The magnificent Iberian Lynx Lynx pardinus (Critically Endangered) found in Portugal and Spain, may be the first wild cat species to go extinct in recent times, if habitat loss, persecution, and loss of its main food source continues.
Photo: © WWF-UK.
The 2000 update of the IUCN Red List (Hilton-Taylor 2000) included global conservation assessments for 16,507 species, 11,406 of which were listed as threatened. Since 2000, the taxonomic coverage of the IUCN Red List has substantially increased (for further details on the taxonomic expansion, see description of the Red List Programme in Appendix 1). In addition, there has been a concerted effort to record and document Least Concern species (i.e., species with low extinction risk). Appendix 2a provides a summary of the IUCN Red List Categories and Criteria (IUCN 2001).
The 2004 update of the IUCN Red List includes assessments for 38,047 species:
15,589 are threatened with extinction (listed as Critically Endangered, Endangered or Vulnerable),
844 are Extinct or Extinct in the Wild,
3,700 are listed as Near Threatened or Conservation Dependent,
3,580 are Data Deficient, and
14,334 are Least Concern.
In addition to the species level assessments, the 2004 IUCN Red List also includes 2,140 assessments of infraspecific taxa (i.e., taxa below the level of a species) or discrete subpopulations, of which 1,383 are listed as threatened. In total, assessments for 40,187 taxa are included on the 2004 IUCN Red List of Threatened Species™ thus enhancing the reputation of the IUCN Red List as the most comprehensive assessment of the status of the world's ‘species’.
The 15,589 species threatened with extinction, although only just over one per cent of the world's described species, includes 12% of all bird species, 23% of all mammal species, 32% of all amphibian species and 34% of all gymnosperms (mainly conifers and cycads). In other words, one in every eight birds, one in every four mammals, and one in every three amphibians and gymnosperms is facing a high to extremely high risk of extinction in the near future (see Table 2.1).
Although the number of species assessed has increased substantially in recent updates of the IUCN Red List, the conservation status of most of the world's species remains poorly known. Only a very small proportion (2.5%) of the world's described species have been evaluated for the IUCN Red List (see Table 2.1), and there is a strong bias in this sample towards terrestrial vertebrates and plants and in particular to those species found in biologically well-studied parts of the world.
The true proportion of species evaluated is certainly higher than the figures given in Table 2.1 because of the under-reporting of Least Concern assessments. This problem is being addressed by the Red List Programme (see Appendix 1).
The proportion of species evaluated is further confounded by the increasing numbers of species being described in the major taxonomic groups (see Box 2.1). There is also considerable uncertainty about how many of the published names are accepted and how many are synonyms.
For most of the major taxonomic groups, the discovery of entirely new species contributes significantly to the increases in species numbers. However, for birds, the discovery of new species is now rare, a recent exception being the discovery of a new flightless rail, the Calayan Rail Gallirallus calayanensis, on a remote island in the Philippines (the status of this has not yet been evaluated). The discovery of new species of large mammals is also now very unusual, but there are exceptions, most notably the discovery of the Soala Pseudoryx nghetinensis and the Giant Muntjac Deer Muntiacus vuquangensis in Viet Nam in the 1990s. A number of ‘cryptic’ new mammal species are also being discovered through the resolution of species complexes using new molecular or advanced morphological techniques. However, many of the changes in mammal species numbers are due to subspecies being raised to species as a result of a change in species concept (i.e., a shift from the biological species concept to the phylogenetic species concept), a phenomenon that has been termed ‘taxonomic inflation’ (Isaac et al. 2004). There are currently a number of mammal subspecies included on the IUCN Red List, which may be treated as full species in the third edition of Mammal Species of the World (Wilson and Reeder in press), and so the true number of mammal species evaluated is probably higher than the 4,853 indicated in Table 2.1.
Table 2.1 Numbers of threatened species by major taxonomic group
(See Appendix 2b for details on sources of numbers of described species and Appendix 3a for changes in the numbers of threatened species since 1996)
The lack of stability in the numbers of described species, and the high degree of uncertainty surrounding some of the numbers, need to be borne in mind when examining the results for what has been evaluated. Figure 2.1 shows the proportion of species evaluated in all the major taxonomic groups.
The Saola Pseudoryx nghetinhensis (Endangered) is generally considered to be the greatest mammal discovery in recent times, and is so different from any currently known species that a separate genus had to be created. It was only ‘discovered’ by western science in 1992 and described in 1993. Occurs in Lao PDR and Viet Nam.
Photo: © WWF-Canon / David Hulse.
The vertebrates (Figure 2.1a) are the best evaluated group, with almost 40% of the species recorded on the IUCN Red List, while the plants and invertebrates are poorly evaluated by comparison. Within the vertebrates, the birds and amphibians are fully evaluated (Figure 2.1b) (though the analysis excludes a few new amphibian species that were described in 2004 after the completion of the Global Amphibian Assessment project, e.g. Phyllodactylus punctatus, Philautus petilus, Tomopterna luganga, etc.), while the number of mammals evaluated has declined from 100% in 1996 (Baillie and Groombridge 1996) to almost 90%. This decline is because of the increasing number of described mammal species (but see the discussion above about ‘taxonomic inflation’). Reptiles and fishes are currently poorly represented on the IUCN Red List, but plans are in place to address this (see Appendix 1).
