Global biodiversity

Known species

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perhaps the most comprehensive recent statistics on numbers of extant species, drawing on a range of published and unpublished sources, and has come up with a figure of approximately 1.9 million estimated described taxa, as against possibly a total of between 11 and 12 million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. 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. The number of described species is increasing by around 18,000–19,000 extant, and approaching 2,000 fossil species each year, as of 2012. 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:

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.

By 2017, most estimates projected there to be around 11 million species or fewer on Earth. A May 2016 study based on scaling laws estimated that 1 trillion species (overwhelmingly microbes) are on Earth currently with only one-thousandth of one percent described, though this has been controversial and a 2019 study of varied environmental samples of 16S ribosomal RNA estimated that there exist 0.8-1.6 million species of prokaryotes.

Indices to describe trends

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.

Biodiversity loss

References

References

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