Global biodiversity is the measure of biodiversity on planet Earth and is defined as the total variability of life forms. More than 99 percent of all species, that ever lived on Earth are estimated to be extinct. Estimates on the number of Earth's current species range from 2 million to 1012, of which about 1.6 million have been databased thus far and over 80 percent have not yet been described. 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 DNA base pairs on Earth, as a possible approximation of global biodiversity, 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 other related studies, around 1.9 million extant species are believed to have been described currently, but some scientists believe 20% are synonyms, reducing the total valid described species to 1.5 million. In 2013, a study published in Science estimated there to be 5 ± 3 million extant species on Earth. Another study, published in 2011 by PLoS Biology, estimated there to be 8.7 million ± 1.3 million eukaryotic species on Earth. Some 250,000 valid fossil species have been described, but this is believed to be a small proportion of all species that have ever lived.
Global biodiversity is affected by extinction and speciation. The background extinction rate varies among taxa but it is estimated that there is approximately one extinction per million species years. Mammal species, for example, typically persist for 1 million years. Biodiversity has grown and shrunk in earth's past due to (presumably) abiotic factors such as extinction events caused by geologically rapid changes in climate. Climate change 299 million years ago was one such event. A cooling and drying resulted in catastrophic rainforest collapse and subsequently a great loss of diversity, especially of amphibians. However, the current rate and magnitude of extinctions are much higher than background estimates. This, considered by some to be leading to the sixth mass extinction, is a result of human impacts on the environment.
Drivers that affect biodiversity
Habitat change (see: habitat fragmentation or habitat destruction) is the most important driver currently affecting biodiversity, as some 40% of forests and ice-free habitats have been converted to cropland or pasture. Other drivers are: overexploitation, pollution, invasive species, and climate change.
Biodiversity is usually plotted as the richness of a geographic area, with some reference to a temporal scale. Types of biodiversity include taxonomic or species, ecological, morphological, and genetic diversity. Taxonomic diversity, that is the number of species, genera, family is the most commonly assessed type. A few studies have attempted to quantitatively clarify the relationship between different types of diversity. For example, the biologist Sarda Sahney has found a close link between vertebrate taxonomic and ecological diversity.
Chapman, 2005 and 2009 has attempted to compile perhaps the most comprehensive recent statistics on numbers of extant species, drawing on a range of published and unpublished sources, and has come up with a figure of approximately 1.9 million estimated described taxa, as against possibly a total of between 11 and 12 million anticipated species overall (described plus undescribed), though other reported values for the latter vary widely. It is important to note that in many cases, the values given for "Described" species are an estimate only (sometimes a mean of reported figures in the literature) since for many of the larger groups in particular, comprehensive lists of valid species names do not currently exist. For fossil species, exact or even approximate numbers are harder to find; Raup, 1986  includes data based on a compilation of 250,000 fossil species so the true number is undoubtedly somewhat higher than this. It should also be noted that the number of described species is increasing by around 18,000-19,000 extant, and approaching 2,000 fossil species each year at the present time, The number of published species names is higher than the number of described species, sometimes considerably so, on account of the publication, through time, of multiple names (synonyms) for the same accepted taxon in many cases.
Based on Chapman's (2009) report, the estimated numbers of described extant species as of 2009 can be broken down as follows:
|Major group||Described||Global estimate (described + undescribed)||Component group||Described||Global estimate||Component group (2)||Described||Global estimate|
|Mesozoa (Rhombozoa, Orthonectida)||106||-|
|Plants sens. lat.||~310,129||~390,800|
|Ferns and allies||~12,000||~15,000|
|Fungi||98,998 (incl. Lichens 17,000)||1,500,000 (incl. Lichens ~25,000)|
|Chromista [incl. brown algae, diatoms and other groups]||25,044||~200,500|
|Protoctista [i.e. residual protist groups]||~28,871||>1,000,000|
|Prokaryota [ Bacteria and Archaea, excl. Cyanophyta]||7,643||~1,000,000|
|Total (2009 data)||1,899,587||~11,327,630|
Estimates of total number of species
However the total number of species for some taxa may be much higher.
- 10-30 million insects;
- 5-10 million bacteria;
- 1.5 million fungi;
- ~1 million mites
- ~1 million protists
In 1982, Terry Erwin published an estimate of global species richness of 30 million, by extrapolating from the numbers of beetles found in a species of tropical tree. In one species of tree, Erwin identified 1200 beetle species, of which he estimated 163 were found only in that type of tree. Given the 50,000 described tropical tree species, Erwin suggested that there are almost 10 million beetle species in the tropics. In 2011 a study published in PLoS Biology estimated there to be 8.7 million ± 1.3 million eukaryotic species on Earth. A 2016 study concludes that Earth is home to 1 trillion species.
Global biodiversity indices
After the Convention on Biological Diversity was signed in 1992, biological conservation became a priority for the international community. There are several indicators used that describe trends in global biodiversity. However, there is no single indicator for all extant species as not all have been described and measured over time. There are different ways to measure changes in biodiversity. The Living Planet Index (LPI) is a population-based indicator that combines data from individual populations of many vertebrate species to create a single index. The Global LPI for 2012 decreased by 28%. There are also indices that separate temperate and tropical species for marine and terrestrial species. The Red List Index is based on the IUCN Red List of Threatened Species and measures changes in conservation status over time and currently includes taxa that have been completely categorized: mammals, birds, amphibians and corals. The Global Wild Bird Index is another indicator that shows trends in population of wild bird groups on a regional scale from data collected in formal surveys. Challenges to these indices due to data availability are taxonomic gaps and the length of time of each index. The Biodiversity Indicators Partnership was established in 2006 to assist biodiversity indicator development, advancement and to increase the availability of indicators.