For the invertebrate groups (Figure 2.1c), relatively few species have been evaluated, and the evaluations that have been done have tended to focus on molluscs (particularly freshwater and terrestrial species) and on crustaceans (primarily inland water crustaceans). Among the insects, the only groups that have received noteworthy attention are the swallowtail butterflies (Papilionidae) and the dragonflies and damselflies (Odonata). The other invertebrates are very poorly represented on the IUCN Red List, but the following phyla are represented at least by a few species: Annelida (segmented worms); Cnidaria (e.g., sea anemones); Echinodermata (e.g., sea urchins, starfish, etc.); Nemertinia (unsegmented worms); Onychophora (velvet worms); and Platyhelminths (flatworms). There are other significant invertebrate groups (in terms of species numbers and their role in ecosystem function) that are not yet represented on the IUCN Red List such as the Porifera (sponges) and the Nematoda (roundworms). There are plans to increase the number of invertebrate evaluations particularly for freshwater dependent taxa (see Appendix 1).
Figure 2.1 The percentage of species evaluated in each major taxonomic group.
Although almost 12,000 species of plants are now recorded on the IUCN Red List, this represents only 4% of the world's plant diversity. The species evaluated now include representatives from all the major plant taxonomic groups. But the only major plant group almost fully evaluated is the gymnosperms (conifers and cycads; Figure 2.1d). In considering plants it is also important to note the 33,798 species listed as threatened in the 1997 IUCN Red List of Threatened Plants (Walter and Gillett 1998). This work in effect remains a companion Red List that should be used in conjunction with the annual updates of the IUCN Red List of Threatened Species™, until such time as all taxa in the 1997 Plants Red List have been reassessed under the 2001 IUCN Red List Categories and Criteria (IUCN 2001; see further discussion under section 2.4 below).
In addition to the taxonomic groups discussed above, the IUCN Red List also includes representatives from two other Kingdoms. The Protista (comprising approximately 80,000 described species) are represented by one Extinct species of red alga (a seaweed from Australia), while the Fungi (comprising approximately 72,000 described species) are represented by only two threatened species of lichen (numbers of described species from Hammond 1995) (see Section 2.5).
Despite the relatively low number of species evaluated and the biases towards the better known taxonomic groups, the 2004 IUCN Red List provides clear evidence that there is cause for conservation concern (see Sections 2.3 and 2.4 and Section 4), and it is likely that the situation is similar for taxonomic groups not yet evaluated.
The 2004 IUCN Red List includes 7,266 animal species threatened with extinction compared to 5,435 in 2000 (see Tables 2.1 and 2.2 and Appendix 3a). Comparing the numbers of threatened species in the major taxonomic groups reported for the 2000 and 2004 updates of the Red List (see Appendices 3a and 3b), it is clear that the overall number of threatened species has increased in all groups, with the exception of the mammals (see details below). Most of the increase in numbers of threatened animals is due to the incorporation of assessments for all amphibian species for the first time (the number of threatened amphibians increased from 146 in 2000 to 1,856). Although there are more threatened species, the proportions of each taxonomic group threatened, with the exception of that for the amphibians, has remained much the same as in 2000. This is because the increases have been either relatively small (e.g., for the reptiles a net gain of 10 threatened species) or they have been offset by increases in the number of described species (e.g., for fishes a net gain of 48 threatened species and a gain of 3,500 described species). The birds are the only taxonomic group for which since 2000 there has been a decrease in the number of recognized species (9,946 to 9,917) and an increase in the number threatened (1,130 to 1,213). In most cases these ‘apparent’ increases in numbers of threatened species are not genuine deteriorations in status, but the result of better knowledge or changes in taxonomy. Any extrapolation of trends from the numbers of threatened species in 2000 versus 2004 should only take into account the genuine changes (see Section 4 for further details).
The IUCN Red List Categories and Criteria (IUCN 2001, p. 7) state that species listed as Data Deficient (DD) “should not be treated as if they were non-threatened”. In reality, many Data Deficient species are likely to be threatened, so we are generally under-estimating levels of threat, particularly in comprehensively assessed groups like the amphibians and mammals with relatively large numbers of DD species (1,290 and 380 respectively). However, a proportion of the DD species are also likely to be listed as Least Concern or even as Extinct once the relevant data become available. How many DD species are threatened and how many are not, is difficult to estimate. In this analysis we take an evidentiary rather than a precautionary approach, and so are under-estimating the levels of threat. Hence the 2,882 animal species listed as DD on the 2004 IUCN Red List are not included in the number considered to be threatened (Table 2.1).
In addition to the species listed as threatened, 2,302 are listed as Near Threatened (NT). This category has no quantitative criteria, and is used for species that come close to meeting the thresholds for a threatened category (see Appendix 2a). The vast majority of Near Threatened animal species are mammals (587) and birds (773). If the numbers in this category were combined with those listed as threatened, then the percentage of birds, mammals and amphibians that are threatened or near threatened would rise to 20%, 35% and 39% respectively (based on numbers of evaluated species).
