question: How often are new species are being discovered? How are we still constantly discovering new ones?
comment: I answered a question on r/askscience a [few weeks ago]( URL_11 ) that might help you a bit, though the focus was more on the process of how new species are identified than the rate of discovery. I'll copy it here too if it helps: > Going out into the field on big expeditions certainly used to be the main way that new species were identified; Linnaeus famously had a whole group of "[apostles]( URL_1 )" who travelled all over the world describing new species and collecting specimens (several of them [died in the process]( URL_0 )). However, in practice most species that are described in modern times are identified in labs and museums. > > Though this depends a lot on what groups of organisms you're focused on, it's fairly safe to say that, in the case of large terrestrial animals at least, we've discovered a very large percentage of existing biodiversity. However, dividing these organisms up into species is not an exact science, since there are a variety of [different definitions]( URL_2 ) of what a species is that can be used. For example, though the biological species concept (i.e., species are groups of organisms that breed and produce fertile offspring) is perhaps the most common, it is flawed in several ways, not least of which being that it is obviously inapplicable to asexually reproducing organisms. The impracticality of actually carrying out breeding trials also often leads to other methods being used. Phylogenetic approaches to defining species have been fairly common in this century; a recent high-profile example being the splitting of giraffes into four species based on DNA analysis by [Fennessy et al]( URL_4 ). As is almost always the case with charismatic animals though, this study is [not free from criticism]( URL_9 ). And, though this is getting a bit off topic, such distinctions have important real-world consequences, like how we manage conservation of animals which are not endangered when regarded as a single species, but may have critically endangered sub-groups. > > Then, there's also a good number of species being described that have already been collected in the field previously, but never studied. Museums tend to accumulate humongous collections that often include many specimens which never see the light of day after being stored, and going back through these is an easy way for new species to be found. [Here's an article]( URL_8 ) showing a few good examples of this. This kind of discovery is probably especially common for insects (which still make up around [half of new species being described]( URL_6 )), where collections often have specimens numbering in the [tens of millions]( URL_5 ). Anecdotally, I have a friend who is currently working on publishing a new species he described which he found in a "miscellaneous" bin of specimens. > > So in summary, it varies a lot depending on what groups of organisms you're interested in. Some things, like fungi, microbes, [nematodes]( URL_10 ), and other small and infrequently collected groups are [stupendously underrepresented]( URL_3 ) in our current knowledge of global biodiversity, and should continue to be explored by collecting field specimens (many would argue that the numbers in that figure are significant underestimates too). Other groups, like vertebrates as previously mentioned, are already mostly "discovered", but the number of recognized species varies depending on how species are defined and in some cases conservation concerns. In general, we can use [species accumulation curves]( URL_7 ), which compare number of described species over time (adjusted for amount of effort put into looking), to get an idea of how close we are to the asymptotic limit of identifying all species on Earth, but for most groups of life we are still well below this point. The last section of this is probably most relevant for your question; in general, it is true that rates of species discovery for many groups are indeed slowing down (at least when corrected for amount of work put in). However, there are also many groups of organisms that have received very little attention historically, and for which thousands of new species are probably awaiting discovery if anyone bothers to go look for them!
passages: Animal sentinels must have measurable responses to the hazard in question, whether that is due to the animal's death, disappearance, or some other determinable aspect. Many of these species are ideally unendangered and easy to handle. It is important that the species' range overlap with the range being studied. Often the ideal species is determined by the characteristics of the hazard.
   New species are regularly discovered (on average between 5–10,000 new species each year, most of them insects) and many, though discovered, are not yet classified (estimates are that nearly 90% of all arthropods are not yet classified). Most of the terrestrial diversity is found in tropical forests and in general, land has more species than the ocean; some 8.7 million species may exists on Earth, of which some 2.1 million live in the ocean.
  
  Section::::Ecosystem services.
  
  Section::::Ecosystem services.:The balance of evidence.
   The IISE also releases an annual report that inventories the complete list of species cataloged two years prior and discusses the state of new species discovery. The 2011 report, for example, found that 19,232 species were named in 2009, a 5.6% increase over the prior year. The report takes about two years to compile due to the lack of standardized registration for new species, and issue which IISE has campaigned for. It routinely finds that insects make up roughly half of all new species discovered, followed by vascular plants and arachnids.
  
  Section::::External links.
  
  BULLET::::- Homepage
   If species richness of the obtained sample is taken to represent species richness of the underlying habitat or other larger unit, values are only comparable if sampling efforts are standardised in an appropriate way. Resampling methods can be used to bring samples of different sizes to a common footing. Properties of the sample, especially the number of species only represented by one or a few individuals, can be used to help estimating the species richness in the population from which the sample was drawn.
  
