Biodiversity · Taxonomy
About 8.7 million species — and roughly seven in eight have never been described
Save this development or follow its topic to track what changes.
Short answer
A higher-taxon extrapolation estimates ~8.7 million eukaryotic species, of which roughly 14% on land and 9% in the ocean are described.
What happened
Mora, Tittensor, Adl, Simpson and Worm used the fact that higher taxa (phyla, classes, orders) are discovered and then saturate long before species do. Fitting that pattern and extrapolating gives ~8.7 million eukaryotic species on Earth and ~2.2 million in the ocean. Validation against well-sampled groups supported the approach. A parallel survey drew responses from 548 of about 2,938 contacted taxonomists on synonymy and effort.
Why it matters
The headline is not the number but the fraction: on this estimate only about 14% of terrestrial and 9% of marine eukaryotic species have been catalogued after 250 years of taxonomy. That sets the scale of what biodiversity loss statistics are actually measuring.
Evidence
- Study type
- Higher-taxon extrapolation model validated against well-sampled groups, with a taxonomist survey
- Sample
- Global taxonomic catalogues; 548 of ~2,938 contacted taxonomists responded (18.7%)
- Journal
- PLoS Biology · peer reviewed
- Replication
- The approach has been re-run and contested by later estimates; the order of magnitude is more durable than the exact figure
- Limitations
- A model, not a census. Prokaryotes are excluded because the species concept does not transfer. Unresolved synonyms bias the catalogued baseline.
What this connects to
Sources
The 2 studies this explanation is built from, by the role each plays. Every source links to PaperFren’s explanation of it and to the original paper.
Primary study
- How many species live on Earth and in the ocean?
A validated taxonomic extrapolation estimates ~8.7 million eukaryotic species on Earth, with most still undescribed.
What it does not showLimitations
Prokaryote diversity is poorly captured by the same species concept; estimates will shift with better synonym control and sampling.
PaperFren explanationStudy with cards and a quizOriginal paper (DOI)cc by
Supporting evidence
- How will climate and land use hit bird diversity?
Integrating climate and land-use change via land-cover exposure projects substantial impacts on global bird diversity, with clear ecological assumptions.
What it does not showLimitations
Assumes persistent habitat associations and limited dispersal; finer habitat specialization may be missed by coarse land-cover classes.
PaperFren explanationStudy with cards and a quizOriginal paper (DOI)cc by
Before
Published expert estimates of global species richness spanned more than an order of magnitude, from about 3 million to 100 million, with no shared method to choose between them.
Now
A method with an internal validity check narrows the range considerably. It is still a model extrapolation, it does not cover prokaryotes — whose species concept differs — and it will move as synonymy and sampling improve.