There is an additional category – LowerRisk/conservation dependent (LR/cd) that was used in an earlier version of the Red List Categories (IUCN 1994a) but has subsequently been dropped (IUCN 2001). This category was used to indicate species that would be listed as threatened were it not for species-specific conservation programmes. There are still 111 animal species listed as LR/cd (Table 2.2), and until such time as these are all re-evaluated, this category will persist as an artefact of the previous classification system. The LR/cd category was rarely used for animals except for mammals, which still have 64 species in this category, 39 of which are hoofed mammals or artiodactyls, and 14 are cetaceans (whales and dolphins) (see Figure 2.2a).
The 1996 IUCN Red List (Baillie and Groombridge 1996) featured complete evaluations for all of the world's bird and mammal species. Since then, the birds have been re-evaluated twice by BirdLife International and its partners (BirdLife International 2000, 2004a). A major advance for 2004 is the inclusion of a third completely evaluated group of vertebrates, namely the amphibians. The amphibians were evaluated as part of the Global Amphibian Assessment (GAA) project that started in 2001 (IUCN, CI and NatureServe 2004). As discussed above in Section 2.2, the number of described mammal species has increased and as a result there are 563 ‘new’ mammal species that have not yet been evaluated. In addition, many of the mammal assessments were done eight years ago and might no longer be a true reflection of the status of the species concerned (3,472 of the mammal species assessments, 737 of which are threatened, date from the 1996 IUCN Red List, but a third of the threatened species have been re-evaluated since 1996). Nevertheless given that almost 90% have been evaluated, the results for mammals can still be compared to those for the birds and the amphibians (see Figures 2.2 a, b, c and Table 2.1).
Table 2.2 Summary of Red List Category classifications by class of animals
The proportions of species in the different Red List Categories differ markedly between these three vertebrate groups. Comparing the threatened categories (CR, EN and VU), 12% of bird species are considered threatened, versus 23% of mammals and 32% of amphibians. The amphibians have more than twice as many species listed as Critically Endangered or Endangered (1,188 in total) than the birds and mammals (see Table 2.2 and Figure 2.2) and are currently the most threatened class of vertebrates on the IUCN Red List. In addition, 12% of mammals, 8% of birds and 6% of amphibians are listed as Near Threatened. The situation for the amphibians may be even worse than the figures indicate, because 23% of them are listed as Data Deficient (i.e., there is inadequate information to assess the extinction risk). Once further information is obtained on these species it is probable that many will be listed in one of the threatened categories or even as Extinct. Mammals are better known than the amphibians, with only 8% listed as Data Deficient, while the birds are extremely well known with only 1% as Data Deficient. It was mentioned in section 2.2 that the mammals were the only group where the number of threatened species had declined. The decline (from 1,130 in 2000 to 1,101 species) is not due to successful conservation actions followed by a genuine recovery. This change is the result of new listings for a number of African rodent species as a result of taxonomic changes and better information and knowledge being made available through the Global Mammal Assessment project (see Appendix 1).
Percentages of extant mammal, bird and amphibian species in each Red List Category. The pie charts exclude the categories Extinct, Extinct in the Wild and Not Evaluated.
The proportion of species considered not threatened also differs markedly with 78% of birds, 56% of mammals and 39% of amphibians being listed as Least Concern. The relatively large numbers of Least Concern bird species is, however, no reason to be complacent as many common bird species are in decline across the world (BirdLife International 2004b).
Figure 2.2 clearly indicates that a large number of mammal, bird and amphibian species are close to extinction, with 27% of the species evaluated listed as globally threatened because they have small and/or rapidly declining populations and/or small ranges. In total, 405 mammal, bird and amphibian species are Critically Endangered and face an extremely high risk of extinction in the immediate future. The prospect of a major extinction event raises questions about which groups of species are most likely to be lost, and which are more susceptible to decline than others. A number of studies in recent years have analysed the IUCN Red List data to determine which orders and families of birds and mammals are most susceptible to extinction (Bennett and Owens 1997; Mace and Balmford 2000; Purvis et al. 2000a). As we now have updated information for all threatened birds and, for the first time, all amphibians, this analysis has been repeated here (see Appendix 2b for details of the methodology and Appendices 3c-h for the detailed results), and the main findings are presented in Figure 2.3 (for mammals), Figure 2.4 (for birds) and Figure 2.5 (for amphibians).
Care is needed in interpreting the results in Figures 2.3 to 2.5. That a given order or family has a significantly lower percentage of threatened or extinct species than average does not mean that it has “low threat”. Indeed, the ‘expected’ levels of threat in the absence of human activities are presumably close to zero, and therefore most taxa are highly threatened in relation to what would be expected in a natural situation. The results in Figures 2.3 to 2.5 are all comparisons in relation to the average situation amongst species in the same group. For example, a family with 33% threatened species is not significantly different from the average threat levels in amphibians but it is very significantly more threatened than the average amongst birds. It should also be noted that the low percentage of threatened and extinct species is in some cases artificially low because of lack of knowledge on the species' threatened status. For example, only two out of 109 species of the amphibian family Caeciliidae are listed as threatened (Figure 2.5), but 66 species are Data Deficient, many of which might turn out to be threatened.
