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A Cumulative Species Description Curve For Large Open Water Marine Animals
Abstract
A cumulative species description curve (from 1830 to 1995) is given for open water marine fauna in excess of 2 m long in the major axis of the body. This curve has not yet closely approached its asymptote. Estimation by maximum likelihood fit of a hyperbola suggests a maximum of some 47 species awaiting formal scientific description and an approximate current rate of description of one new species every 5·3 years. Consideration of the most recently described species and recent observations by field workers suggests that any imminent species descriptions are most likely to be cetaceans.
... In view of the data on recent, continuing discoveries of large marine animals, several workers have examined the discovery and description rates of such animals across time with the aim of determining the number of species that might still await description. By plotting species description rates over time to generate an asymptotic curve, Paxton (1998) found that as many as 47 large openwater marine animals still await description, with an average interval between descriptions of approximately 5.3 years. New data later caused him to raise this figure to 51 (Paxton 2001), but more recent study predicts a lower number (Paxton personal communication 2006). ...
... Description has been largely used in preference to discovery as, even though many years can elapse between the two, description marks the point at which a new species is officially recognised by zoology. This greatly reduces the ambiguity associated with its zoological standing (Paxton 1998). ...
... As was mentioned previously, Paxton (1998) and Raynal (2001) fitted the particular species description records that they studied using non-linear regression. This was achieved using the Michaelis -Menten function, which is most famous for its application in the modelling of enzyme kinetics (Michaelis and Menten 1913). ...
Large extant marine vertebrates continue to be discovered and described: during the late twentieth and early twenty-first century, several cetaceans and chondrichthyans exceeding three metres in total length have been described, including the megamouth shark, Omura's whale, Bandolero (or Peruvian or Lesser) beaked whale, and Perrin's beaked whale. Statistical methods have been employed by several workers in an effort to estimate the number of such species that remain to be described, and results indicate that between 10 and c. 50 such species remain. Here, we examine the description record of the pinnipeds using non-linear and logistic regression models in an effort to determine how many members of this group might remain undescribed. Regression based on a Michaelis–Menten function suggests that as many as 15 such species remain, whilst logistic regression suggests a far lower number (closer to 0). We combine these approaches with an evaluation of cryptozoological data, as ethnozoological evidence suggests the existence of several large-bodied marine vertebrates that have been interpreted by some authors as unusual pinnipeds. These include the so called ‘long-necked sea-serpent’, ‘merhorse’ and ‘tizhurek’. Because cryptozoological data are mostly discussed in the ‘grey literature’, appraisals of these cryptids have never appeared in the mainstream literature, perpetuating a cycle whereby these putative animals remain unevaluated.
... My rational for the small and large size categories is based on the consensus that miniature and small fishes are ≤ 1 cm and < 10 cm, respectively (Moyle and Cech 2004;Helfman et al. 2009), and that there are only 52 species of actinopterygians considered large at > 200 cm (Paxton 1998). The medium and medium-large categories are based on the histogram of the notothenioid length data (Fig. 2) and are judgment calls on my part. ...
... There are only 52 species of large ( > 2 m) actinopterygians (Paxton 1998). With this as the standard for the large category, the two species of Dissostichus are included in a limited group of only about 0.2% (52/30,500) of actinopterygian species, but they are near the lower end of what is considered large given that swordfishes (Xiphiidae) reach 4.5 m (Collette 2002) and oarfishes (Regalecidae) are 8 m long (Roberts 2012;McClain et al. 2015). ...
