species in their natural habitat 2. store genetic diversity cheaply; insurance against crop loss

6 Prioritizing species and areas for conservation

With limited money, which species should come first?

Resources for conservation are limited, so priorities must be set. One approach is to protect biodiversity hotspots: areas with very high numbers of endemic species (found nowhere else) that are under threat, such as the Western Ghats in India, Madagascar and the tropical Andes.

The EDGE of Existence programme (Zoological Society of London) prioritizes species that are Evolutionarily Distinct and Globally Endangered. Evolutionary distinctiveness measures how much unique evolutionary history a species represents (how few close relatives it has). A species such as the aye-aye of Madagascar or the Chinese giant salamander has no close relatives, so its extinction would lose a large branch of the tree of life. Combining distinctiveness with threat status gives an EDGE score.

Other approaches focus on flagship species (charismatic species such as tigers and pandas that attract funding) and keystone species (species with a disproportionately large effect on their ecosystem, such as sea otters, which control sea urchins and so protect kelp forests).

Key point

Conservation succeeds when the causes of decline are removed. Protecting habitat, reducing exploitation and controlling invasive species usually matter more than any single rescue effort.

7 Biodiversity hotspots

Where diversity is concentrated.

Biodiversity hotspots are regions with very high numbers of endemic species (found nowhere else) that are also seriously threatened. They cover about 2.5% of land but hold about half of all endemic plant species. Examples: Madagascar, the tropical Andes, the Western Ghats.

WORKED EXAMPLE 2 Hotspots (standard)

Explain why conservation efforts often focus on hotspots.

Solution

High numbers of endemic speciesR1

High threat, so protecting a small area saves many speciesR1

Quick check

1. Define endemic species.

Answers: 1. a species found naturally in only one region

8 Evidence for a biodiversity crisis

Extinction rates.

Current extinction rates are estimated to be 100–1000 times the background rate. Evidence comes from species assessments (IUCN Red List), population monitoring (Living Planet Index shows average declines of about 69% in monitored vertebrate populations since 1970), and loss of habitats.

WORKED EXAMPLE 3 Evidence (standard)

Give two types of evidence for the current biodiversity crisis.

Solution

Population surveys showing declinesR1

Increasing numbers of threatened species on the Red ListR1

In the real world

The Living Planet Index tracks tens of thousands of populations of vertebrates worldwide and is updated every two years.

9 Causes of biodiversity loss: HIPPO

Five main threats.

Threat	Description	Example
Habitat loss	deforestation, urbanization, agriculture	orangutan habitat lost to oil palm
Invasive species	introduced species outcompete or prey on natives	cane toads in Australia
Pollution	chemicals, plastics, nutrients	eutrophication, microplastics
Population (human)	increasing demand for resources	expansion of farmland
Overexploitation	overfishing, hunting, logging	Atlantic cod collapse

WORKED EXAMPLE 4 Overexploitation (standard)

Explain how overfishing led to the collapse of Atlantic cod.

Solution

Fish removed faster than the population could reproduceR1

Breeding stock fell below a sustainable levelR1

10 Climate change and biodiversity

Shifting ranges.

Climate change shifts species' ranges towards the poles and higher altitudes, causes mismatches in timing (phenology), and threatens species with limited ability to move. Coral reefs suffer bleaching as ocean temperatures rise.

WORKED EXAMPLE 5 Coral bleaching (standard)

Explain coral bleaching.

Solution

High temperatures cause corals to expel their symbiotic algae (zooxanthellae)R1

Corals lose colour and their main energy sourceR1

11 Invasive species

Introduced and harmful.

Invasive alien species spread rapidly in new habitats, often because they lack natural predators, competitors or diseases. They compete with, prey on or spread disease to native species.

WORKED EXAMPLE 6 Cane toads (exam level)

Explain why cane toads became a problem in Australia.

Solution

Introduced without natural predatorsR1

Toxic to native predators that eat them; compete with native speciesR1

Quick check

1. Suggest one way to control an invasive species.

Answers: 1. biological control, culling, trapping, or preventing introduction

12 In situ conservation

Protecting species in their habitats.

In situ conservation protects species in their natural habitats through national parks, nature reserves, marine protected areas, and habitat restoration. It maintains ecological interactions and allows evolution to continue.

WORKED EXAMPLE 7 Advantages (standard)

State two advantages of in situ conservation.