The results in Figure 2.3a (see Appendix 3c for detailed results) show that the Rodentia (rodents) is the only mammalian order with significantly fewer than expected threatened or extinct species, despite having the largest number of threatened mammal species on the Red List. Five orders have significantly more threatened species than would be expected, namely the Sirenia (dugongs and manatees), Perissodactyla (equids, rhinos and tapirs), Artiodactyla (deer, antelope, cattle, sheep, goats, etc.), Primates, and the Carnivora (cats, dogs, weasels, bears, etc.). These results are similar to those found by Mace and Balmford (2000).
The mammalian families that are highlighted as having significantly higher numbers of threatened species than average (Figure 2.3b; see Appendix 3d for detailed results) include the Hominidae (great apes); Tapiridae (tapirs); Nesophontidae (West Indian shrews); Indridae (avahi, sifakas and indri); Equidae (zebras and wild horses); Peramelidae (bandicoots); Lemuridae (lemurs); Chrysochloridae (golden moles); Capromyidae (hutias); Felidae (cats); Cercopithecidae (Old World monkeys); Bovidae (wild cattle, antelope, sheep and goats); and Pteropodidae (fruit bats). Many of these families are the same as those identified by Mace and Balmford (2000), but there are some new additions (e.g., the Felidae and Cercopithecidae). While the results confirm Mace and Balmford's (2000) observation that most of the highly threatened families are species poor, the Bovidae, Cercopithecidae and Pteropodidae are relatively species rich. Some of the differences could be artefacts of the statistical methods used. The major threats to the Bovidae and Cercopithecidae include habitat loss (primarily due to agricultural expansion) and hunting (for food and medicinal purposes), while for the Pteropodidae (a group which is fairly restricted in its geographic range), habitat loss due to extraction of timber, hunting for food, and general human disturbance are the main threats.
The percentage of threatened or extinct mammal species: a) in each mammalian order; and b) in each mammalian family. Each circle corresponds to an order or family, positioned according to the number of species in the order and the percentage of those species that are threatened (Vulnerable, Endangered or Critically Endangered) or extinct (Extinct or Extinct in the Wild). The horizontal dashed line indicates to the percentage of threatened or extinct species among mammals as a whole (24%). Orders or families with higher levels of relative threat are depicted above this line, orders or families with lower levels are represented below. The coloured bands indicate the level to which the percentage of threatened or extinct species in each order or family is significantly different from the average. Orders or families with threat levels that are very significantly different from the average (p <0. 01) are listed individually on the right section of the figure. Values between parentheses indicate number of threatened or extinct species/total number of species (e. g. , 84 out of 281 species of Carnivora are threatened or extinct). For the summary data, see Appendices 3c and 3d.
Photo: © Troy Inman
Photo: © Anna Lushchekina
Photo's 2.3, 2.4, and 2.5 (top to bottom)
Representatives of mammalian families with more threatened species than average include: Western Gorilla Gorilla gorilla (Endangered) from Central Africa; Saiga Antelope Saiga tartarica (Critically Endangered) from Central Asia; and the Comoro Black Flying Fox Pteropus livingstonii (Critically Endangered).
Photo: © Richard Wainwright
The mammalian families identified as having significantly fewer threatened species than expected include the Ziphiidae (beaked whales); Delphinidae (dolphins); Ctenomyidae (tuco-tucos); Heteromyidae (pocket and kangaroo mice); Echimyidae (spiny rats); Sciuridae (squirrels, marmots, prairie dogs); and the Muridae (mice, rats, gerbils). The Delphinidae are generally widely distributed species and as a result although relatively wellknown locally they are very poorly known globally; hence seven subpopulations are listed as threatened on the IUCN Red List, compared to only one species globally, while 20 species are listed as Data Deficient. The level of extinction risk in the Ctenomyidae and Sciuridae might be underestimated because these families are poorly known in terms of their taxonomy and population biology. The Muridae is by far the largest mammalian family and it dominates the mammals in the Red List numerically with 227 threatened and 20 Extinct species. It is possible that the extinction risk for this group has been underestimated because many of the species are poorly known. In addition many apparently widespread murid species might be species complexes, which, once resolved, could result in an increased number of range-restricted species that are under threat. However, many of the murid genera are highly adaptable to habitat loss and have become commensal with people.
A significant finding from this analysis and that of Mace and Balmford (2000) is that in general, most of the threatened orders and families of mammals are species-poor. This, coupled with observations from other groups that threatened higher taxa tend to be phylogenetically unique, strongly suggests that impending extinctions will lead to a disproportionate loss of evolutionary novelty.
Mace and Balmford (2000) found no clear-cut relationships between the percentage of threatened species in a group and either its species richness or its average body mass or body size. Mace and Balmford (2000) suggest that much more detailed analyses of life history traits and extinction risk are required to disentangle the causes and constraints. Some progress in this regard has been made in a recent study of the impacts of human population density on extinction risk in carnivores (Cardillo et al. 2004). They demonstrated that extinction risk in carnivores was more strongly predicted by intrinsic biological traits than exposure to high-density human populations.
