IB Biology HLProtecting BiodiversityPaper 1 & 2~13 min read
Loss of Biodiversity
Claiming that biodiversity is falling is easy. Proving it takes millions of records, from thousands of habitats, gathered over decades. This page covers where that evidence comes from, and what is actually driving the loss.
📚 What you need to know
Trustworthy evidence needs many reliable surveys across a wide range of habitats, repeated over time, assessing both richness and evenness, and expertly analysed.
Citizen scientists are members of the public who help gather data, increasing the quantity but sometimes reducing the quality.
IPBES gathers information, recommends policies and communicates findings; its 2019 report summarised research and made policy recommendations.
The IUCN maintains the red list of threatened species: over 150 000 species assessed, over 42 000 listed as threatened.
Red list categories: LC, NT, VU, EN, CR, EW, EX, plus DD (data deficient) and NE (not evaluated).
The main underlying cause of the crisis is growth of the global human population — now more than 8 billion and still rising.
Direct causes: overexploitation, urbanisation, deforestation and habitat loss, pollution, pests, invasive species and disease.
The evidence for biodiversity loss
To understand the nature and extent of the biodiversity crisis, solid evidence on the world’s changing biodiversity is required. For that evidence to be trustworthy it needs to contain enough data and come from reliable sources.
Requirement
Why it matters
Many reliable biodiversity surveys in a wide range of habitats
One habitat cannot represent the whole planet
Repeat survey data over a period of time
A single snapshot cannot show a trend
Both species richness and species evenness assessed
Numbers can fall long before any species disappears
Data expertly analysed
Raw records mean nothing until they are analysed properly
Drawing together evidence on this scale is a huge task, and it is usually done by organisations that work across multiple governments.
IPBES
IPBES is the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. It works to gather information, recommend policies and communicate findings about global biodiversity and ecosystems.
The 2019 IPBES report contained a comprehensive summary of research findings, plus policy recommendations for governments.
Data is gathered by scientists, government bodies and local individuals.
Studies are carried out in a range of habitats where regular samples are taken.
IUCN and the red list
The IUCN is the International Union for the Conservation of Nature: a network of organisations and individual experts that gathers knowledge of the natural world and proposes environmental policies.
The IUCN red list is a list of the world’s most threatened species. It has assessed more than 150 000 species and listed more than 42 000 as threatened. It is compiled by scientists and scientific organisations worldwide, and is used by many groups to inform conservation efforts.
Learn the ladder in order. Questions often give you a category code and expect you to place it correctly on the scale.
NOS: evidence has to be verifiable
To be verifiable, evidence usually has to come from a published source that has been peer-reviewed, so that the methodology can be checked.
That creates a practical problem. Collecting data on global biodiversity is enormous, and even a large team of qualified scientists cannot cover changes at a national or international level. To solve it, organisations sometimes ask the public to help collect data. These people are called citizen scientists.
Using citizen scientists
What it does to the data
Far more people gathering records
Much greater quantity of data, over a much wider area
Volunteers are often untrained
Data may not always be valid, so quality can fall
Good experimental design and high-quality analysis
Mitigates the problem, e.g. simple standard methods and checks on submitted records
There is a genuine trade-off between the quality and the quantity of the data. That phrase is worth memorising, because a nature of science question here is really asking you to weigh two things against each other rather than pick a winner.
The causes of biodiversity loss
It is widely agreed among scientists that a biodiversity crisis is underway, because of the rate at which extinctions are occurring. The growth of the global human population is likely to be the main cause.
There are currently more than 8 billion people on Earth.
The global population continues to increase.
Even though birth rates are now decreasing, people are living longer, so births occur at a higher rate than deaths and the population keeps growing.
Learning the six spokes is far easier than learning a list, and it gives you a ready-made structure for any “explain the causes” question.