Importance of biodiversity
Biodiversity is important for humans through ecosystem services and goods. Ecosystem services are broken down into: regulating services such as air and water purification, provisioning services (goods), such as fuel and food, cultural services and supporting services such as pollination and nutrient cycling.
- McKinney 1997, p. 110
- Stearns & Stearns 1999, p. x
- Novacek, Michael J. (8 November 2014). "Prehistory's Brilliant Future". The New York Times. New York: The New York Times Company. ISSN 0362-4331. Retrieved 2014-12-25.
- "Catalogue of Life: 2016 Annual Checklist". 2016. Retrieved 2016-11-06.
- Mora, Camilo; Tittensor, Derek P.; Adl, Sina; et al. (23 August 2011). "How Many Species Are There on Earth and in the Ocean?". PLOS Biology. San Francisco, CA: PLOS. 9 (8): e1001127. doi:10.1371/journal.pbio.1001127. ISSN 1545-7885. PMC . PMID 21886479.
- Staff (2 May 2016). "Researchers find that Earth may be home to 1 trillion species". National Science Foundation. Retrieved 6 May 2016.
- Nuwer, Rachel (18 July 2015). "Counting All the DNA on Earth". The New York Times. New York: The New York Times Company. ISSN 0362-4331. Retrieved 2015-07-18.
- "The Biosphere: Diversity of Life". Aspen Global Change Institute. Basalt, CO. Retrieved 2015-07-19.
- Chapman, A. D. (2009). Numbers of Living Species in Australia and the World (PDF) (2nd ed.). Canberra: Australian Biological Resources Study. pp. 1–80. ISBN 978 0 642 56861 8.
- Costello, Mark; Robert May; Nigel Stork (25 January 2013). "Can we name Earth's species before they go extinct?". Science. 339 (6118): 413–416. doi:10.1126/science.1230318. PMID 23349283.
- Sweetlove, Lee. "Number of species on Earth tagged at 8.7 million". Nature. Macmillan Publishers Limited. Retrieved 18 July 2014.
- Donald R. Prothero (2013), Bringing Fossils to Life: An Introduction to Paleobiology (3rd ed.), Columbia University Press, p. 21
- Sahney, S., Benton, M.J. & Falcon-Lang, H.J. (2010). "Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica" (PDF). Geology. 38 (12): 1079–1082. doi:10.1130/G31182.1.
- Barnosky, A. D.; et al. (2011). "Has the Earth's sixth mass extinction already arrived?". Nature. 471 (7336): 51–57. doi:10.1038/nature09678. PMID 21368823.
- Pereira, HM. "Global Biodiversity Change: The Bad, the Good, and the Unknown". Annual Review of Environment and Resources.
- Sahney, S.; Benton, M.J. (2008). "Recovery from the most profound mass extinction of all time" (PDF). Proceedings of the Royal Society: Biological. 275 (1636): 759–65. doi:10.1098/rspb.2007.1370. PMC . PMID 18198148.[permanent dead link]
- Sahney, S., Benton, M.J. and Ferry, P.A. (2010). "Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land" (PDF). Biology Letters. 6 (4): 544–547. doi:10.1098/rsbl.2009.1024. PMC . PMID 20106856.
- Raup. D.M. (1986). "Biological extinction in earth history". Science. 231 (4745): 1528–1533. doi:10.1126/science.11542058. PMID 11542058.
- IISE (2010). SOS 2009: State of Observed Species (PDF). Arizona State University: International Institute for Species Exploration. pp. 1–8.
- IISE (2011). SOS 2010: State of Observed Species (PDF). Arizona State University: International Institute for Species Exploration. pp. 1–10.
- IISE (2012). SOS 2011: State of Observed Species (PDF). Arizona State University: International Institute for Species Exploration. pp. 1–14.
- Encyclopedia Smithsonian: Numbers of Insects
- Proceedings of the National Academy of Sciences, Census of Marine Life (CoML) BBC News
- David L. Hawksworth, "The magnitude of fungal diversity: the 1•5 million species estimate revisited" Mycological Research (2001), 105: 1422-1432 Cambridge University Press Abstract
- Acari at University of Michigan Museum of Zoology Web Page
- Pawlowski, J. et al. (2012). CBOL Protist Working Group: Barcoding Eukaryotic Richness beyond the Animal, Plant, and Fungal Kingdoms. PLoS Biol 10(11): e1001419. doi:10.1371/journal.pbio.1001419, .
- Adl, S. M. et al. (2007). Diversity, nomenclature, and taxonomy of protists. Systematic Biology 56(4), 684-689, .
- Erwin, Terry L. (March 1982). The Coleopterists Society, ed. "Tropical Forests: Their Richness in Coleoptera and Other Arthropod Species". The Coleopterists Bulletin. 36 (1): 74–75. ISSN 0010-065X. JSTOR 4007977.
- Pullin, Andrew (2002). Conservation Biology. Cambridge: Cambridge University Press. ISBN 9780521644822. Retrieved December 24, 2013.
- "Researchers find that Earth may be home to 1 trillion species". NSF. 2 May 2016. Retrieved 6 May 2016.
- . Zoological Society of London http://www.zsl.org/science/research-projects/indicators-assessments/index,134,ZI.html. Missing or empty
- "Trends in the status of biodiversity". IUCN. Retrieved 25 November 2013.
- "Global Wild Bird Index". Biodiversity Indicators Partnership.
- De Groot, R.S.; et al. (2002). "A typology for the classification, and description and valuation of ecosystem functions, goods and services". Ecological Economics. 41 (3): 393–408. doi:10.1016/s0921-8009(02)00089-7.