Solution

Species remain in their natural habitat with natural interactionsR1

Many species protected at onceR1

13 Ex situ conservation

Zoos, botanic gardens and seed banks.

Ex situ conservation protects species outside their habitats: captive breeding in zoos, botanic gardens, and seed and gene banks (such as the Svalbard Global Seed Vault). It is useful when habitats are destroyed or populations are very small.

WORKED EXAMPLE 8 Limitations (exam level)

Give two limitations of captive breeding programmes.

Solution

Small populations lose genetic diversity (inbreeding)R1

Animals may lack survival skills when released; habitat may no longer existR1

In the real world

The Svalbard Global Seed Vault in Norway stores over a million seed samples from almost every country as insurance against crop loss.

14 Rewilding and habitat restoration

Reversing losses.

Rewilding restores natural processes, often by reintroducing key species (such as wolves in Yellowstone or beavers in the UK). Wolves reduced elk overgrazing, allowing vegetation and other species to recover (a trophic cascade).

WORKED EXAMPLE 9 Trophic cascade (standard)

Explain how reintroducing wolves affected Yellowstone's rivers.

Solution

Wolves reduced elk browsing near riversR1

Willows and aspens recovered, stabilizing riverbanksR1

15 Keystone species and conservation priorities

Disproportionate effects.

A keystone species has a large effect on its ecosystem relative to its abundance (sea otters control sea urchins, protecting kelp forests). Protecting keystone and flagship species (charismatic species that attract funding, such as pandas) can protect whole ecosystems.

Quick check

1. Distinguish keystone and flagship species.

Answers: 1. keystone: large ecological role; flagship: charismatic, raises awareness and funds

16 The EDGE of Existence programme

Unique evolutionary history.

EDGE prioritizes species that are Evolutionarily Distinct and Globally Endangered, such as the aye-aye, the pangolin and the axolotl, because losing them removes unique evolutionary lineages.

WORKED EXAMPLE 10 EDGE (standard)

Explain why the EDGE approach may prioritize an unattractive species over a charismatic one.

Solution

It values evolutionary distinctiveness and threat, not appearanceR1

17 Measuring biodiversity in the field

Quadrats and indices.

Biodiversity is assessed by sampling: quadrats for plants and sessile animals, transects across gradients, pitfall traps and sweep nets for invertebrates. Species richness and Simpson's index summarize diversity; repeated surveys monitor change.

WORKED EXAMPLE 11 Sampling (standard)

Why are quadrats placed randomly?

Solution

To avoid bias and obtain representative samplesR1

18 Sustainable use of resources

Meeting needs without depletion.

Sustainable harvesting keeps exploitation below the maximum sustainable yield: fishing quotas, minimum mesh sizes, closed seasons, selective logging and replanting. Certification schemes (MSC, FSC) help consumers choose sustainable products.

Quick check

1. How do minimum mesh sizes help sustain fish stocks?

Answers: 1. young fish escape and can reproduce

19 International agreements

Global cooperation.

CITES regulates international trade in endangered species; the Convention on Biological Diversity sets global targets, including the '30 by 30' goal (protecting 30% of land and sea by 2030); the Ramsar Convention protects wetlands.

WORKED EXAMPLE 12 CITES (standard)

What does CITES regulate?

Solution

International trade in endangered species and their productsA1

20 Mixed review: worked problems

Bringing the ideas together.

WORKED EXAMPLE 13 Mixed problem (exam level)

Evaluate the use of zoos in conservation.

Solution

Captive breeding and reintroduction; education and researchR1 R1

Limited genetic diversity; animals may not adapt to the wild; does not protect habitatsR1

21 Additional exam-style practice

Paper 1 and Paper 2.

WORKED EXAMPLE 14 Paper 1 question (standard)

Which is an example of in situ conservation? A. seed bank B. captive breeding in a zoo C. national park D. botanic garden

Solution

CA1

WORKED EXAMPLE 15 Paper 2 question (exam level)

Outline three causes of the current biodiversity crisis.

Solution

Habitat destructionR1

Invasive speciesR1

Overexploitation, pollution or climate changeR1

22 Genetic diversity within species

Why small populations are at risk.

Small populations lose genetic diversity through genetic drift and inbreeding, reducing their ability to adapt to change and increasing the frequency of harmful recessive alleles. Wildlife corridors connect fragmented habitats to maintain gene flow.

Quick check

1. How do wildlife corridors help conserve species?

Answers: 1. allow movement and gene flow between populations

23 Ecosystem services

Why biodiversity matters to humans.