  Section::::Trends in species richness.
   The measure of ongoing species loss is made more complex by the fact that most of the Earth's species have not been described or evaluated. Estimates vary greatly on how many species actually exist (estimated range: 3,600,000-111,700,000) to how many have received a species binomial (estimated range: 1.5-8 million). Less than 1% of all species that have been described beyond simply noting its existence. From these figures, the IUCN reports that 23% of vertebrates, 5% of invertebrates and 70% of plants that have been evaluated are designated as endangered or threatened. Better knowledge is being constructed by The Plant List for actual numbers of species.
   Individual countries particularly rich in species newly described during this period are:
  
  BULLET::::- Brazil
  
  BULLET::::- Colombia
  
  BULLET::::- Peru
  
  BULLET::::- Indonesia
  
  BULLET::::- Philippines
  
  A number of individuals have been particularly prolific in describing new species, such as:
  
  BULLET::::- Niels Krabbe
  
  BULLET::::- Paul Coopmans
  
  BULLET::::- Bret Whitney
  
  Section::::Species described that were not valid species.
  
  A number of species described during this period have turned out not to be valid species. There are a number of reasons for this. The following is a list of these species:
   All ATBIs are inherently incomplete since, a) the biota of even well-studied areas includes many undescribed and often difficult-to-study species, and b) new species are regularly established through immigration and introduction.
  
  A study assessed the species richness of megadiverse order of insects as a result of Zurquí All Diptera Biodiversity Inventory project at Costa Rica for one year, identifying more than 40000 flies to 4332 species, including 73 of the world's 160 Diptera families.
  
  Section::::See also.
  
  BULLET::::- Biodiversity
  
  BULLET::::- Measurement of biodiversity
  
  Section::::External links.
   The fossil record concerning insects stretches back for hundreds of millions of years. It suggests there are ongoing background levels of both new species appearing and extinctions. Very occasionally, the record also appears to show mass extinctions of insects. The Permian–Triassic extinction event saw the greatest level of insect extinction, with the Cretaceous–Paleogene being the second highest. Insect diversity has recovered after past mass extinctions, due to periods where new species originate with increased frequency, though the recovery can take millions of years.
  
  Section::::Species diversity.:In the Holocene.
   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.
   On that note, rare today does not mean rare tomorrow. Given the persistence of these taxa under the right conditions they have the potential to dominate, and become the more abundant taxa. The occurrence of such conditions may occur on many temporal scales. It may be possible that some rare taxa dominate only during anomalous years, such as during El Niño. While, a four-year study by Brown et al. in species abundance in a single marine ecosystem found that some taxa were undetectable during some months and accounted for a couple percent of the total abundance other months. Indicating that a change in abundance may occur on a seasonal scale. Recent global climate change may provide some of these rare taxa with the conditions necessary to increase in abundance.
   Several studies seemed to indicate that some insect populations are in decline in the late 20th and early 21st centuries, and has also been popularized as the windshield phenomenon. For many studies, factors such as abundance, biomass, and species richness are often found to be declining for some, but not all locations in many studies; some species are in decline while others are not. Every species is affected in different ways by changes in the environment, and it cannot be inferred that there is a consistent decrease across different insect groups. When conditions change, some species easily adapt to the change while others struggle to survive.
   This article describes bird species discovered since 1900. Before the 20th century, and into its early decades, the pace of discovery (and "discovery") of new species was fast; during this period, with numerous collecting expeditions into species-rich areas not previously visited by western ornithologists, up to several hundred new species per decade were being described. Many of these were of course not new to the local people, but since then, the pace has slowed, and new species are generally only being found in remote areas, or among cryptic or secretive groups of species. Nonetheless, several tens of species were described for the first time even during the 1990s. Considerable time can pass between discovery and publication, for a number of reasons.
   Over nine-tenths of the total biomass on Earth is plant life, on which animal life depends very heavily for its existence. More than 2 million species of plant and animal life have been identified to date, and estimates of the actual number of existing species range from several million to well over 50 million. The number of individual species of life is constantly in some degree of flux, with new species appearing and others ceasing to exist on a continual basis. The total number of species is in rapid decline.
  
  Section::::Life.:Evolution.
   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 1.9 million are estimated to have been named and 1.6 million documented in a central database to date, leaving at least 80 percent not yet described.
   The mechanism by which a key innovation leads to taxonomic diversity is not certain but several hypotheses have been suggested:
  
  Section::::Mechanism.:Increasing individual fitness.
  
