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This is a collection of lists of organisms by their population. While most 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 and biogeography. Individuals are counted by census, as carried out for the piping plover; using the transect method, as done for the mountain plover; and beginning in 2012 by satellite, with the emperor penguin being the first subject counted in this manner.
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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. Estimates on the number of Earth's current species 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. The number of quantified species will ipso facto 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 species are estimated to be on Earth currently with only one-thousandth of one percent described. The total amount of related DNA base pairs on Earth is estimated at 5.0 x 1037 and weighs 50 billion tonnes. In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC (trillion tons of carbon). In July 2016, scientists reported identifying a set of 355 genes from the Last Universal Common Ancestor (LUCA) of all organisms living on Earth.
Microbes
It is estimated that the most numerous bacteria are of a species of the Pelagibacterales (or SAR11) clade, perhaps Pelagibacter ubique, and the most numerous viruses are bacteriophages infecting these species. It is estimated that the oceans contain about 2.4 × 1028 (24 billion billion billion) SAR11 cells.
Mammals (Mammalia)
Birds (Aves)
Fish (Osteichthyes+Chondrichthyes+Agnatha)
There are an estimated 3,500,000,000,000 (3.5 trillion) fish in the ocean. In the last 100 years, the number of small fish – such as pilchards, herrings, anchovies, sprats and sardines – has more than doubled. It is caused by a major decline in big ‘predator fish’ such as sharks, tuna and cod due to over-fishing.
Insects (Insecta)
Recent figures indicate that there are more than 200 million insects for each human on the planet. An article in The New York Times 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 107–108 billion.
Plantae
According to NASA 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 about 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.