Biodiversity provides ecosystem services: provisioning (food, timber, medicines), regulating (pollination, climate regulation, water purification), supporting (soil formation, nutrient cycling) and cultural (recreation, spiritual value).

Quick check

1. Give an example of a regulating ecosystem service.

Answers: 1. pollination by insects (or flood control, carbon storage)

24 Common misconceptions and links

Students often think…	Actually…
biodiversity means number of species	it includes ecosystem and genetic diversity, and evenness
extinction only happened in the past	current rates are far above background rates
zoos alone can save species	ex situ conservation works best alongside protection of habitats
more species always means a healthier ecosystem	evenness and native species matter too

How A4.2 connects to the rest of the course

Topic	Connection
A3.1 Diversity	species and genetic variation
C4.1 Populations and communities	keystone species, competition, predation
D4.2 Sustainability	sustainable use of resources
D4.3 Climate change	climate threats to species
A4.1 Speciation	how biodiversity arises

25 Exam-style question with markscheme

Try this under exam conditions (about 15 minutes) before reading the markscheme.

Figure 2. Rainforest cover in a region of Borneo.

Text A. Rainforest in the region has been cleared mainly for oil palm plantations. Orangutan numbers have halved. A new wildlife corridor connecting two reserves is planned, and a zoo programme breeds orangutans in captivity.

(a) Calculate the percentage loss of rainforest between 2000 and 2020. [1]

(b) Explain how habitat loss threatens orangutans. [3]

(d) Explain how a wildlife corridor could help conserve the population. [2]

Markscheme

Part	Answer	Marks
(a)	34%	A1
(b)	loss of food and shelter	R1
	fragmentation into small isolated populations	R1
	loss of genetic diversity / inbreeding	R1
(c)	maintains a reserve population; education	R1 R1
	low genetic diversity; loss of behaviour; reintroduction fails if habitat lost	R1 R1
(d)	connects fragments, allowing movement	R1
	gene flow between populations; larger effective population	R1

Examiner's comments. In (c), the best answers argued that captive breeding cannot succeed without protecting habitat.

26 Check your understanding

Section A: multiple choice

1. Genetic diversity is

A. the variety of alleles within a species B. the number of species C. the number of habitats D. the size of a population

2. A mass extinction involves loss of at least

A. 10% of species B. 25% of species C. 75% of species D. all species

3. The largest current cause of biodiversity loss is

A. volcanoes B. habitat loss C. asteroids D. natural selection

4. A seed bank is an example of

A. in situ conservation B. rewilding C. habitat restoration D. ex situ conservation

5. EDGE species are

A. the most common species B. evolutionarily distinct and globally endangered C. invasive species D. domestic species

6. Species evenness describes

A. how evenly individuals are spread among species B. the number of species C. genetic diversity D. habitat area

Section B: structured

7. Distinguish the three levels of biodiversity. [3]

8. Explain three causes of biodiversity loss with examples. [6]

9. Compare in situ and ex situ conservation. [4]

10. Calculate Simpson's reciprocal index for 8, 8 and 4 individuals of three species. [2]

Answers

1. A 2. C 3. B 4. D 5. B 6. A

7. Ecosystem: variety of habitats; species: richness and evenness; genetic: allele variety.

8. Habitat loss (oil palm), overexploitation (cod), invasive species (rats in New Zealand).

9. In situ: natural habitat, whole ecosystems; ex situ: zoos, seed banks, rescue; strengths and weaknesses.

10. N = 20; Σn(n−1) = 56 + 56 + 12 = 124; D = 380 ÷ 124 = 3.06.

27 Summary and topic map

Idea	Remember
Biodiversity	ecosystem, species, genetic
Measuring	surveys, eDNA; Simpson's index
Mass extinctions	five in the past; sixth under way
Causes	habitat loss, overexploitation, invasive species, pollution, climate change
In situ	reserves, corridors, rewilding
Ex situ	zoos, seed banks, captive breeding
Priorities	hotspots, EDGE, flagship, keystone

Before the exam, make sure you…

•name the three levels of biodiversity
•give a named example for each cause
•evaluate conservation methods both ways
•calculate Simpson's index step by step

Conservation of Biodiversity on one page

Cover this page with a sheet of paper and try to rebuild it from memory. Whatever you can't recall is what to revise next.

Figure 3. Topic map for Conservation of Biodiversity.

revisionprep.comIB-style notes · question bank · mock papers