IB ESS HL3.1 Biodiversity & EvolutionHL only~11 min read
What Makes a Biodiversity Hotspot
The Amazon is not a biodiversity hotspot. That sounds wrong, and it is the single most useful thing on this page — because the reason why reveals what the term actually measures, and it is not just “lots of species”.
📘 What you need to know
Biodiversity hotspots contain large numbers of species that are rare, endemic and endangered.
Two criteria must both be met: at least 1 500 endemic vascular plant species, and loss of at least 70% of original natural vegetation.
The criteria were developed by Norman Myers and are used by Conservation International.
The Amazon does not qualify, because it has not reached the 70% habitat-loss threshold.
Hotspots cover less than 3% of Earth’s surface but hold more than half of the world’s plant species.
Biodiversity is unevenly distributed: low at the poles, very high in tropical rainforests.
Tropical biomes lie roughly between 15° north and 15° south and cover about 6% of Earth’s surface.
What a hotspot is
Biodiversity hotspots are areas on Earth containing a large number of different species, particularly those that are rare, endemic (found only in that area) and endangered. They are critical for conservation because they often hold species found nowhere else — and they are also among the regions most under threat from human activities such as deforestation, pollution and habitat destruction.
The two criteria
Criteria developed by ecologist Norman Myers and used by Conservation International. They target places that are both irreplaceable and in immediate danger.
To qualify as a biodiversity hotspot, an area must meet two criteria:
High endemism. The area must contain at least 1 500 species of vascular plants that are endemic.
Significant habitat loss. The area must have lost at least 70% of its original natural vegetation, indicating that the region is under severe threat from human activities and in urgent need of conservation.
These criteria were developed by ecologist Norman Myers and are used by Conservation International. They deliberately focus on areas of both high biodiversity and critical levels of habitat loss.
The Amazon exception. The Amazon rainforest does not currently qualify as a biodiversity hotspot, because it has not yet met the second criterion. It faces significant deforestation and other threats, but has not reached the 70% threshold of habitat destruction — though deforestation rates are increasing. Students describe the Amazon as a hotspot constantly, and it is a reliable way to lose a mark.
Biodiversity is unevenly distributed
Hotspots also hold a large percentage of the world’s animal species. The area-to-species mismatch is the whole argument for prioritising them.
Biodiversity is not evenly spread across the planet. The poles have low biodiversity; tropical rainforests have very high biodiversity. Hotspots make up less than 3% of Earth’s surface but contain more than half of the world’s plant species and a large percentage of its animal species. They are often located in areas with unique climates and geographical features that allowed species to evolve and adapt to specific niches.
Hotspots in tropical biomes
Many hotspots are in tropical biomes, which tend to have the highest levels of biodiversity. The warm, wet conditions of a tropical rainforest support a wide range of plants, insects, birds and mammals.
Tropical hotspot
What makes it exceptional
The Coral Triangle, Southeast Asia
Home to more than 600 species of reef-building corals
Madagascar
Over 90% of its species are endemic
Tropical biomes lie mainly in a band between 15° north and 15° south of the equator, within the equatorial climate zone. Covering only about 6% of Earth’s surface, the main tropical regions are:
Region
Countries
Amazon
The largest remaining rainforest on Earth, usually associated with Brazil but covering parts of seven other South American countries
Central America
Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua and Panama
Central Africa
Cameroon, Central African Republic, Republic of Congo, Democratic Republic of Congo, Equatorial Guinea and Gabon
Indo-Malaysia
Malaysia, Indonesia and other countries in South-East Asia
There is a genuine tension in the hotspot concept worth noticing. Because criterion 2 requires 70% habitat loss, a region only becomes a designated hotspot after most of it has already been destroyed. That directs funding towards the most urgent cases, but it also means an intact, highly diverse region like the Amazon receives no hotspot status until it has been badly damaged. If a question asks you to evaluate the concept, that is the strongest point you can make.
Worked examples
WE 1
The two criteria
State the two criteria an area must meet to be classified as a biodiversity hotspot. (2 marks)
Criterion 1
The area must contain at least 1 500 species of endemic vascular plants, meaning species found nowhere else.
Criterion 2
The area must have lost at least 70% of its original natural vegetation, showing it is under severe threat and in urgent need of conservation.
1 500 endemic plant species, and 70% habitat already lostboth figures are required — a vague answer scores nothing here
WE 2
The Amazon question
Explain why the Amazon rainforest is not classified as a biodiversity hotspot. (3 marks)
Step 1: both criteria are needed
An area must meet both criteria: at least 1 500 endemic vascular plant species, and at least 70% loss of original natural vegetation.
Step 2: which one it fails
The Amazon comfortably satisfies the endemism criterion, but it has not yet reached the 70% threshold of habitat destruction.
Step 3: the trend
It does face significant deforestation and other threats, and deforestation rates are increasing, so this may change.
High biodiversity, but not yet enough habitat loss to qualifythis is the most commonly examined misconception in the sub-topic
Reason 1: efficiency
Hotspots cover less than 3% of Earth’s surface but contain more than half of the world’s plant species and a large percentage of its animal species, so protecting a small area protects a great deal of biodiversity.
Reason 2: irreplaceability
They contain large numbers of endemic species found nowhere else, so if those areas are lost the species are lost globally.
Reason 3: urgency
By definition they have already lost at least 70% of their original vegetation, so they are under severe and immediate threat.
Maximum biodiversity protected per unit of area, in the places most at riskthe 3% versus half-the-plant-species contrast is the strongest single point
💡 Exam tips
Learn both figures exactly: 1 500 endemic vascular plants and 70% habitat loss.
Stress that both criteria must be met.
Know the Amazon exception and why it applies.
Quote the mismatch: under 3% of land, over half of plant species.
Have two tropical examples ready: the Coral Triangle and Madagascar.
Credit Norman Myers and Conservation International for the criteria.
⚠ Common mistakes
Calling the Amazon a hotspot. It fails the habitat-loss criterion.
Giving only one criterion. Both are required, and both carry marks.
Saying hotspots are simply areas of high biodiversity. Threat level is half the definition.
Confusing endemic with rare. Endemic means restricted to one area.
Forgetting the criterion specifies vascular plants. Not all species.
Assuming all hotspots are tropical. Many are, but it is not part of the definition.
Up next: How Humans Redirect Evolution. Hotspots exist because human activity destroys habitat. The next page shows that we do not only remove species — we change the direction in which the survivors evolve.
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