IB ESS SL & HL3.2 Human Impact on BiodiversityPaper 1 & 2~11 min read
Judging Conservation Status
The IUCN Red List is the closest thing conservation has to a global scoreboard. It has assessed around 160 000 species — which sounds enormous until you realise that is under 5% of the species we have actually described.
📘 What you need to know
International cooperation is essential for successful conservation.
The IUCN is the global authority on the status of the natural world and the measures needed to safeguard it.
Scientists use data and modelling to estimate which category a species belongs in.
Factors include population size, rate of change, degree of specialisation, distribution, reproductive potential, endemicity, habitat fragmentation, habitat quality, trophic level and known threats.
Seven main categories run from LC to EX, plus DD (data deficient) and NE (not evaluated).
The Red List is public, helping governments, NGOs and individuals set conservation priorities.
By 2023 just under 160 000 species had been assessed — still less than 5% of described species.
Who does the assessing
International cooperation is essential if conservation is to succeed, and several agreements and authorities exist within and between countries to protect species worldwide. The International Union for the Conservation of Nature (IUCN) is the global authority on the status of the natural world and the measures needed to safeguard it.
One of its 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 should be placed in.
The categories
Note the difference between EW and EX. A species extinct in the wild may still survive in captivity, which is why captive breeding matters.
Species that have been assessed are categorised as:
Code
Category
LC
least concern
NT
near threatened
VU
vulnerable
EN
endangered
CR
critically endangered
EW
extinct in the wild
EX
extinct
Species can also be classed as DD (data deficient) when there is not enough data on which to base a category choice, or NE (not evaluated).
What the assessment looks at
Grouping the ten factors this way makes them far easier to recall than a flat list, and shows why population size alone is not enough.
Factors used to determine conservation status include:
Population size — smaller populations are usually at greater risk of extinction.
Rate of increase or decrease of the population.
Degree of specialisation.
Distribution and geographic range.
Reproductive potential and behaviour — breeding potential.
Degree of endemicity — whether the species is found only in one specific area.
Degree of habitat fragmentation and quality of habitat.
Trophic level — animals at higher trophic levels are usually at greater risk.
Known threats.
The Red List, and what it does not cover
Species on the IUCN Red List of Threatened Species can be viewed online, as the list is made public. Giving a global conservation status highlights how vulnerable certain species are, helping governments, NGOs and individuals select appropriate conservation priorities and management strategies.
The number of species assessed increases every year. By 2023 the figure reached just under 160 000 species — roughly double the number assessed in 2016. Even so, extinction risk has been evaluated for less than 5% of the world’s described species.
Why the 5% figure matters. It means the Red List is a sample, not a census — and it is not a random sample. Large, charismatic vertebrates are far better assessed than insects, fungi or plants. A species can only be listed as threatened once someone has looked, which is exactly why the DD category exists and why “not listed as threatened” is very different from “not threatened”.
The assessment factors are worth grouping rather than memorising as a list. Ask three questions about any species: how many are there and which way is the number moving; how widely spread are they; and how fussy are they about where and what they live on. That covers nine of the ten factors, and “known threats” is the tenth.
Worked examples
WE 1
The categories
List the IUCN categories in order of increasing extinction risk. (2 marks)
The seven assessed categoriesLeast concern (LC), near threatened (NT), vulnerable (VU), endangered (EN), critically endangered (CR), extinct in the wild (EW), extinct (EX).
The two additional codes
Species may also be classed as data deficient (DD) when there is not enough data to choose a category, or not evaluated (NE).
LC, NT, VU, EN, CR, EW, EX — plus DD and NE outside the scalegive both the code and the full name to be safe
WE 2
Assessing status
Explain why population size alone is not sufficient to determine a species’ conservation status. (4 marks)
Point 1: direction matters
The rate of increase or decrease is as important as the number. A large but rapidly falling population may be at greater risk than a small stable one.
Point 2: range matters
Distribution, geographic range and degree of endemicity all affect risk. A species found in only one place can be wiped out by a single local event.
Point 3: ecology matters
Degree of specialisation, habitat quality, habitat fragmentation and trophic level all influence vulnerability. Animals at higher trophic levels are usually at greater risk.
Point 4: threats matter
Known threats and reproductive potential determine whether a population can recover from losses.
Numbers say where a species is; the other factors say where it is headinggrouping the factors shows understanding rather than memorisation
WE 3
Limits of the Red List
Evaluate the usefulness of the IUCN Red List. (4 marks)
Strength 1: a shared global standard
The IUCN is the global authority on the status of the natural world, and assessments use data and modelling applied consistently across species.
Strength 2: it drives action
The list is public, so giving a global conservation status highlights how vulnerable species are and helps governments, NGOs and individuals set conservation priorities and management strategies.
Limitation 1: coverage
Despite nearly 160 000 species assessed by 2023, extinction risk has been evaluated for less than 5% of described species.
Limitation 2: data quality
Some species are classed as data deficient because there is not enough information to assign a category, so absence from the threatened list does not mean a species is safe.
Authoritative and actionable, but covering only a small fraction of lifethe under-5% figure is the single most useful statistic here
💡 Exam tips
Know all seven categories in order, plus DD and NE.
Learn what IUCN stands for and that it is the global authority.
Quote the coverage figures: almost 160 000 assessed by 2023, under 5% of described species.
Give several assessment factors, not just population size.
Remember higher trophic level means higher risk.
Distinguish EW from EX: extinct in the wild still exists in captivity.
⚠ Common mistakes
Muddling the category order. Vulnerable comes before endangered, not after.
Treating DD as a low-risk category. It means we do not know.
Saying the Red List covers all species. Under 5% have been evaluated.
Giving only population size as a factor. There are around ten.
Confusing the IUCN with the WWF. The Red List belongs to the IUCN.
Assuming a status is permanent. Scientists continually update and review them.
Up next: Case Studies in Decline and Recovery. The categories are abstract until you attach species to them — two that were lost, two clinging on, and two that came back.
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