Australian Biological Resources Study
A.D.Chapman
Australian Biodiversity Information Services, Toowoomba, Australia
A Report for the Department of the Environment and Heritage, September 2005
ISBN (printed) 978 0 642 56849 6
ISBN (online) 978 0 642 56850 2
The number of known species has been estimated by collating information from systematists, taxonomic literature, on-line resources and previous compilations. Although many scientific names are synonyms (thus there being more than one name applied to a species) the numbers of valid species for well-reviewed and familiar groups can be calculated with reasonable accuracy (Groombridge and Jenkins 2002). Most recent calculations for the total number of known (i.e. described) species in the world suggest a figure of around 1.75 million (Hawksworth and Kalin-Arroyo 1995), varying from about 1.5 million to 1.8 million (Tangley 1997).
For less well known groups, the total number of species is much more difficult to estimate, and any estimate will inevitably involve a high degree of uncertainty (Hammond 1992). In taxonomic groups where individuals are generally large, charismatic, easily visible, of economic importance, of public interest, or subject to extensive taxonomic interest, such as mammals, birds, and some higher plant groups, the total number of species is likely to be fairly close to the known or described number of species. On average, around 25 mammal species and five bird species have been described each year over recent times (Hammond 1992), with many of these new species resulting from changes in taxonomic opinion and splitting and not due to the discovery of new species (Groombridge and Jenkins 2002). Estimates for the total number of species on earth varies from 3–5 million (Tangley 1997) to 14 million (Groombridge and Jenkins 2002) and even to as many as 100 million by some (Tangley 1997).
In contrast, for groups of organisms that contain individuals that are small, difficult to collect, obscure, or of no direct public or economic interest (such as many invertebrate taxa), the total number of species is difficult to estimate and is likely to be much much higher than the known number of described individuals (Groombridge and Jenkins 2002). Many of these taxonomic groups have very few or no specialist systematists working on them. In many cases there are undescribed species already in museum collections, but with no systematists available to characterise and describe them. In addition, new molecular techniques applied to some groups, and especially to microorganisms, are discovering new diversity and adding considerably to estimates of the number of species.
Reliable estimates of the total number of species in many of these taxonomic groups are unlikely to be made for many decades, although several new initiatives are attempting to fill the gaps in knowledge. In 1998, the Convention on Biological Diversity established the Global Taxonomy Initiative (GTI) (ABRS 1998, CBD 2005) to try to improve taxonomic knowledge through increasing the number of taxonomists and trained curators, etc. The Global Biodiversity Information Facility (GBIF)1 is attempting to collate, through collaboration, existing attempts to document the names of species of biodiversity through its ECAT program (GBIF 2005a), and through the identification and funding of nomenclatural and taxonomic gaps (GBIF 2005b). Other major projects that are looking at documenting names and taxa on a global basis are the Species 20002 project and the Integrated Taxonomic Information System (ITIS)3 project which combine to produce the annual Catalogue of Life CDs (Bisby et al. 2005), and the International Plant Names Index (IPNI).4
When it comes to Bacteria and the Archaea, trying to estimate the number of species (both known and total) is compounded by the difficulty in determining what delimits a ‘species’. Generally, species are determined based on features shown in culture (Woese 1998, Ward 2002), and any estimate of the total number of species in the world is just about impossible to make. Indeed, according to Curtis et al. (2002) ‘The absolute diversity of prokaryotes is widely held to be unknown and unknowable at any scale in any environment.’
The listing of threatened species is not an easy matter. All lists lag well behind discovery and taxonomic revision, and thus are likely to provide under-estimates. Also, on a world basis, very few countries list undescribed species, and this again leads to under-estimation. The only lists available that are regularly updated on a world basis are the Red Lists of Threatened Species (IUCN 2004) produced by the IUCN Species Survival Commission and, even though these include considerable error (Kirschner and Kaplin 2002), I have relied on them for numbers of threatened species for the world.
Similarly, listing of threatened species in Australia is not simple. As well as the list of nationally threatened species maintained by the Australian Government (DEH 2005a, b), each State also maintains a list for that State. The national list contains errors, and is always well behind discovery, taxonomic revision and often State listings, however it is the only comprehensive list of ‘nationally’ threatened species that is available. The national list has been used in this report.
State lists also contain errors, with some States listing species threatened in that State, but which may be common across the border in another State, and some lists are not consistently maintained and updated on a regular basis. Some States (e.g. Western Australia) also list species under categories additional to those recognised by the IUCN. Although these species may be of no less importance for regional conservation, they are not listed here as it is difficult to provide comparisons between the State lists and between the State lists and the National list. It is hoped that the development of the Australia’s Virtual Herbarium (AVH)5 and Online Zoological Collections of Australian Museums (OZCAM)6 will lead to a more consistent approach to the development of both State and Commonwealth lists of threatened species.