Sunday, May 26, 2013

How many species of snakes and other squamates are there? Part 2. And, the bigger problem.

The on-line Reptile Database lists 8,734 species of reptiles (squamates, chelonians, crocodilians and tuataras) as of February 2008, five years later in February of 2013 it reports 9,766 species, an increase of 11.9%. Lizard species increased by 14.1% and snake species increased by 8.9% during the five year period. In May of 2011 a graph of the number of snakes described each year since 1758 was posted on this blog and became the fourth most viewed item on this site. Given that interest and my own I decided to take a second look at the issue, in part this was prompted by some recent publications.
Predictions are always tricky because they are based on certain assumptions, and more likely than not, at least some of those assumption are just wrong. Species concepts are changing what is considered a species today would have not been considered a species in 1950. But the change in thinking is for the better, species concepts are now based upon ancestry rather than just morpho-types.

An excellent example of one species name covering many is Brachyorrhos albus, (Moluccan short-tailed snake) a medium sized, fangless, terrestrial homalopsid of eastern Indonesia. What George A. Boulenger, in his Catalogue of Snakes in the British Museum, published 120 years ago, considered Brachyorrhos albus has actually turned out to be three distinct genera and more than nine distinct species. Note that it is more than nine species because there are several yet undescribed species that are known. While it might be best to think about these species as cryptic, only the snakes in the genus Brachyorrhos are cryptic – a group of island species, with each island or group of islands having one or more species that are very similar in appearance. The other two genera are also island species, but are present on large islands (Sumatra and New Guinea and its satellites). Even superficial examination of Calamophis and a soon to be described genus suggest they are morphologically distinct from Brachyorrhos and it is difficult to consider these cryptic in the sense that they don’t look like Brachyorrhos – at all. So, one genus considered monotypic until 2012 was really three genera containing 9+ species. Possibly, just an anomaly.
Representatives of three different genera of 
snakes that were considered a single species 
until 2012.  Middle species is Brachyorrhos 
rafrayi, and bottom is Calamophis
ruuddelangi. JCM

But, how many more anomalies are there? My suspicion is quite a few. Table 1 lists eight genera found to contain cryptic squamates species in the first half of 2013. Note, that Lemme et al. suggest there are at least six lineages within Geckolepis, so the number of undescribed species in this genus is not just a single species. Also, Graham Reynolds et al. (2013) resurrect the genus Chilabothrus for the West Indian members of the boid genus Epicrates and suggest there is an unrecognized species in one of the best known regions of the planet and in a family of snakes that has been particularly well studied in terms of its taxonomy. Also remarkable is the discovery that the Italian “slow worm” Anguis is quite distinct from Anguis fragilis, the species with which it has been long confused.

Table 1. Squamate genera containing species considered cryptic described in the first half of 2013.

Genus
Geography
Reference
Ameiva (Teiidae)
Brazil
Giugliano et al 2013
Anguis (Anguidae)
Italy
Václav et al. 2013
Atractus (Colubridae)
Brazil
Passos et al. 2013
Chilabothrus (Boidae)
West Indies
Graham Reynolds et al. 2013
Cyrtodactylus (Gekkonidae)
Thailand
Pauwels et al. 2013
Geckolepis (Gekkonidae)
Madagascar
Lemme et al. 2013
Helicops (Colubridae)
Brazil
Kawashita-Ribeiro et al. 2013
Stenocercus (Iguanidae)
Ecuador
Torres-Carvajal & Mafia-Endara, 2013

So, it is clear there are many species of squamate reptiles left to be described – all of the evidence says so. But there is a bigger problem – how many species of organisms are there and how rapidly are we causing them to become extinct?
In a 2011 paper by Camilo Mora of University of Hawaii at Manoa and colleagues presented a graph that suggests the number of reptiles (mostly squamates) left to be described  is about 30% of known species – producing a total number of squamates at about 12,615 (my math, not theirs). 

They could be correct – but the actual number of undescribed squamates will prove much greater: the reason – cryptic and fossorial species. Cryptic species seem abundant, overlooked, and disregarded while fossorial squamates are extremely difficult to access.  A Google Scholar search for the words “cryptic species” for the first five months of 2013 returns 4980 papers on virtually all groups of organisms. Restrict the search to “cryptic species reptiles” and the number of returns goes to 550 (~110 papers per month, or about 3.6 papers per day).

Mora et al. (2011) note the total number of species is based on the opinion of taxonomic experts, and note estimates range between 3 and 100 million species for life forms on Earth. They comment that these numbers likely represent the extremes of estimated species. There appears to be about 1.2 to 1.9 million names applied to species, Mora et al. use the lower number. Current description rates of eukaryote species in the last 20 years is about 6,200 species per year, the average number of new species described per taxonomist's career (~24.8 species), and the estimated average cost to describe a new species of animal is about US$48,500 per species (this seems exceptionally high to me but it works out to about $1.2 million/taxonomist during their career). They note that if these values remain constant and are similar among taxonomic groups, describing Earth's remaining species may take 1,200 years, would require 303,000 taxonomists, and cost about US$364 billion. 