Figure 2.4 shows that extinction risk is not distributed evenly, or randomly, across bird orders and families. Certain orders and families contain a large proportion of threatened species, while others contain a smaller proportion than expected. Nine bird orders contained significantly more threatened species than average (Figure 2.4a; see Appendix 3e for detailed results): Apterygiformes (kiwis); Sphenisciformes (penguins); Pelecaniformes (cormorants, pelicans, etc.); Procellariiformes (albatrosses and petrels); Ciconiiformes (storks, ibises and spoonbills); Galliformes (pheasants, partridges, quails, etc.); Gruiformes (cranes, bustards, rails, etc.); Columbiformes (doves and pigeons); and the Psittaciformes (parrots). The Piciformes (woodpeckers, toucans, barbets, etc.); Apodiformes (swifts and hummingbirds); and Passeriformes (songbirds) are the orders with significantly fewer threatened species than average (Figure 2.4a).
There are 15 extinction prone families (Figure 2.4b; see Appendix 3f for detailed results): the Mesitornithidae (mesites); Apterygidae (kiwis); Gruidae (cranes); Spheniscidae (penguins); Megapodiidae (megapodes); Diomedeidae (albatrosses); Drepanididae (Hawaiian honeycreepers); Phalcrocoracidae (cormorants); Cracidae (cracids); Procellariidae (petrels); Zosteropidae (whiteeyes); Rallidae (rails); Phasianidae (pheasants, partridges, etc.); Columbidae (doves and pigeons); and Psittacidae (parrots). Ten families contain significantly fewer than expected threatened species: Bucconidae (puffbirds); Dendrocolaptidae (woodcreepers); Paridae (tits); Capitonidae (barbets); Nectariniidae (sunbirds); Picidae (woodpeckers); Trochilidae (hummingbirds; Tyrannidae (tyrant flycatchers); Emberizidae (buntings); and the Muscicapidae (thrushes, warblers and flycatchers).
The results generally match those reported by Bennett and Owens (1997) as all eight families identified by them as having significantly more threatened species appear here again as do many of the other families with unusually high numbers of threatened species. Differences in the results obtained by Bennett and Owens (1997) and those shown in Figure 2.4 can largely be explained by the different classification systems used for the families. For example, the Hawaiian honeycreepers are treated here as a distinct family separate from the Fringillidae, and have significantly more threatened species than expected with 31 out of 34 listed as threatened. The situation in this family is symptomatic of the levels of habitat loss and the impacts of invasive species on the native fauna and flora of Hawaii. The cormorants, however, are a new addition to the list of families with more threatened species than expected because four additional species have now been added to the Red List. Three of the additions were due to improved knowledge, but in the case of the Bank Cormorant Phalacrocorax neglectus, there has been a genuine deterioration in status as a result of human disturbance, competition with seals for breeding sites, a decreasing food supply and the impacts of oil spills. Among the most threatened families are those that suffer particularly from exploitation for food (megapodes, pheasants, pigeons) or as pets (parrots).
Photo: © Ferne McKenzie
Photo: © Troy Inman
Photo's 2.6, 2.7, and 2.8 (top to bottom)
Representatives of avian families with more threatened species than average include: Brown Kiwi Apteryx mantelli (Endangered) from New Zealand; Waved Albatross Phoebastria irrorata (Vulnerable) from the Galápagos, Ecuador; and the ‘Akiapola’au Hemignathus munroi (Endangered) a honeycreeper from Hawaii.
Photo: © Jack Jeffrey Photography
The percentage of threatened or extinct bird species: a) in each avian order; and b) in each avian family. Each circle corresponds to an order or family, positioned according to the number of species in the order and the percentage of those species that are threatened (Vulnerable, Endangered or Critically Endangered) or extinct (Extinct or Extinct in the Wild). The horizontal dashed line indicates to the percentage of threatened or extinct species among birds as a whole (12%). Orders or families with higher levels of relative threat are depicted above this line, orders or families with lower levels are represented below. The coloured bands indicate the level to which the percentage of threatened or extinct species in each order or family is significantly different from the average. Orders or families with threat levels that are very significantly different from the average (p <0. 01) are listed individually on the right section of the figure. Values between parentheses indicate number of threatened or extinct species/total number of species (e. g. , 16 out of 51 species of the family Cracidae are threatened or extinct). For the summary data, see Appendices 3e and 3f.
The analysis by Bennett and Owens (1997) further showed that increased extinction risk is associated with increases in body size and low fecundity rates and it is suggested that the evolution of low fecundity many millions of years ago predisposed certain lineages to extinction. Purvis et al. (2000) have also shown that bird extinctions are phylogenetically non-random. While some of the orders and families that are more threatened than expected have relatively few species (e.g., the mesites and kiwis), many are relatively species rich (e.g., the parrots). In other words, we stand to loose not only unique phylogenetic lineages, but also lineages of large and charismatic groups.
