IB ESS SL3.2 Human Impact on BiodiversityPaper 1 & 2Core skill~12 min read
Judging Conservation Status
Conservation money and attention are limited, so someone has to decide which species need help first. That decision cannot be a hunch. The IUCN turns it into an assessment with defined categories, so a frog in Peru and a fern in Wales can be compared on the same scale.
📚 What you need to know
International cooperation is essential for conservation, and several agreements and authorities exist to deliver it.
The IUCN is the global authority on the status of the natural world and what is needed to safeguard it.
It assesses the conservation status of species using data and modelling.
Many factors feed in: population size and trend, geographic range, specialisation, breeding potential, habitat quality and fragmentation, trophic level and known threats.
The categories are LC, NT, VU, EN, CR, EW, EX, plus DD (data deficient) and NE (not evaluated).
Assessments are published in the IUCN Red List of Threatened Species, which is public.
Fewer than 5% of the world’s described species have been assessed, so the picture is far from complete.
Why status assessment exists
Species do not respect borders, so conservation only works with international cooperation. Several agreements and authorities operate within and between countries with the aim of protecting species worldwide.
The International Union for the Conservation of Nature (IUCN) is the recognised global authority. One of its main duties is assessing the conservation status of animal and plant species around the world. Scientists use data and modelling to estimate which category each species belongs in.
The categories
The three middle-to-right categories — VU, EN and CR — are together called “threatened”. If a question uses that word, it means those three.
Code
Category
What it means
LC
Least concern
Assessed and found not to be at risk at present
NT
Near threatened
Close to qualifying as threatened, or likely to soon
VU
Vulnerable
Facing a high risk of extinction in the wild
EN
Endangered
Facing a very high risk of extinction in the wild
CR
Critically endangered
Facing an extremely high risk of extinction in the wild
EW
Extinct in the wild
Survives only in captivity or outside its natural range
EX
Extinct
No individuals remain
DD
Data deficient
Not enough information to place it in a category
NE
Not evaluated
Has not yet been assessed against the criteria
🧠
Easy way to remember the order
Little Need to Very Extremely Concerned, then Extinct in the Wild, then EXtinct. Or just remember the risk rises steadily left to right and the last two are the end of the line.
What the assessment actually looks at
It is not simply a headcount. The IUCN weighs a long list of factors, and a species can be in trouble even with reasonably large numbers.
Read the two columns across, one row at a time. Each pair is the same question asked of two different species.
Factor
Why it matters
Population size
Smaller populations are at greater risk, and also lose genetic diversity faster
Rate of increase or decrease
A large population falling steeply can be in more trouble than a small stable one
Degree of specialisation
A specialist with one food source or one habitat type cannot switch when things change
Geographic range and distribution
A wide range spreads the risk; a narrow one means a single event can hit everything
Degree of endemicity
A species found in only one specific area has nowhere else to survive
Reproductive potential and behaviour
Slow breeders recover slowly, so a decline takes far longer to reverse
Habitat fragmentation and quality
Fragmented, degraded habitat isolates populations and reduces what they can support
Trophic level
Animals at higher trophic levels have smaller populations and accumulate toxins
Known threats
Active hunting, invasive species or planned development all raise the assessed risk
The factor students underuse is endemicity. A species found on one island has no escape route: one fire, one introduced rat, one storm, and the whole species is gone. If a question describes a species restricted to a single location, that word belongs in your answer.
What the Red List is for, and what it cannot do
Assessments are published in the IUCN Red List of Threatened Species, which is freely available online.
Giving a species a global conservation status highlights how vulnerable it is in a way anyone can understand.
This helps governments, NGOs and individuals choose conservation priorities and appropriate management strategies.
Because every assessment uses the same criteria, species and regions can be compared directly.
Scientists continually update and review the list as new data arrives, so a status can improve as well as worsen.
The coverage problem. The number of species assessed rises every year — by 2023 it had reached nearly 160 000, roughly double the figure from 2016. That still means extinction risk has been evaluated for less than 5% of the world’s described species, and described species are themselves only a fraction of the species thought to exist. Most of what is at risk has never been looked at.
Assessment is biased towards large, charismatic and well-studied groups. Mammals and birds are well covered; insects, fungi and soil organisms are barely covered at all.
Data deficient is not the same as safe. It means nobody knows, and DD species may well be threatened.
Status is a global judgement. A species can be least concern worldwide and locally extinct in your country.
Worked examples
WE 1
Outline how conservation status is assessed
Outline the role of the IUCN in assessing conservation status. (3 marks)
Point 1: the body
The IUCN is the global authority on the status of the natural world and the measures needed to safeguard it.
Point 2: the method
It uses data and modelling to place species into categories from least concern through to extinct, based on factors such as population size, trend, range and known threats.
Point 3: the purpose
Results are published in the public Red List, helping governments, NGOs and individuals set conservation priorities.
One global scale, so effort can go where the risk is highestname at least three assessment factors; a list of categories alone is only worth one mark
WE 2
Apply the criteria to a species
A bird lives only on one small island, feeds on a single species of fruit, lays one egg every two years, and its population has fallen by half in ten years. Suggest why it would be assessed as critically endangered. (4 marks)
Point 1: endemicity and range
It is endemic to one small island, so its geographic range is tiny and a single event could affect the whole species.
Point 2: specialisation
Feeding on one fruit species makes it a specialist, so it cannot switch food if that plant declines.
Point 3: reproductive potential
One egg every two years is very low breeding potential, so the population recovers extremely slowly.
Point 4: rate of decline
A 50% fall in ten years is a steep rate of decrease, indicating the threats are active now.
Tiny range, specialist diet, slow breeder, falling fast — every factor points the same waywork through the factors the question gives you one at a time; each is a mark
WE 3
Evaluate the Red List
Evaluate the usefulness of the IUCN Red List as a conservation tool. (4 marks)
Strength 1
It applies the same criteria worldwide, so species and regions can be compared and effort directed to the highest risk.
Strength 2
It is public and regularly updated, so governments, NGOs and the public can all act on the same evidence.
Limitation 1
Fewer than 5% of described species have been assessed, and coverage is biased towards large, well-studied groups.
Limitation 2
Assessments depend on data quality; many species are listed as data deficient, and status is global so it can hide local extinctions.
Judgement
An essential tool for setting priorities, but an incomplete picture that should not be read as a full account of what is at risk.
The best list we have, covering a small slice of life on Earththe coverage statistic is the single most useful fact to quote in this question
💡 Exam tips
Learn the seven categories in order, plus DD and NE.
Know that threatened covers VU, EN and CR.
Learn at least five assessment factors, and use the ones the question gives you.
Use the terms endemic, specialisation and reproductive potential — they are high-value.
Quote the under 5% assessed figure in any evaluation of the Red List.
Remember data deficient means unknown, not safe.
⚠ Common mistakes
Judging status on population size alone. Range, trend and specialisation matter just as much.
Confusing extinct with extinct in the wild. EW species still survive in captivity.
Treating data deficient as least concern. It means nobody has enough information.
Thinking the IUCN is a government body. It is an international conservation organisation.
Assuming the Red List covers everything. Most described species have never been assessed.
Ignoring that status changes. The list is reviewed continually, in both directions.
Up next: Case Studies in Decline and Recovery — the categories become real when you follow individual species down the scale, and occasionally back up it.
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