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.