The analysis of amphibian orders (Figure 2.5a; see Appendix 3g for detailed results) is not particularly informative as there are only three orders. The results indicate that the Gymnophiona (caecilians, or limbless amphibians) are significantly less threatened than average (only two threatened out of 168 species), but this is misleading because 111 of the species are listed as Data Deficient. With better information these species could prove to be as threatened as the average for amphibians. The Caudata (salamanders and newts) have significantly more threatened species than average, as the species tend to have small ranges and are very sensitive to habitat loss. The average number of threatened species is determined by the Anurans (frogs and toads), by far the largest amphibian group with over 5,000 species.
The results of the family level analysis are much more informative (see Figure 2.5b; see Appendix 3h for detailed results). The families with significantly more threatened species than average include: Astylosternidae (Cameroonian stream frogs); Hynobiidae (Asian salamanders); Rhacophoridae (Asian tree frogs); Plethodontidae (lungless salamanders); Bufonidae (true toads); and the Leptodactylidae (Neotropical typical frogs). The Astylosternidae are confined to West and Central Africa, with the highest diversity being centred on Cameroon, where they tend to have small ranges at mid-elevations. The midelevation habitats in this region are being heavily impacted through expanding agriculture and deforestation.
The percentage of threatened or extinct amphibian species: a) in each amphibian order; and b) in each amphibian family. Each circle corresponds to an order or family, positioned according to the number of species in the order and the percentage of those species that are threatened (Vulnerable, Endangered or Critically Endangered) or extinct (Extinct or Extinct in the Wild). The horizontal dashed line indicates to the percentage of threatened or extinct species among amphibians as a whole (32%). Orders or families with higher levels of relative threat are depicted above this line, orders or families with lower levels are represented below. The coloured bands indicate the level to which the percentage of threatened or extinct species in each order or family is significantly different from the average. Orders or families with threat levels that are very significantly different from the average (p <0. 01) are listed individually on the right section of the figure. Values between parentheses indicate number of threatened or extinct species/total number of species (e. g. , 27 out of 44 species of the family Hynobiidae are threatened or extinct). For the summary data, see Appendices 3g and 3h.
The announcement in 2003 of the discovery of a new family of frogs, the Nasikabatrachidae, from the Western Ghats of India took the scientific world by surprise. The only species, Nasikabatrachus sahyadrensis (Endangered), is known from only two localities, and spends most of its time deep underground.
Photo: © S.D. Biju
The Hynobiidae are very sensitive to habitat loss, which is severe in parts of their range, and hence have more threatened species than expected. The high level of threat in the Rhacophoridae is mainly a reflection of the large number of threatened species in the genus Philautus. The members of this large genus tend to have very small ranges, especially in India and Sri Lanka, where they are easily impacted by habitat loss. Many species in the Plethodontidae also tend to have very small ranges. The Mexican and Central American members of this family are particularly threatened because of habitat loss. The Bufonidae has the largest number of species that appear to be rapidly declining due to the impacts of chytrid fungus (see Sections 3.7, 3.8 and 6.5 for further details). Most dramatically, 74 of the 77 species in the genus Atelopus (harlequin toads) are threatened or extinct. Other high-profile toad genera with high percentages of threatened species include the viviparous toads of Africa (Nectophrynoides and Nimbaphrynoides). The Leptodactylidae is the largest amphibian family, more than half of which are considered threatened. The family is dominated by the 700 members of Eleutherodactylus (the largest genus of vertebrates), which typically have very small ranges and so are particularly susceptible to habitat loss. Some members of the family have also suffered from the impacts of the chytrid fungal disease, chytridiomycosis.
The Maud Island Frog Leiopelma pakeka (Vulnerable) is one of four members of the primitive New Zealand frog family, Leiopelmatidae, all of which are threatened. This species is confined to a 16 ha forest remnant on Maud Island, although an introduced population was established on Motuara Island in 1997.
Photo: © Philip Bishop
The Seychelles Palm Frog Sooglossus pipilodryas (Vulnerable) is restricted to Silhouette Island in the Seychelles, where it is closely associated with the palm Phoenicophorium borsigianum (Near Threatened). All four members of the frog family Sooglossidae, endemic to the Seychelles, are threatened.
Photo: © Justin Gerlach
The results in Figure 2.5b do not show a number of very small but phylogenetically significant families where all the species are listed as threatened or extinct. These include: Rheobatrachidae (gastric-brooding frogs; both species listed as Extinct); the recently described Nasikabatrachidae from India comprising a single evolutionally unique, threatened species (Biju and Bossuyt 2003); Rhinodermatidae (Darwin's frogs; one species possibly extinct, the other in decline); Leiopelmatidae (New Zealand frogs; all four species threatened, one in serious decline); and Sooglossidae (Seychelles frogs; all four species threatened). The giant salamanders (Cryptobranchidae) are also worthy of mention, with one of the three species being Critically Endangered, and the other two being Near Threatened.
The families with significantly fewer threatened species than average include: Pipidae (tongueless frogs) a group that appears to be generally resistant to disturbance and disease; Ichthyophiidae (Asian caecilians; but many species listed as Data Deficient); Caeciliidae (typical caecilians; but many Data Deficient species); Myobatrachidae (Australian water frogs); Mantellidae (Madagascan frogs); Hyperoliidae (African tree frogs and reed frogs); Microhylidae (narrowmouthed toads); and Hylidae (typical tree frogs). Although the species in these families are less threatened than expected, nearly all of them include a number of very seriously threatened species.
