How Many Different Species Of Animals Are There In The World

Humans brand upwardly just 0.01% of Earth's life – what'southward the balance?

Our planet is home to an incredible diversity of organisms. What does Globe'due south biodiversity await similar in the big moving picture?

In this post I provide an overview – with summary graphic – of Earth's biomass, how information technology is distributed between taxa (the taxonomic grouping of organisms), and the environments within which they live. This summary is based on the findings of research by Bar-On, Phillips & Milo published in theProceedings of the National University of Sciences (PNAS).^one

Humans account for simply 0.01% of biomass

There are several ways we can reply the question of how much life is on Earth. We could, for instance, count the number of species, population sizes or the number of individual organisms. But these metrics can make information technology difficult to compare betwixt taxa: minor organisms may accept a large population just however account for a very pocket-sized per centum of World's organic matter.

For a meaningful comparing, Bar-On et al. (2018) quantified life using the metric of biomass. Biomass is measured here in tonnes of carbon as it is a key building-block of life.^two

In the graphic below I summarize the distribution of global biomass by taxonomic kingdom (on the left), with a magnified snapshot of the animate being kingdom (on the right).

What are the stand-out points?

plants – mainly trees – dominate life on Earth: they account for more than than 82% of biomass;
surprisingly in second place is the life we cannot run into: tiny bacteria sum up to 13%;
whilst our perceptions are often focused on the animal kingdom, it accounts for only 0.4%;
humans account for just 0.01% of biomass, so we'd need nigh 70 trillion of u.s.a. to friction match Earth's collective biomass.³

Livestock outweighs wild mammals and birds ten-fold

Humans incorporate a very small share of life on Earth — 0.01% of the total, and 2.v% of fauna biomass [animal biomass is shown in the right-paw box on the visualization higher up].

Simply nosotros are likewise responsible for the animals we raise. Humans lonely may seem insignificant, but our hunger for raising livestock means we take played a major function in shifting the residual of animal life: livestock business relationship for 4% of brute biomass.⁴

Livestock accounts for more biomass than all humans on Earth; more than 50% greater than humans.

And livestock accounts for much more than all wildlife: Wild mammals and birds collectively business relationship for simply 0.38% — livestock therefore outweighs wild mammals and birds by a cistron of ten.^five

Oceans, land and deep subsurface: how is life distributed across environments?

The visualization here provides a snapshot of how life spans beyond the planet'due south environments. This summary is based on the findings of research by Bar-On, Phillips & Milo published in theProceedings of the National Academy of Sciences (PNAS).⁶

There are three high-level habitat environments: state, marine, and deep subsurface environments. Deep subsurface environments can be terrestrial or below the sea floor, but represent habitats deep beneath the surface – extending from around 50 metres to thousands of metres below the surface.⁷

Most of life exists on country — 86% of biomass. This is because almost all plant life – by and large trees – is terrestrial. The authors guess that marine plants, for example seaweed, make up less than ane billion tonnes of carbon. This is less than 0.2% of total plant biomass.^eight Most bacteria and archaea exists in the deep subsurface, meaning 13 percent of global biomass thrives in this surroundings.

Despite dominating our planet in terms of area and book – taking upwards more than 70% of global surface expanse – the oceans are home to just 1% of biomass. But they do dominate the beast kingdom: 78% of fauna biomass lives in the marine environment.

With lifeforms ranging in size from the microscopic cellular level to large lifeforms that bridge tens of hectares,⁹ it is impossible to contextualize life on Earth through experience or intuition lone.

Just expect at the viruses that live in the bounding main: while each ane of them is tiny, if we placed all the viruses finish-to-end they would stretch for x million light years. That is around 100 times the altitude across our own galaxy.^x On state the scale is just as mindblowing: there are more 10¹⁶ prokaryotes in a ton of Earth's soil – orders of magnitude more the 'mere' 10^eleven stars in our galaxy.^xi

Looking at the big numbers allows u.s. to empathize our planet and our place in it.

How many species are there?

How many species accept nosotros described?

Before we look at estimates of how many species at that place are in total, nosotros should also enquire the question of how many species nosotros know that we know. Species that we have identified and named. This is only a fraction of the bodily number of species on Earth considering there are so many that we oasis't nevertheless plant or studied.

The IUCN Red Listing tracks the number of described species and updates this figure annually based on the latest work of taxonomists. In 2021 it listed two.13 million species on the planet. In the chart nosotros see the breakdown across a range of taxonomic groups – i.05 one thousand thousand insects; over eleven,000 birds; over eleven,000 reptiles; and over 6,000 mammals.

These figures – specially for lesser-known groups such as plants or fungi – might be a flake too high. This is because some described species end up being synonyms – the description of already-known species, simply given a separate proper noun.¹² At that place is a continual evaluation process to remove synonyms (and virtually are removed eventually), just often species are added at a faster rate than synonyms can exist institute and removed.^xiii To give a sense of how big this effect might be, in a study published in Science, Costello et al. (2013) estimated that effectually twenty% of the described species were undiscovered synonyms (in other words, duplicates).¹⁴ They estimated that the 1.ix 1000000 described species at the fourth dimension was actually closer to 1.5 million unique species.