There has been no comprehensive study of body size in notothenioid fishes. Therefore I evaluated maximum total length (TL) as an axis of the evolutionary radiation. Lengths are provided for 141 species that collectively range in maximum adult size from 5.7 cm (Harpagifer nybelini) to 225 cm (Dissostichus eleginoides), a 39-fold difference. For the 138 species analyzed, the mean length is 33.5 cm and the median is 26.6 cm. Based on 10 cm-bins, notothenioids are apportioned into small (< 10 cm), medium (10–39 cm), medium-large (40–91 cm), and large (> 200 cm) size categories. The 20–29 cm bin contains the most species (32%). Most species (71%) are of medium size, 21% of species are medium-large, and 7% and ≈ 1% are small and large, respectively. The median lengths vary among the five cryonotothenioid families as well as among eight clades (genera and families). Among families, median and mean lengths are smallest in the Harpagiferidae and largest in Channichthyidae. Among clades, Harpagifer has the smallest median length (8.3 cm) followed by Artedidraco (12.5 cm). Several middle-sized clades do not differ in median size: Patagonotothen, Trematomus, Pogonophryne, and Bathydraconidae. Two clades of medium-large size species, Notothenia and Channichthyidae, are of similar size. A significant but weak positive relationship exists between maximum length and maximum depth. With the exception of miniature species ( ≤ 1 cm), the 126 species of cryonotothenioids (the Antarctic clade) encompass the range in size categories in actinopterygians in general, and the disparity in maximum lengths among individual species indicates that body size is an axis of the radiation. I discuss the size of notothenioids relative to other teleosts, the ecological implications of large species in the food web, and the similarity of the cryonotothenioid axes of diversification to those of Lake Baikal sculpins.
... Briefly, in applying this approach, the standard practice is to fit a parametric model with an asymptote to the cumulative discovery record and to estimate the total number of species from the asymptote of the fitted model. For example, in estimating the number of large (i.e. in excess of 2 m in length) marine animals, Paxton (1998) fitted a rectangular hyperbola to the cumulative record of descriptions. The form of this model was chosen for convenience. ...
... The basic model of the discovery record is outlined in x 2. Estimation under this model is covered in x 3. In x 4, the method is applied to the description record of large marine animals compiled by Paxton (1998), and x 5 contains some concluding remarks. ...
A common approach to estimating the number of species in a taxonomic or other group is to extrapolate the temporal pattern of historical species discoveries or descriptions. A formal statistical approach to this problem is described. This approach involves fitting an explicit model of the discovery record by maximum likelihood and using the fitted model to estimate the number of undiscovered species. The approach is applied to a description record of large marine animals covering the period 1828-1996. The estimated number of undiscovered species in this group is around 10 with an upper 0.95 confidence bound of around 16.
... Early species discoveries are often biased toward large-sized, charismatic species with widespread geographic distributions (Essl et al., 2013;Ferretti et al., 2008;Gibbons et al., 2005;Randhawa et al., 2015;Stork et al., 2008Stork et al., , 2015. For instance, positive correlations between species discovery probability and body size have been found in a variety of taxa including insects (Gaston & Hudson, 1994), birds (Blackburn & Gaston, 1995), mammals (Collen et al., 2004;Medellín & Soberón, 1999;Paxton, 1998), fishes (Zapata & Robertson, 2007), reptiles, amphibians (Moura & Jetz, 2021;Reed & Roback, 2002), and marine holozooplanktons (Gibbons et al., 2005). ...
Aim
(1) To understand geographic patterns of species discovery by examining the effect of growth form, range size, and geographic distribution on discovery probability of vascular plant species in China; (2) to find out which taxa harbor the largest number of undiscovered species and where those species locate; and (3) to find out the determinants of province-level mean discovery time and inventory completeness.
Location
China.
Methods
We compiled the discovery time and province-level geographic distributions of ~31,000 vascular plant species described between 1753 and 2013 from Flora of China. We used a Cox proportional hazard model to determine the biological and geographic correlates of discovery probability. Accumulation curves of species discoveries were fitted by a logistic discovery model to estimate inventory completeness of different growth forms and of different provinces. We then used linear regression to identify the determinants of mean discovery time and beta regression to identify the determinants of inventory completeness.
Results
We found that species with larger range size and distributed in northeastern part of China have a higher discovery probability. Coastal species were discovered earlier than inland species. Trees and shrubs of seed plants have the highest discovery probability while ferns have the lowest discovery probability. Herbs have the largest number of undiscovered species in China. Most undiscovered species will be found in southwest China, where three global biodiversity hot spots locate. Spatial patterns of mean discovery time and inventory completeness are mainly driven by the total number of species, human population density in an area, and latitude and longitude of a province.
Main Conclusions
Socioeconomic factors primarily determine the discovery patterns of vascular plants in China. Undiscovered species are most likely to be narrow-ranged, inconspicuous endemic species such as herbs and ferns, which are prone to extinctions and locate in biodiversity hot spots in southwestern China.
