Each of the checklists is based on a single taxonomic source that covers all species in a group on a global basis.  For the sake of consistency, each of these taxonomic sources is used as the final authority on the validity of species regardless of subsequent taxonomic changes or new discoveries.  Although all of these sources also included some information on distribution, all required checking additional sources to confirm ranges.  Islands or island groups divided into more than one political unit (such as Borneo, Hispaniola, the Solomons, and the Comoros) almost invariably required such checking.  

In addition to the checklists based on a single global taxonomic source, a few national checklists provided by an expert on a group are also provided.  See for example the one on the Reptiles of Pakistan (here).

An endemic species for the purposes of the checklists is considered to be one that currently occurs as a breeding species in a single political unit (for example New Caledonia or South Sudan).  Formerly more widespread species that currently survive in only a single country are also considered endemic (for example the Hirola in Kenya).  Species that have been introduced to other countries are also considered endemic to their original country of origin (for example South Africa's Bird of Paradise Flower).  The situation is more complex for the handful of species in which reintroduction attempts are being made into their former range.  For example, the Crested Ibis was included in the checklist as endemic to China until reintroduced birds in Japan successfully bred in 2012.  Species known from border regions and frequently assumed to occur also in similar habitats in a neighboring nation are treated as endemic unless a definite record exists for the second country.  In cases of doubt species are usually included as an endemic. Recently extinct species (such as the Golden Toad in Costa Rica) are included in the lists if they were included in the taxonomic source, both because they may be indicators of areas that may include other endemic species and because some "extinct" species have turned out to be not quite as extinct as had been previously assumed (for example Jerdon's Courser in India).


How accurate are the checklists?

It is safest to assume that most of the longer checklists (and many of the shorter ones) can be improved upon.  Although for some island nations the checklists may accurately reflect current knowledge, for many mainland nations the situation is quite a bit messier.  In a number of cases, a species will be included as an endemic because an inadequate search of the literature by the compiler failed to discover records from other countries.  One complicating factor is a lack of consensus on species boundaries that can result in misidentifications in the literature or differing usages of the same scientific name to mean different things.  For example the name Leopardus colocolo is most commonly used to refer to a cat found in a number of countries (IUCN Red List), but is used by the mammal source in a more narrow sense to refer to a population occuring only in Chile (Mammal Species of the World).  A number of species may have been inadvertantly omitted from the list by the compiler not realizing that a name was being used in a different sense.

It is also important to remember how much is still unknown to science.  Thousands of vertebrate species, tens of thousands of vascular plant species, and millions of invertebrate species still await discovery and scientific description.  For example, according to the State of Observed Species report 19,232 new species were described in 2009 (IISE pdf file).  Over 6600 new species of fish have been described since 1992 (Catalog of Fishes).  Some parts of the world are also much more poorly known than others - for example only one of the 93 freshwater fish species known solely from Laos had even been described before 1995.  A sizeable majority of the species newly described are known from only a single nation.  158 out of 168 (94.0 %) reptile species described in 2007 (according to Reptile Database accessed 22 February 2009) and 171 out of 180 (95.0 %) amphibian species described in 2007 (according to Amphibian Species of the World accessed 23 February 2009) are so far known exclusively from a single country.


Political Units

Countries and dependent areas are those recognized by the CIA World Factbook (CIA).  Additional accounts appear for species of Unknown Origin, those found solely in International Waters, those unique to the Korean Peninsula, and those restricted to the island of Timor.  The Cyprus account includes the nation of Cyprus plus the United Kingdom administered areas of Akrotiri and Dhekelia.  Israel, the West Bank, and the Gaza Strip are discussed jointly for practical reasons.

Lists of endemic mammals, birds, reptiles, and amphibians based on biological regions rather than political ones are also available on the Web.  For terrestrial ecoregions see WWF's Wildfinder (WWF) and for biodiversity hotspots see the Terrestrial Species Vertebrate Search at (CI).


Country Overview Pages

These pages provide introductions to the wealth of resources on the web dealing with the world's animal and plant species.  It also allows for the mention of endemic invertebrate and vascular plant species plus additional vertebrate species that are recognized by some authorities or were described since the sources used for the checklists.  Countries and dependent areas lacking known endemic species are not given a country overview page.


Mammals

Wilson, D.E. & Reeder, D.M. (Eds.)(2005) Mammal Species of the World: A Taxonomic and Geographic Reference.  Third Edition.  The Johns Hopkins University Press, Baltimore.

An online version of the above work can be found here.

Wilson & Reeder recognized 5416 mammal species of which 2284 species (42.2 %) are single nation endemics.  158 additional mammal species unique to a single nation described too recently to be included in Wilson and Reeder are included as addenda in the appropriate national checklists.  274 of 1229 (22.3 %) mammal genera are also restricted to a single country.  Extinct species are included in Wilson & Reeder if they were possibly alive in the previous 500 years.  An international assessment of the world's mammal species that appeared after the mammal checklists had been completed provides detailed distribution information including maps of all the world's mammals (IUCN Red List).  For recently discovered mammal species see (Wikipedia), (Planet' Mammiferes), and (PNAS pdf file).  For a list of mammal species described in 2012 see (Planet' Mammiferes).


Birds

Dickinson, E.C. (Ed.)(2003) The Howard and Moore Complete Checklist of the Birds of the World.  Revised and enlarged third edition.  Princeton University Press, Princeton.