If nosotros were to presume this "xx% synonym" figure held true, our 2.12 meg described species might actually be closer to one.7 meg.

Regardless, we know that any of these figures are an underestimate of the actual number of species. The fact that there are then many species that we've yet to discover has existent consequences for our ability to empathise changes in global biodiversity and the charge per unit of species extinctions. If we don't know that certain species exist, nosotros also don't know that they might have, or will soon, go extinct. Some species will inevitably go extinct earlier nosotros realise that they existed.

How many species are there actually?

How many species do we share our planet with? Information technology'southward such a bones and primal question to understanding the globe around us. It's almost unthinkable that we would non know, or at least accept a good estimate, what this number is. Merely the truth is that it's a question that continues to escape the world'south taxonomists.

As Robert May summarised in a paper published in Science ¹⁵:

If some alien version of the Starship Enterprise visited Earth, what might be the visitors' kickoff question? I think it would be: "How many distinct life forms—species—does your planet accept?" Embarrassingly, our best-gauge answer would be in the range of 5 to ten million eukaryotes (never heed the viruses and bacteria), but we could defend numbers exceeding 100 million, or as depression every bit 3 meg.

Over decades, researchers have made a number of broad-ranging estimates. Equally May points out, this ranges anywhere from 3 to 100 million – 2 orders of magnitude of divergence. Nearly modern estimates autumn inside a tighter range.

One of the most widely-cited figures comes from Camila Mora and colleagues; they estimated that there were around 8.7 1000000 species on World today. ¹⁶ Mora et al. put an uncertainty of 1.iii million species effectually this figure. The breakup of how many of these species are animals; fungi; plants; and other groups is shown in the table. This as well shows the carve up between marine and terrestrial environments. It's estimated that two.2 million of these species lived in the bounding main.

There are also a range of other estimates: Costello et al. (2013) estimate v ± 3 million species; Chapman (2009) estimates eleven meg; and after reviewing the range in the literature, Scheffers et al. (2012) cull non to requite a physical effigy at all.¹⁷ There is typically strong agreement on the well-nigh well-studied taxonomic groups such as mammals, birds, and reptiles. Where most of the disagreement lies is in insects, fungi, and other smaller microbial species. Reaching consensus on such small and inaccessible lifeforms is undoubtedly difficult.

How tin can nosotros even begin to make these estimates? There are several approaches that researchers take.

Mora et al. (2011) – whose estimates are shown in the table – used the fact that there are anticipated relationships in higher taxonomic classifications of life, that could be extrapolated to the species level. Life can exist classified at multiple levels: each belongs to a kingdom (e.g. the "Animalia" kingdom – this sorts life into animals, plants, fungi etc.); then a phyla (eastward.g. "Mollusca" or "Arthropoda" in the animal kingdom); then class; gild; family; genus; and finally the species level. We know much more nigh the college taxonomic classifications (kingdoms, phylum; classes) than we do nigh the specific species-level breakdowns. Merely, we find that for groups of species that take been well-studied, we notice predictable patterns between the higher taxonomic classifications, and estimates at the species-level. Researchers can utilise these anticipated patterns for well-known species and apply them to lesser-known groups.

The honest answer to the question, "how many species are in that location?" is that we don't actually know. Some estimates span several orders of magnitude, from a few to 100 million. But virtually recent estimates lie somewhere in the range of effectually v to x meg.

Kingdom	Number of species (Ocean)	Number of species (Terrestrial)	Number of species (Total)
Animals	two,150,000	5,620,000	vii,770,000
Chromists	7400	20,100	27,500
Fungi	5320	605,680	611,000
Plants	sixteen,600	281,400	298,000
Protozoa	36,400	0	36,400
Archaea	1	454	455
Bacteria	1320	8360	9680
Full species	two,210,000	6,540,000	8,750,000

Estimated number of species on Earth from Mora et al. (2011)¹⁸

Biodiversity across the world

The earth is home to millions of species, each adjusted to different environments: tropical, temperate, polar; terrestrial; freshwater or marine; high or low altitude; dry; moisture or a mixture of both. Most places on Earth are domicile to at to the lowest degree some unique species, but the density of biodiversity varies a lot across the world'southward continents.

The following maps evidence the density of endemic species by country across a range of taxonomic groups. Endemic species are those that naturally occur in only one geographical locations. In other words, they are unique to that place.

What we see is that the tropics is incredibly dense in unique wildlife. In nearly every map we see a bright belt along the equator – this is true of mammals, birds, coral reefs, amphibians and a range of fish species. It's estimated that tropical forests alone are home to more than one-half of the planet's species.¹⁹ This is of import considering, unfortunately, this also where the greatest threats to wildlife exist today. It's where 95% of deforestation occurs, and where the most mammals, birds, amphibians and reptiles are hunted and poached. If we want to protect these species nosotros need to first empathize where they alive; what the pressures are; and what we can practice about it.