This is a collection of lists of organisms by their population. While most of the numbers are estimates, they have been made by the experts in their fields. Species population is a science falling under the purview of

population ecology Population ecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact with the environment, such as birth and death rates, and by immigration and emigration. The discipline is importa ...

and

biogeography Biogeography is the study of the distribution of species and ecosystems in geographic space and through geological time. Organisms and biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, ...

. Individuals are counted by census, as carried out for the

piping plover The piping plover (''Charadrius melodus'') is a small sand-colored, sparrow-sized shorebird that nests and feeds along coastal sand and gravel beaches in North America. The adult has yellow-orange-red legs, a black band across the forehead from e ...

; using the

transect method A transect is a path along which one counts and records occurrences of the objects of study (e.g. plants). There are several types of transect. Some are more effective than others. It requires an observer to move along a fixed path and to count ...

, as done for the

mountain plover The mountain plover (''Charadrius montanus'') is a medium-sized ground bird in the plover family (Charadriidae). It is misnamed, as it lives on level land. Unlike most plovers, it is usually not found near bodies of water or even on wet soil; i ...

; and beginning in 2012 by satellite, with the

emperor penguin The emperor penguin (''Aptenodytes forsteri'') is the tallest and heaviest of all living penguin species and is endemic to Antarctica. The male and female are similar in plumage and size, reaching in length and weighing from . Feathers of th ...

being first subject counted in this manner.

Number of species

More than 99 percent of all species, amounting to over five billion species, that ever lived on Earth are estimated to be

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

. Estimates on the number of Earth's current

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. According to another study, the number of described species has been estimated at 1,899,587. 2000–2009 saw approximately 17,000 species described per year. The total number of undescribed organisms is unknown, but marine microbial species alone could number 20,000,000. For this reason, the number of quantified species will always lag behind the number of described species, and species contained in these lists tend to be on the K side of the r/K selection continuum. More recently, in May 2016, scientists reported that 1

trillion ''Trillion'' is a number with two distinct definitions: * 1,000,000,000,000, i.e. one million million, or (ten to the twelfth power), as defined on the short scale. This is now the meaning in both American and British English. * 1,000,000,000,0 ...

species are estimated to be on Earth currently with only one-thousandth of one percent described. The total number of related DNA

base pair A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...

s on Earth is estimated at 5.0 x 10³⁷ and weighs 50 billion

tonne The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...

s. In comparison, the total

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...

of the

biosphere The biosphere (from Greek βίος ''bíos'' "life" and σφαῖρα ''sphaira'' "sphere"), also known as the ecosphere (from Greek οἶκος ''oîkos'' "environment" and σφαῖρα), is the worldwide sum of all ecosystems. It can also be ...

has been estimated to be as much as 4 TtC (trillion

illion million , is a Japanese singer, songwriter, musician, record producer and actor. Noda is the lead vocalist, songwriter and guitarist of the Japanese rock band Radwimps and also began a solo project, Illion, in 2012. Life and career Early life, Radwi ...

tonnes of

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

). In July 2016, scientists reported identifying a set of 355

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

s from the

Last universal common ancestor The last universal common ancestor (LUCA) is the most recent population from which all organisms now living on Earth share common descent—the most recent common ancestor of all current life on Earth. This includes all cellular organisms; t ...

(LUCA) of all

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...

s living on Earth.

By domain

The

domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a partial function **Domain of holomorphy of a function * Do ...

eukaryotes Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

represent a small minority of the number of organisms; however, due to their generally much larger size, their collective global

biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...

is estimated to be about equal to that of

prokaryotes A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...

. Prokaryotes number about 4–6 × 10³⁰ cells and 350–550 Pg of C.

Microbes

It is estimated that the most numerous bacteria are of a species of the

Pelagibacterales The Pelagibacterales are an order in the Alphaproteobacteria composed of free-living marine bacteria that make up roughly one in three cells at the ocean's surface. Overall, members of the ''Pelagibacterales'' are estimated to make up between a q ...

(or SAR11) clade, perhaps ''

Pelagibacter ubique "''Candidatus'' Pelagibacter", with the single species "''Ca.'' P. communis", was isolated in 2002 and given a specific name, although it has not yet been described as required by the bacteriological code. It is an abundant member of the SAR11 c ...

'', and the most numerous viruses are

bacteriophage A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bacteri ...

s infecting these species. It is estimated that the oceans contain about 2.4 × 10²⁸ (24 octillion) SAR11 cells. The

Deep Carbon Observatory The Deep Carbon Observatory (DCO) is a global research program designed to transform understanding of carbon's role in Earth. DCO is a community of scientists, including biologists, physicists, geoscientists and chemists, whose work crosses sever ...

has been exploring living forms in the interior of the Earth. "Life in deep Earth totals 15 to 23 billion tons of carbon".

Animalia

Vertebrates

Mammals (Mammalia)

* Mammals by population ** Artiodactyla ** Carnivora ** Cetacea ** Chiroptera ** Perissodactyla ** Great apes ** Elephants ** Marsupials

Birds (Aves)

* Birds by population ** Anseriformes ** Apodiformes ** Caprimulgiformes ** Charadriiformes ** Ciconiiformes ** Columbiformes ** Coraciiformes ** Cuculiformes ** Falconiformes ** Galliformes *** The domesticated chicken (Gallus gallus domesticus), a Galliform, has an estimated population of 23.7 billion, which is higher than any other bird. ** Gaviiformes ** Gruiformes ** Passeriformes ** Pelecaniformes ** Phoenicopteriformes ** Piciformes ** Podicipediformes ** Procellariiformes ** Psittaciformes ** Sphenisciformes ** Strigiformes ** Struthioniformes ** Tinamiformes ** Trogoniformes

Reptiles (Reptilia)

Fish (Osteichthyes, Chondrichthyes, and Agnatha)

There are an estimated 3.5 trillion

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

in the ocean.

Hexapoda

Insects (Insecta)

Recent figures indicate that there are more than 1.4 billion insects for each human on the planet, or roughly 10¹⁹ (10 quintillion) individual living insects on the earth at any given time. An article in ''

The New York Times ''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid ...

'' claimed that the world holds 300 pounds of insects for every pound of humans. Ants have colonised almost every landmass on Earth. Their population is estimated as between 10¹⁶–10¹⁷ (10-100 quadrillion). With an estimated 20 quadrillion ants their biomass comes to 12 megatons of dry carbon, which is more than all wild birds and mammals combined.

Plantae

Trees

According to

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

in 2005, there were over 400 billion trees on our globe. However, more recently, in 2015, using better methods, the global tree count has been estimated at 3 trillion. Other studies show that the Amazonian forest alone yields approximately 430 billion trees. Extrapolations from data compiled over a period of 10 years suggest that greater Amazonia, which includes the Amazon Basin and the Guiana Shield, harbors around 390 billion individual trees.

References

{{DEFAULTSORT:Organisms by population Biology-related lists Lists of biota