The causes in detail
Cause
What happens
Examples
Overexploitation
Resources are taken faster than populations can replace them
Overfishing causing a decline in fish populations; hunting for ivory from tusks, oil from whales, fur from beavers
Urbanisation
Building towns causes direct loss of habitat, and fragmentation of what is left into smaller pieces
Roads splitting habitats; less land left for farming, so agriculture expands elsewhere
Deforestation and habitat loss
Land is cleared and replaced with low-diversity systems
Clearing for agriculture, timber, mining and quarries; monocultures also cause loss of soil micro-organisms
Pollution
Harmful materials spread into habitats, including remote ones
Microplastics found in remote environments; fertilisers and organic waste washed off farmland into water
Pests
Biodiversity loss itself increases pest numbers, because there are fewer predators to control them
The cotton bollworm damaging crops; pests gathering in large numbers in monocultures
Invasive species
Humans moving around the world bring species with them, by accident or on purpose
Grey squirrels and signal crayfish in the UK, cane toads in Australia, rats in the Galapagos Islands
Disease
Pathogens can wipe out large numbers of species, and climate change extends their range
The chytrid fungus, thought to have wiped out about 90 species of amphibian; new diseases where humans live closely with animals
Watch the feedback loop. Pests are both a cause and a consequence. Losing biodiversity removes predators, pest numbers rise, farmers respond with pesticides and larger monocultures, and biodiversity falls further. Spotting that loop is worth a mark in an evaluation question.
Worked examples
WE 1
What makes the evidence trustworthy
Outline the features that biodiversity data must have to provide reliable evidence of biodiversity loss. (4 marks)
Point 1: coverage
Many reliable surveys are needed, carried out across a wide range of habitats.
Point 2: time
Surveys must be repeated over a period of time, because a single survey cannot show a change.
Point 3: what is measured
Both species richness and species evenness must be assessed.
Point 4: analysis and publication
Data must be expertly analysed and published in a peer-reviewed source so the methodology can be checked.
Wide coverage, repeated, both measures, expertly analysed“peer-reviewed” is the nature of science phrase and often carries its own mark
WE 2
Evaluating citizen science
Evaluate the use of citizen scientists in gathering biodiversity data. (3 marks)
Advantage
Members of the public greatly increase the quantity of data, allowing national and international coverage that scientists alone could not achieve.
Disadvantage
Citizen scientists are often untrained, so the data may not always be valid and quality may fall.
The judgement
There is a trade-off between quality and quantity, but good experimental design and high-quality analysis can reduce the problem.
More data, less certain data — manageable with good design“evaluate” needs both sides plus a conclusion; two advantages will not score full marks
WE 3
Invasive species
Explain how human travel has contributed to biodiversity loss. (3 marks)
Point 1: the mechanism
When humans travel they carry species with them, either accidentally or deliberately. These are invasive species.
Point 2: the effect
Native species have not evolved alongside them, so they may have no defences and are outcompeted or eaten.
Point 3: examples
Grey squirrels and signal crayfish in the UK, cane toads in Australia, and rats in the Galapagos Islands.
New arrivals, no evolved defences, native species declinegive at least one named example; a general statement rarely gets the third mark
💡 Exam tips
Know what IPBES and IUCN stand for and what each actually does.
Learn the red list categories in order, plus DD and NE.
Quote the IUCN figures: over 150 000 assessed, over 42 000 threatened.
Name human population growth as the underlying cause, then give specific direct causes.
Have one named example ready per cause — examiners reward specifics.
For citizen science, use the phrase trade-off between quality and quantity.
⚠ Common mistakes
Confusing IPBES and IUCN. IPBES advises on policy; IUCN maintains the red list.
Saying “endangered” for every threatened species. There are separate categories with separate meanings.
Mixing up EW and EX. Extinct in the wild means individuals still survive in captivity.
Listing causes with no examples. One named example per cause is what scores.
Saying birth rates rising causes population growth. Birth rates are falling; people living longer keeps births above deaths.
Treating citizen science as simply bad. It is a trade-off, and it can be managed.
Up next: Preserving Biodiversity — in situ and ex situ conservation, and how organisations decide which species to save first.
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