... There are additional perspectives on the small number of pelagic cryonotothenioids. Large (> 2 m) pelagic actinopterygians, such as the two species of Dissostichus, are rare in general (Paxton 1998), and divergence into the pelagic and semipelagic biotopes in fishes without a swim bladder requires, as previously noted, substantial morphological alteration. The physical properties of cold seawater may also limit divergence into water column habitats. ...
In the absence of any prior comprehensive analysis, I evaluate divergence along the biotope axis in the habitat stage of the evolutionary radiation of Antarctic cryonotothenioids. I utilize the available percentage buoyancy (%B) measurements as habitat proxies for recognition of the pelagic, semipelagic, demersal, and benthic biotopes that include, respectively, 5%, 10%, 73%, and 12% of the 59 species and 1749 specimens in the study. The majority of species retain the ancestral demersal biotope of Eleginops maclovinus, and this probably enhances ecological plasticity. Divergence into the pelagic biotope is the most distinctive organismal feature of the radiation and, although only 5% of species are pelagic, this biotope is not depauperate in global comparisons. Pelagic or potentially pelagic species are Dissostichus mawsoni, D. eleginoides, Pleuragramma antarctica, Aethotaxis mitopteryx, and Gvozdarus svetovidovi. Small ontogenetic changes in %B with growth are typical; however, this is extensive in D. mawsoni, a species with the potential to transition through benthic to pelagic biotopes over ontogeny. Occupation of the pelagic biotope by large D. mawsoni may be impermanent as it is lipid-dependent, a contingency reliant on the availability of P. antarctica as prey. In unusual conditions, the specialized sacs of P. antarctica can also yield their lipid for metabolism with possible loss of buoyancy. Pelagic species are inordinately important in the food web. In the southwestern Ross Sea a guild of large mammalian and avian predators, which includes D. mawsoni, is reliant on lipid-rich, energy-dense cryonotothenioid prey. This includes asymmetrical intraguild predation on D. mawsoni, with P. antarctica as a basal resource for the guild.
... Early species discoveries are often biased toward large-sized, charismatic species with widespread geographic distributions (Essl et al., 2013;Ferretti et al., 2008;Gibbons et al., 2005;Randhawa et al., 2015;Stork et al., 2008Stork et al., , 2015. For instance, positive correlations between species discovery probability and body size have been found in a variety of taxa including insects (Gaston & Hudson, 1994), birds (Blackburn & Gaston, 1995), mammals (Collen et al., 2004;Medellín & Soberón, 1999;Paxton, 1998), fishes (Zapata & Robertson, 2007), reptiles, amphibians (Moura & Jetz, 2021;Reed & Roback, 2002), and marine holozooplanktons (Gibbons et al., 2005). ...
In order to understand the patterns of plant discoveries in China and find out which taxa and which areas harbor most numbers of undiscovered species, we analyzed the discovery times of 25268 vascular plant species described between 1753 and 2000 from Flora Reipublicae Popularis Sinicae. We found that species with larger range size and distributed in northeastern part of China have a higher discovery probability. Species distributed on the coast were discovered earlier than inland species. Herbs have the highest discovery probability and ferns have the lowest discovery probability. Ferns and herbs have the largest number of undiscovered species in China. Most undiscovered species are found in southwestern part of China, one of the biodiversity hotspots in the world. Spatial patterns of mean discovery time and inventory completeness are mainly driven by the total number of species and human population density in an area and whether the area is coastal or not. We demonstrated that socio-economic factors shape the discovery patterns of vascular plants in China. Undiscovered species are mostly narrow-ranged, inconspicuous endemic species such as herbs and ferns, which are prone to extinctions and locate in biodiversity hotspots in southwestern China.
... It is possible to estimate total species richness using extrapolation based on species accumulation curves (Colwell & Coddington, 1994). For instance, Paxton (1998) estimated the total number of large marine animals using this approach. The major difficulty with this method is to assemble adequate datasets. ...
Cumulative species description curves since 1758 are given for all termites of the world and for each biogeographical region (Australian, Ethiopian, Nearctic, Neotropical, Oriental, Palearctic, and Papuan). A cumulative description curve is also given for world genera. Estimation by maximum likelihood using the Michaelis-Menten model suggests a maximum of 5366 ± 175 species (p < 2.2E-16) and 704 ± 77 genera (p < 4.387E-13). Model fitting was poor for most individual biogeographical regions, with the exception of the Ethiopian region (estimate = 1295 ± 57 species, p < 2.2E-16). World War I and World War II had marked negative impacts on termite description rates. Data from China was treated separately due to the atypical rate of description of new termites in that country during the last two decades of the 20th century.