Extinction rates now exceed natural background rates by a factor of 100 to 1,000 and raise the issue of species becoming extinct before we know they even exist. Using Mora et al.’s estimated number of 8.7 million eukaryotic species on the planet, and their estimate of about 1.2 million names, 13.8% of Earth’s life forms have been described. 

Now we come to a new view point, Costello et al. (2013) suggest there is no evidence that extinction rates are as high as some have feared, Nigel Stork (one of the authors was quoted as saying, "Surprisingly, few species have gone extinct, to our knowledge. Of course, there will have been some species which have disappeared without being recorded, but not many we think." Professor Stork said part of the problem is that there is an inflated sense of just how many animals exist and therefore how big the task is to record them. "Modern estimates of the number of eukaryotic species have ranged up to 100 million, but we have estimated that there are around 5 million species on the planet (plus or minus 3 million)." And, Stork claims there are more scientists than ever working on the task. This is contrary to the common belief that we are losing taxonomists, the scientists who identify species. He was quoted as saying, "While this is the case in the developed world where governments are reducing funding, in developing nations the number of taxonomists is actually on the rise.”

With the new number of estimated species set at five million, ±3 million we could be very close to having named all of the species. And, with the extinction rates low – clearly we have nothing to be concerned about. Right?

While the number of taxonomists may be on the rise in the Third World, so is the number of people on the planet – sometime during 2012 we exceeded 7 billion Homo sapiens who insist on grinding up one ecosystem after another to support our unsustainable population. The Costello paper has been criticized for its methodology of using well studied groups of organisms to make predictions about poorly studied groups, with one reviewer pointing out they are measuring human activity – not the number of species in nature.

The paper is unfortunate because it serves only to confuse the issues of biodiversity and extinction, and you really have to wonder what those guys were smoking!

References
Costello MJ, May RM, Stork NE. 2013. Can We Name Earth's Species Before They Go Extinct? Science, 2013; 339 (6118): 413 DOI: 10.1126/science.1230318

Giugliano LG, Nogueira C, Valdujo PH, Collevatti, RG, Colli GR 2013. Cryptic diversity in South American Teiinae (Squamata, Teiidae) lizards. Zoologica Scripta,  early online

Graham Reynolds, R, Niemiller ML, Hedges SB, Dornburg A, Puente-Rolón AR, Revell LJ, 2013. Molecular phylogeny and historical biogeography of West Indian boid snakes (Chilabothrus). Molecular Phylogenetics and Evolution, Available online 10 May 2013, ISSN 1055-7903, 10.1016/j.ympev.2013.04.029.

Kawashita-Ribeiro RA, Ávila RW, and Morais DH. 2013. A New Snake of the Genus Helicops Wagler, 1830 (Dipsadidae, Xenodontinae) from Brazil. Herpetologica 69: 80-90.

Lemme I, Erbacher M, Kaffenberger N, Vences M, Kohler J. 2013. Molecules and morphology suggest cryptic species diversity and overall complex taxonomy of fish scale geckos, genus Geckolepis. Organisms, Diversity & Evolution 13:87-95.

Mora C, Tittensor DP, Adl S, Simpson AGB, Worm B 2011. How Many Species Are There on Earth and in the Ocean? PLoS Biology 9(8): e1001127. doi:10.1371/journal.pbio.1001127

Passos P, Junior MTA,  Recoder RS, Sena MA de, Vechio FD, Pinto H B de A., Mendonça SHST, Cassimiro, J, & Rodrigues MT. 2013. A new species of Atractus (Serpentes: Dipsadidae) from Serra do Cipó, Espinhaço Range, Southeastern Brazil, with proposition of a new species group to the genus. Papéis Avulsos de Zoologia 53(6), 75-85. 

Pauwels, OSG, Sumontha M, Latinne A, Grismer L. 2013. Cyrtodactylus sanook (Squamata: Gekkonidae), a new cave-dwelling gecko from Chumphon Province, southern Thailand. Zootaxa 3635 (3): 275–285.

Torres-Carvajal O, Mafia-Endara P. 2013. A new cryptic species of Stenocercus (Squamata: Iguanidae) from the Andes of Ecuador. Journal of Herpetology 47:184-190


Václav G,  Benkovský N,  Crottini A, Bellati A, Moravec J, Romano A, Sacchi R, Jandzik D. 2013, An ancient lineage of slow worms, genus Anguis (Squamata: Anguidae), survived in the Italian Peninsula. Molecular Phylogenetics and Evolution, Available online 20 May 2013, ISSN 1055-7903, 10.1016/j.ympev.2013.05.004.

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