  A key innovation may, by increasing the fitness of individuals of the species, result in extinction becoming less likely and allow the taxa to expand and speciate.
   Attempts have been made to identify new locations where the species could occur based on identification of suitable habitats using computational models.
  
  Section::::Species discovery.
   Based on Chapman's (2009) report, the estimated numbers of described extant species as of 2009 can be broken down as follows:
  
  Section::::Estimates of total number of species.
  
  However the "total" number of species for some taxa may be much higher. 
  
  BULLET::::- 10–30 million insects;
  
  BULLET::::- 5–10 million bacteria;
  
  BULLET::::- 1.5 million fungi;
  
  BULLET::::- ~1 million mites
  
  BULLET::::- ~1 million protists
   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. 
   BULLET::::- "Ceratitis capitata" (Mediterranean fruit fly) 
  
  BULLET::::- "Cryptotermes brevis" (West Indian drywood termite)
  
  BULLET::::- "Culex quinquefasciatus" (southern house mosquito) 
  
  BULLET::::- "Frankliniella occidentalis" (western flower thrips) 
  
  BULLET::::- "Hypogeococcus pungens" (cactus mealybug) 
  
  BULLET::::- "Icerya purchasi" (cottony cushion scale)
  
  BULLET::::- "Maconellicoccus hirsutus" (pink hibiscus mealybug) 
  
  BULLET::::- "Papilio demoleus" (common lime butterfly)
  
  BULLET::::- "Paracoccus marginatus" (papaya mealybug)
  
  BULLET::::- "Paratachardina pseudolobata" (lobate lac scale)
  
  BULLET::::- "Pheidole megacephala" (big-headed ant) 
  
  BULLET::::- "Phenacoccus solenopsis" (cotton mealybug) 
  
  BULLET::::- "Phyllocnistis citrella" (citrus leafminer)
  
  BULLET::::- "Sternochetus mangiferae" (mango seed weevil)
  
  BULLET::::- "Tapinoma melanocephalum" (ghost ant)
  
  BULLET::::- "Thrips palmi" (melon thrips)
   Removal of exotic species will allow the species that they have negatively impacted to recover their ecological niches. Exotic species that have become pests can be identified taxonomically (e.g., with Digital Automated Identification SYstem (DAISY), using the barcode of life). Removal is practical only given large groups of individuals due to the economic cost.
  
  As sustainable populations of the remaining native species in an area become assured, "missing" species that are candidates for reintroduction can be identified using databases such as the "Encyclopedia of Life" and the Global Biodiversity Information Facility.
   Searches for "Naultinus" are often inconclusive because the animals simply avoid detection. Improved detection methods would allow scientists to monitor populations much more accurately and a number of different studies in recent years have been doing research into this area – some key ideas are a new type of cover mounted on trees for animals to hide in, pheremone lures and even terriers trained to pick up on the scent of native geckos. "Naultinus" have been reintroduced to some predator free areas and are present at other locations where their habitat is protected and where pest control is being carried out but because "Naultinus" have a very slow breeding rate, recovery of populations is inevitably a relatively slow and gradual process.
   These developments could not have come at a better time. As the taxonomic community already knows, the world is running out of specialists who can identify the very biodiversity whose preservation has become a global concern. In commenting on this problem in palaeontology as long ago as 1993, Roger Kaesler recognized:
   Analysis of DNA sequences is becoming increasingly standard for species recognition and may in many cases be the only useful method. Different methods are used to analyse such genetic data, for example molecular phylogenetics or DNA barcoding. Such methods have greatly contributed to the discovery of cryptic species, including such emblematic species as the fly agaric or the African elephants.
  
  Section::::Evolution and ecology.
  
  Section::::Evolution and ecology.:Speciation process.
   Depending on the purposes of quantifying species richness, the individuals can be selected in different ways. They can be, for example, trees found in an inventory plot, birds observed from a monitoring point, or beetles collected in a pitfall trap. Once the set of individuals has been defined, its species richness can be exactly quantified, provided the species-level taxonomy of the organisms of interest is well enough known. Applying different species delimitations will lead to different species richness values for the same set of individuals. 
   Once a niche is left vacant, other organisms can fill that position. For example, the niche that was left vacant by the extinction of the tarpan has been filled by other animals (in particular a small horse breed, the konik). Also, when plants and animals are introduced into a new environment, they have the potential to occupy or invade the niche or niches of native organisms, often outcompeting the indigenous species. Introduction of non-indigenous species to non-native habitats by humans often results in biological pollution by the exotic or invasive species.
  