... A useful approach to predicting the development of specific inventories is the analysis of the temporal trends in species descriptions, whereby rapidly climbing curves could indicate an incompletely documented fauna, whereas flat curves may suggest that the proportion of undescribed species is low (Costello et al., 1996;Paxton, 1998;Clarke and Johnston, 2003). We compared such curves for two conspicuous and very well-researched groups of vertebrates (Primates and Reptilia), 1599 zooplanktonic species (several groups) recorded in the South Atlantic, and three groups of Antarctic benthic invertebrates (Fig. 3). ...
In total, ca. 7000 zooplanktonic species have been described for the World Ocean. This figure represents less than 4% of the total number of known marine organisms. Of the 7000 zooplanktonic species world-wide, some 60% are present in the South Atlantic; about one third of the latter have been recorded in its Subantarctic waters, and ca. 20% south of the Polar Front. When compared with those of benthic animals, these figures indicate that proportions of the overall inventories that are present in the cold waters are almost two times higher among the zooplankton. In agreement with this pattern, the proportions of Antarctic endemics in the benthos are very significantly higher than those in the plankton. For the water-column dwelling animals, the Polar Front boundary is more important than the Tropical-Subtropical limit, but almost equivalent to the Subtropical-Transitional limit, and weaker in biogeographic terms than the Transitional-Subantarctic boundary. Some of the implications of these dissimilarities, both for ecological theory and for resource allocation strategies, are discussed.
... Several workers have assessed such data and reported their fi ndings in the peer-reviewed technical literature (e.g., Scott and Rines, 1975, Raynal & Sylvestre, 1991, Paxton & Holland, 2005, Paxton, 2009. Critical discussions of large undescribed species are not necessarily outlandish, as numerous marine vertebrate megafaunal species (>45 kg) have been discovered and described in recent years (e.g., Megamouth shark Megachasma pelagios Taylor et al., 1983, Bandolero beaked whale Mesoplodon peruvianus Reyes et al., 1991, West African skate Bathyraja hesperafricana Stehmann, 1995, Indonesian coelacanth Latimeria menadoensis Pouyaud et al., 1999, and statistical work suggests that several such species remain to be documented (Paxton, 1998, Raynal, 2001, Solow & Smith, 2005. Large marine vertebrates can be surprisingly cryptic due to rarity, habitat, and/or avoidance of vessels (Heyning, 1989); Megachasma pelagios was not recorded from the Atlantic until 1995 (Amorim et al., 2000); the family Ziphiidae ("beaked whales") includes numerous poorly known species, including Mesoplodon traversii, which is known from three partial skulls and has no live records (van Helden et al., 2002). ...
Eyewitness reports and cultural representations have been interpreted by some researchers to suggest the existence of a large, long-bodied marine vertebrate in the northeast Pacifi c. Dubbed “Caddy” or “Cadborosaurus” (after Cadboro Bay, British Columbia), it was formally named and described as Cadborosaurus willsi by Bousfi eld and LeBlond in 1995. Among the supposedly most informative accounts is the alleged 1968 capture of a juvenile by William Hagelund, detailed in his 1987 book Whalers No More. Reportedly morphologically similar to adult “Cadborosaurs,” the specimen was comparatively tiny, and apparently precocial. Bousfield and LeBlond argue that this strongly supports their contention that “Caddy” is reptilian (juvenile
reptiles are typically precocial, recalling “miniature adults” in both behavior and morphology). Anomalous traits suggest some degree of misrecollection in Hagelund’s account, furthermore a quantitative analysis of the similarity of 14 candidate identities with the specimen indicates that it most strongly resembles the bay pipefi sh (Syngnathus leptorhynchus)—far more so than a cryptid or reptile. While this detracts from the plausibility of the cryptid, the reidentification of this particular specimen does not discount the data as a whole nor does it suggest that all “Caddy” reports are necessarily of known fish. We contend that the “reptilian hypothesis” does, however, need to be seriously re-examined in light of the removal of a strong piece of evidence.