Dickinson recognized 9721 bird species of which 2597 (26.7 %) are single nation endemics.  34 additional bird species unique to a single nation described too recently to be included in Dickinson are included as addenda in the appropriate national checklists.  331 of 2161 (15.3 %) bird genera are also restricted to a single country. An independent assessment of single nation endemics using the above reference can be found at Avibase (Avibase) which also provides assessments based on several other authorities as well.  An especially detailed source of distributional information for all the world's birds can be found at BirdLife International (BirdLife Int'l).  For recently described bird species see (Wikipedia).


Reptiles

The EMBL Reptile Database CD September 2001 edition. Updated with changes through 2004 making it current to January 2005 (see Reptile Database).  The current online version of the Reptile Database can be found here.

The January 2005 version of the EMBL Reptile Database recognized 8240 reptiles species of which 4810 (58.4 %) are single nation endemics.  499 additional reptile species unique to a single nation described too recently to be included in the January 2005 EMBL Reptile Database are included as addenda in the appropriate national checklists.  293 of 1029 (28.5 %) reptile genera are also restricted to a single country.  For lists of recently described reptile species search by year and location at (Reptile Database).


Amphibians

Frost, D.R. (2004) Amphibian Species of the World: an Online Reference. 3.0 (22 August 2004).  American Museum of Natural History, New York, USA.  (see here). The current online version can be found here.

The August 2004 version of Frost recognized 5700 species of which 3838 (67.3 %) are single nation endemics.  834 additional amphibian species unique to a single nation recognized too recently to be included in the August 2004 version of Frost are included as addenda in the appropriate national checklists.  151 out of 445 (33.9 %) amphibian genera are also restricted to a single country.  An international assessment of the world's amphibian species that appeared as the amphibian checklists were nearing completion provides detailed distribution information including maps of all the world's amphibians (IUCN Red List).  A summary of single nation amphibian endemism from this assessment can be found here.  A subsequent publication, "The Amphibian Tree of Life" (AMNH 9 MB pdf file), has resulted in major changes to amphibian taxonomy above the species level.  For lists of recently described amphibian species search by year of publication and country at (Amphibian Species of the World) or see the new species page at AmphibiaWeb (AmphibiaWeb).


Fishes
FishBase 2004: a global information system on fishes. DVD. WorldFish Center - Philippine Office, Los Banos, Philippines.  Published in May 2004.  The current online version of this database can be found here.

14735 species of fish are found in freshwater or brackish habitats of which 7593 (51.5 %) are single nation endemics.  1668 additional freshwater fish species unique to a single nation added too recently to be included in FishBase 2004 are included as addenda in the appropriate national checklists.  The marine fish checklists include only species that occur mainly in habitats between 0 and 200 m deep and therefore do not include bathypelagic and bathydemersal species.  For recently described fish species see (worldfish.de) and search by year and location at (Catalog of Fishes) or by year at (FishBase).

Fish species for which distributional records suggest they have been recorded from a single country, but for which a FishBase occurrence record suggests that specimens may exist from an additional country are listed with a special notation (OC).  It is obvious that some of these records are erroneous - a number are from the wrong continent or are obviously misidentifications.  However many would appear to be valid and it appears this is connected with geography.  For example, it seems to the compiler that all the U.S. freshwater species tagged with an OC notation are in fact restricted to the U.S. as naturally occurring species while the list for the Democratic Republic of the Congo probably includes many species that have in fact been collected in neighboring countries.

Vertebrate Genera

The sources for the vertebrate genera are the same as those for species.  However some genera have been excluded as being endemic based on the ranges of subsequently described or undescribed species.  1868 out of 9990 (18.7%) vertebrate genera are single nation endemics.  35 additional recently described vertebrate genera unique to a single nation are included as addenda in the appropriate national checklists.


Swallowtail & Milkweed Butterflies

Collins, N.M. & M.G. Morris (1985) Threatened Swallowtail Butterflies of the World: The IUCN Red Data Book.

Ackery, P.R. & R.J. Vane-Wright (1984) Milkweed Butterflies.  Cornell University Press,  Ithaca, NY.

These two groups have been selected as examples of invertebrate endemism although both lists are somewhat dated in their taxonomy compared to the vertebrate checklists.  245 out of 753 (32.5 %) of these two butterfly groups are single nation endemics.  A more current checklist of the world's swallowtail butterflies can be found at the Global Butterfly Information System (GloBIS).  National checklists at the species level are available for a number of other invertebrate groups through the Catalogue of Life using the search by distribution feature (Catalogue of Life).


Vascular Plant Genera

Mabberley, D.J. (2008) Mabberley's Plant-book. Third Edition. Cambridge University Press, Cambridge.

Mabberley recognized 13313 vascular plant genera of which 3422 (25.7 %) are single nation endemics.  Note that it is also possible to create global species checklists with distributional information for many plant families using the "Build a Checklist" feature at the World Checklist of Selected Plant Families website (Kew). Recently described species can be found using the search function at the International Plant Names Index (IPNI).


Families & Orders

The sources for the vertebrates and vascular plants are the same as given above. For invertebrates (protozoans are excluded) the source is:

Parker, S.P. (Ed.)(1982) Synopsis and Classification of Living Organisms. 2 Vols. McGraw-Hill, New York.

Out of 5810 families (990 vertebrates, 4360 invertebrates, and 460 vascular plants), 265 (4.6 %) are single nation endemics.