The results for the amphibians differ from those for the mammals and birds in that many of the families with largest percentages of threatened species are species rich (notably Leptodactylidae, Bufonidae, Rhacophoridae and Plethodontidae). However, the amphibian results are similar to mammals and birds in that there are several small, highly threatened families that are phylogenetically unique. It is possible that the massive decline and increasing number of extinctions being observed in the amphibians will lead to a disproportionate loss of evolutionary novelty.
The Anegada Ground Iguana Cyclura pinguis (Critically Endangered) was once distributed over the entire Puerto Rico Bank, but today is confined to the island of Anegada, British Virgin Islands. Vulnerability to predation by humans and their dogs and cats may have resulted in the contraction in range. A reintroduction programme is in place for this species.
Photo: © Glenn Gerber
The reptiles are an under-represented vertebrate group on the IUCN Red List as only 6% of the 8,163 described species have been evaluated so far (see Tables 2.1 and 2.2). The evaluations have tended to focus on particular taxonomic groups that are well known (the crocodilians, turtles, iguanas and tuataras) or on species in the more poorly known groups (lizards and snakes) that are considered to be under threat. Of the species evaluated, 61% are listed as threatened.
Two reptile orders have been completely evaluated, namely the Crocodylia (crocodiles, alligators and caimans) and the Rhynchocephalia (tuataras). The Crocodylia have ten (43%) of their 23 described species listed as threatened. The Chinese Alligator Alligator sinensis is considered the most threatened crocodilian in the world, but there is a large population in captivity and an Action Plan has been drafted to reverse the long trend of habitat loss and population decline for this alligator (Ross 2001). The tuataras from New Zealand are the only surviving members (two extant species) of their order (all other members of the order (and family Sphenodontidae) are known only from the fossil record). One species is listed as threatened and the other is considered to be Least Concern.
The Testudines (turtles and tortoises) are relatively well covered on the IUCN Red List, with 205 (67%) of the 305 described species evaluated, 128 (42%) of which are listed as threatened (see Box 2.2).
Other reptile groups such as the Amphisbaenia (worm lizards) have not been evaluated at all, and likewise very few snakes and lizards have been evaluated. Within the lizards, the main focus has been on the Iguanidae and other closely related families. Many snakes and lizards are cryptic, hard to find and poorly known. However, the Global Reptile Assessment (see Appendix 1) started in 2004 will greatly improve our knowledge of this group of vertebrates.
The Pacific Seahorse Hippocampus ingens (Vulnerable) is traded for traditional medicine, curios and aquaria, and is incidentally caught as bycatch by fisheries along the Pacific coast of Central and South America.
Photo: © Sterling Zumbrunn
Nassau Grouper Epinephelus striatus (Endangered) is found from Bermuda and Florida throughout the Bahamas and Caribbean Sea. The species is fished commercially and recreationally, with much of the catch coming from spawning aggregations.
Photo: © John E. Randall
Yellow-crowned Butterflyfish Chaetodon flavocoronatus (Vulnerable) is endemic to the Mariana Islands. This relatively rare species appears irregularly in the aquarium trade. Little is known about its biology.
Photo: © Tim Allen
Just over 6% of the world's fish species have been evaluated for the IUCN Red List (Tables 2.1 and 2.2). Of the species evaluated, 487 are considered to be purely marine, 1,139 are confined to inland water systems (mainly freshwater) and 96 occur in both marine and inland water systems.
Because marine species have long been considered resilient to extinction, they have, until recently been neglected by extinction risk assessments (but see Boxes 3.8, 4.2 and 6.1). The IUCN Red List includes 131 threatened marine fish species. Amongst the species included are the seahorses and pipefishes (Syngnathidae), groupers (Sarranidae), wrasses (Labridae), damselfishes (Pomacentridae), angelfishes (Pomacanthidae) and the chondrichthyan fishes (sharks, skates and rays). While a number of these species are restricted-range coral reef fishes, some are widespread, commercially valuable species subject to fisheries. As there are so few marine fishes on the IUCN Red List it is premature to analyse the information any further. However, Box 2.3 on the chondrichthyan fishes illustrates some of the issues and the extent to which some marine species are threatened.
For freshwater fish species, because many more have been evaluated, it is not surprising that the number listed as threatened (631 purely freshwater species or 670 that occur in both freshwater and marine) is much higher than for the marine fish. However, the species evaluated are a biased sample as they tend to come from discrete geographic areas: the East African Great Lakes; western Europe; Madagascar; Mexico; South Africa; and the United States. As with the marine species it is premature to analyse these data. However, some of the issues and an indication of the degree of threat faced by freshwater species are presented by means of a case study from East Africa (Box 2.4).
Damba Mipentina Paretroplus maculatus (Critically Endangered) endemic to Madagascar, has undergone severe declines due to severe fishing pressure, impact of introduced inavsive species, and habitat destruction.