... When describing new species, a genetic description should also be included wherever possible. A recent analysis of discovery trends has suggested that at least 40 species of large marine animals still remain to be described (Paxton 1998). If so, it is likely that several new cetacean species will be among them, including at least one new form of Bryde's whale, Balaenoptera edeni sp. ...
Mesoplodon perrini, a new species of beaked whale is described on the basis of five animals stranded on the coast of California (between 3255N, 11715W and 3637N, 12155W) from May 1975 to September 1997. Four of these animals were initially identified as Hector's beaked whales M. hectori based on cranial morphology (Mead 1981). A fifth specimen was ini- tially identified as a neonate Cuvier's beaked whale Ziphius cavirostris based on external features. These specimens were first recognized as representatives of an undescribed species through phylogenetic analysis of mitochondrial (mt) DNA control region and cytochrome b sequence data. Although similar mor- phologically, the genetic data do not support a close evolutionary relationship between M. perrini and M. hectori. Instead, these data suggest a possible sister-
... In the marine environment, large (42 m) marine animals are still being described (Paxton, 1998 (Dalebout et al.)]; but also clearly morphologically new species [e.g. Bathyraja hesperafricana, a giant benthic ray described in 1995 (Stehmann)]. ...
Analysis of the nearest reported distance in accounts of seemingly unknown, large, marine animals (sea monsters) by boat- or water-based eyewitnesses, revealed that, contrary to expectation, the majority of sightings were at close distance (<200 m). This suggests that misidentification of inanimate objects or known animal species due to great distance was unlikely. Assuming a uniform distribution of objects around the boat, the reported sightings were far closer than expected, implying a bias in the sighting or reporting process. The distribution of reported distances from boat- or water-based eyewitnesses was almost identical to that of shore-based witnesses. Unidentified large marine animals were more likely to be reported to be closer if the report was anonymous or secondhand. The gap of time between recollection/reporting and the actual sighting did not influence reported distance. There was no relation between reported distance and reported length. There was some equivocal evidence that the absence of a stated distance in a report might be an indicator of a hoax.
... see Held, 2005), the unbalance between biodiversity in the plankton and in the benthos will increase several-fold. A useful approach to predicting the development of specific inventories is the analysis of the temporal trends in species descriptions, whereby rapidly climbing curves could indicate an incompletely documented fauna, whereas flat curves may suggest that the proportion of undescribed species is low (Costello et al., 1996; Paxton, 1998; Clarke and Johnston, 2003 ). We compared such curves for two conspicuous and very well-researched groups of vertebrates (Primates and Reptilia), 1599 zooplanktonic species (several groups) recorded in the South Atlantic, and three groups of Antarctic benthic invertebrates (Fig. 3). ...
: In total, ca. 7000 zooplanktonic species have been described for the World Ocean. This figure represents less than 4% of the total number of known marine organisms. Of the 7000 zooplanktonic species world-wide, some 60% are present in the South Atlantic; about one third of the latter have been recorded in its Subantarctic waters, and ca. 20% south of the Polar Front. When compared with those of benthic animals, these figures indicate that proportions of the overall inventories that are present in the cold waters are almost two times higher among the zooplankton. In agreement with this pattern, the proportions of Antarctic endemics in the benthos are very significantly higher than those in the plankton. For the water-column dwelling animals, the Polar Front boundary is more important than the Tropical-Subtropical limit, but almost equivalent to the Subtropical-Transitional limit, and weaker in biogeographic terms than the Transitional-Sub-antarctic boundary. Some of the implications of these dissimilarities, both for ecological theory and for resource allocation strategies, are discussed.
... This may seem surprising, given that expedition accounts of natural historians from the 18th and 19th centuries conjure up images of discovery on a grand scale that seemingly cannot be matched todaylook in the rocks … a new fossil mammal; look in the lake … a new fish genus; look on the dinner plate … a new species of bird. Finding new large vertebrates nowadays is indeed newsworthy, but a new species of large mammal is still discovered roughly every three years 5 and a new large vertebrate from the open ocean every five years 6 . And most organisms are much smaller than these are. ...
The term 'biodiversity' is a simple contraction of 'biological diversity', and at first sight the concept is simple too: biodiversity is the sum total of all biotic variation from the level of genes to ecosystems. The challenge comes in measuring such a broad concept in ways that are useful. We show that, although biodiversity can never be fully captured by a single number, study of particular facets has led to rapid, exciting and sometimes alarming discoveries. Phylogenetic and temporal analyses are shedding light on the ecological and evolutionary processes that have shaped current biodiversity. There is no doubt that humans are now destroying this diversity at an alarming rate. A vital question now being tackled is how badly this loss affects ecosystem functioning. Although current research efforts are impressive, they are tiny in comparison to the amount of unknown diversity and the urgency and importance of the task.
... However, they did not predict how many species remained to be discovered. Paxton (1998) fitted a regression line to the post-1830 part of the discovery rate curve for 217 large (greater than 2 m wide or long) marine animals to predict that 47 more (20%) species awaited description in the world. Wittman (1999) looked at the global diversity of mysid crustaceans and, on the basis of comparisons of discovery rates in different latitudes and regions, predicted it to be four times greater than the number of species described. ...
Predicting future rates of species discovery and the number of species remaining are important in efforts to preserve biodiversity, discussions on the rate of species extinction and comparisons on the state of knowledge of animals and plants of different taxa. Data on discovery dates of species in 32 European marine taxa are analysed by using a class of thinned temporal renewal process models. These models allow for both underdispersion and overdispersion with respect to the non-homogeneous Poisson process. An approach for implementing Bayesian inference for these models is described that uses Markov chain Monte Carlo simulation and that is applicable to other types of thinned process. Predictions are made on the number of species remaining to be discovered in each taxon. Copyright 2005 Royal Statistical Society.
The Indus Script originates from the culture known as the Indus Valley Civilization, which flourished from approximately 2600 to 1900 bc. Several thousand objects bearing these signs have been found over a wide area of Northern India and Pakistan. In 1977, Iravatham Mahadevan published a concordance of all of the scripts that had been discovered so far. Accompanying the concordance are a set of nine tables showing the distribution of individual signs by position, archaeological site, object type, field symbol (accompanying image), and direction of writing. Analysis of the frequencies of the signs found so far using Large Numbers of Rare Events (LNRE) models estimated the total vocabulary of the language, including signs not yet found, to be about 857. All the tables were analysed using Pearson’s residuals, and it was found that the signs were not randomly distributed, but some showed statistically significant associations with position, object, field symbol or direction of writing. A more detailed analysis of the relation between signs and field symbols was made using correspondence analysis, which showed that certain signs were associated with the unicorn symbol, while others were associated with the gharial and dotted circle symbols.
Mesoplodon perrini, a new species of beaked whale is described on the basis of five animals stranded on the coast of California (between 32°55′N, 117°15′W and 36°37′N, 121°55′W) from May 1975 to September 1997. Four of these animals were initially identified as Hector's beaked whales M. hectori based on cranial morphology (Mead 1981). A fifth specimen was initially identified as a neonate Cuvier's beaked whale Ziphius cavirostris based on external features. These specimens were first recognized as representatives of an undescribed species through phylogenetic analysis of mitochondrial (mt) DNA control region and cytochrome b sequence data. Although similar morphologically, the genetic data do not support a close evolutionary relationship between M. perrini and M. hectori. Instead, these data suggest a possible sister-species relationship with the lesser beaked whale M. peruvianus. Sightings of two small beaked whales off California in the 1970s which were tentatively identified as M. hectori are also likely to be M. perrini. We suggest that M. hectori is confined to the Southern Hemisphere, while M. perrini is known to date only from the North Pacific.
Although the number of biodiversity studies is increasing, the total number of species in different taxonomic groups remains uncertain. Estimates of the number of described species of Cyanobacteria range from 2,000 to 8,000. However, no studies have used discovery curves to estimate this number. The aim of this study was to understand the status of cyanobacterial biodiversity on a global scale and to estimate the number of still-unknown species, using a discovery curve. The species and year of descriptions of Cyanobacteria were obtained from the CyanoDB database. The cumulative number of species per year was adjusted using three asymptotic models (Logistic, Gompertz, and Extreme Value). These nonlinear models were compared through the Akaike information criterion. There are currently 2,698 described species of Cyanobacteria, and the best model (Gompertz) estimated that this group must contain 6,280 species. These three models proved to be quite idiosyncratic (Extreme value: 3,166 species and Logistic: 3,769 species), and therefore the choice of model is fundamental in studies using a discovery curve. Many Cyanobacteria species remain to be described, demonstrating the importance of increasing investment in research on the biodiversity of Cyanobacteria, in particular in understudied geographic regions.
Plenty more fish in the sea? But how can one tell? And what strange creatures remain to be discovered? The largest ever survey of marine life has just been concluded. Andrew R. Solow and Derek Tittensor tell us of new species and species that are no more, and wonder if we shall ever see a Caribbean monk seal again.
Aim In this paper, we compare species description rates to predict the numbers of undescribed species. These data are used to discuss the merits of various attempts to estimate species richness in the oceans.
Location European marine areas.
Methods Predictions of how many species may exist on Earth have lacked an inventory of how many have been described, except for a few small taxa. The ocean is a good place to start an inventory because it includes all but one of the phyla and most classes of life on Earth. The European Register of Marine Species (ERMS) was compiled by taxonomic experts, covered all marine taxa, and accounted for synonyms. Reflecting taxonomic history, Europe's species are the best described in the world.
Results ERMS listed 29,713 species of animals, plants and protists, but excluded bacteria and viruses. An estimated 6500 described species were not included. The best prediction of the number of species remaining to be described was 5613. Plots of years when species were first described showed no decrease in the rate of description for any taxa except birds, mammals and krill. If taxonomic effort has increased, whether due to more resources globally or greater efficiencies of productivity, then description rates per unit effort may be declining and the number of undescribed species may be lower than predicted. However, apart from reduced rates of description during the World Wars, there were no changes in description rates that could be easily attributed to such factors.
Conclusions There are about 36,000 species described from European seas, and we predict that 40,000 to 48,000 may exist. This comprises 15% of the estimated 230,000 described marine species. However, this area is well known compared with other seas and the proportion of species yet to be discovered will be higher elsewhere.
Both the magnitude and the urgency of the task of assessing global biodiversity require that we make the most of what we know through the use of estimation and extrapolation. Likewise, future biodiversity inventories need to be designed around the use of effective sampling and estimation procedures, especially for 'hyperdiverse' groups of terrestrial organisms, such as arthropods, nematodes, fungi, and microorganisms. The challenge of estimating patterns of species richness from samples can be separated into (i) the problem of estimating local species richness, and (ii) the problem of estimating the distinctness, or complementarity, of species assemblages. These concepts apply on a wide range of spatial, temporal, and functional scales. Local richness can be estimated by extrapolating species accumulation curves, fitting parametric distributions of relative abundance, or using non-parametric techniques based on the distribution of individuals among species or of species among samples. We present several of these methods and examine their effectiveness for an example data set. We present a simple measure of complementarity, with some biogeographic examples, and outline the difficult problem of estimating complementarity from samples. Finally, we discuss the importance of using 'reference' sites (or sub-sites) to assess the true richness and composition of species assemblages, to measure ecologically significant ratios between unrelated taxa, to measure taxon/sub-taxon (hierarchical) ratios, and to 'calibrate' standardized sampling methods. This information can then be applied to the rapid, approximate assessment of species richness and faunal or floral composition at 'comparative' sites.
An application of the method of maximum likelihood (ML) is described for analysing the results of enzyme kinetic experiments in which the Michaelis-Menten equation is obeyed. Accurate approximate solutions to the ML equations for the parameter estimates are presented for the case in which the experimental errors are of constant relative magnitude. Formulae are derived that approximate the standard errors of these estimates. The estimators are shown to be asymptotically unbiased and the standard errors observed in simulated data rapidly approach the theoretical lower bound as the sample size increases. The results of a large-scale Monte Carlo simulation study indicate that for data with a constant coefficient of variation, the present method is superior to other published methods, including the conventional transformations to linearity and the nonparametric technique proposed by Eisenthal and Cornish-Bowden (1974, Biochemical Journal 139, 715-720). Finally, the present results are extended to the analysis of simple receptor binding experiments using the general approach described by Munson and Rodbard (1980, Analytical Biochemistry 107, 220-239).
An account of Cadborosaurus willsi, new genus, new species, a large aquatic reptile from the Pacific coast of North America
- Bousfield