Photo: © Paul Loiselle
This East African case study indicates that 27% of the freshwater fishes evaluated in that region are listed as threatened. This figure is comparable to that for North America (United States and Canada) where a recent analysis by NatureServe of the status of 801 species of freshwater fish indicated that 20% are threatened (based on the NatureServe Global Heritage Ranks of G1 – Critically Imperilled and G2 – Imperilled; L. Master pers. comm.; see Box 3.7). It is highly probable that increased attention on freshwater fish species by the SSC over the next few years will confirm a global crisis among these species.
Despite the apparently large numbers of evaluated (3,487 species) and threatened (1,992 species) invertebrates on the IUCN Red List, these numbers are proportionally extremely small when one considers that 95% of all known animals are invertebrates (Hammond 1995). Less than 0.3% of invertebrates are known to have been evaluated, but there is significant under-reporting of Least Concern species, and hence any analysis of the numbers threatened would be misleading (see Tables 2.1 and 2.2). Among those invertebrates that have received the most attention there are some groups with apparently large numbers of threatened species, including 429 primarily inland water crustaceans, 559 insects (mainly butterflies, dragonflies and damselflies), and 974 molluscs (predominantly terrestrial and freshwater species).
The need for a stronger focus on the invertebrate groups has long been recognized, and the SSC is developing a strategy to address this problem (see Appendix 1). In the interim, the list of evaluated invertebrates is slowly increasing, with the most significant changes taking place among the molluscs. Less than five per cent of molluscs have been evaluated and these assessments have largely been confined to terrestrial and freshwater species. The majority of the assessments relate to the better-known regions such as North America, Europe, Australia, as well as recognized areas of endemism on islands.
The East African case study (Box 2.4) includes three freshwater invertebrate groups, the crustaceans, molluscs, and Odonata (dragonflies and damselflies). Based on the species evaluated, 7% of Odonata, 23% of molluscs and 38% of the crabs were listed as threatened. A more comprehensive regional survey of the status of invertebrates has been conducted in North America (Canada and United States), the results of which are presented as a case study (Box 2.5).
Photos 2.20, 2.21 and 2.22 (top to bottom)
South Africa is home to some remarkable threatened molluscs, for example: Photo 2.20 the Dlinza Forest Pinwheel Trachycystis clifdeni (Critically Endangered); Photo 2.21 Purcell's Hunter Slug Laevicaulis haroldi (Endangered); and Photo 2.22 T. haygarthi (Endangered). Many of these species have highly restricted distributions and are therefore sensitive to any habitat disturbance.
Photo: © Dai G. Herbert
The 2004 IUCN Red List includes assessments for 11,824 species of plants, 8,321 of which are listed as threatened (Table 2.3). However, only just over 4% of described plant species (see comments under section 2.2 about the debate on the number of species) have been evaluated, and almost 3% of these are threatened (see Table 2.1).
In considering the numbers of threatened plants it is important to take into account the 33,798 species listed as threatened and extinct in the 1997 IUCN Red List of Threatened Plants; almost 13% of the world's flora at that time (Walter and Gillett 1998). The 1997 Red List was compiled from a database containing information on 139,719 plant taxa (including subspecies, varieties and synonyms). Determining exactly how many species were evaluated for that Red List is difficult, but it is known that 14,861 of these species were not synonyms, were threatened in at least one country, but were not considered to be globally threatened (H. Gillett pers. comm.). Hence the number evaluated for the 1997 Red List probably exceeds 48,659 species. Although an incomplete sample of the global flora, and despite geographic biases (91% of the species listed are single-country endemics, with the largest numbers in Australia, South Africa and the United States), the 1997 Plants Red List stands as the single largest compilation of information on the conservation status of any taxonomic group.
The assessments for the 1997 Plants Red List were done using the pre-1994 qualitative Red List Categories. That system is not strictly comparable to either the 1994 or 2001 versions of the IUCN Red List Categories and Criteria (IUCN 1994a, 2001). Hence the 1997 results are not incorporated into this analysis, but they are used for illustrative purposes.
Since the amalgamation of the plant and animal Red Lists in the 2000 IUCN Red List of Threatened Species™ the number of plant assessments has steadily increased (Table 2.1 and Appendix 3a). Of the 11,824 plants evaluated, 70% (8,321 species) are listed as threatened (Tables 2.1 and 2.3). This partially reflects a bias amongst the botanical community to focus primarily on the threatened species, but there is also a tendency to under-report Least Concern assessments. The focus on threatened species is clearly illustrated by the assessments of bryophytes (mosses, liverworts and hornworts) in Table 2.3, where the subset of 93 species was specifically chosen in order to “provide the public with general information as to which bryophytes are threatened with extinction” (Tan et al. 2000). The same is partly true of the assessments for ferns and fern allies (includes club mosses, spike mosses, quillworts and true ferns), but in this case the 210 species evaluated (although only 1% of the species) represent a widely distributed geographic sample and so might be more representative of the threats faced by this plant group. Certainly the figures of 15% Critically Endangered and 18% Endangered (see Table 2.3) may well be indicative of the degree of threat faced by this plant group.
Table 2.3 Summary of Red List Category classifications by class of plants
A strong bias in the plant assessments in the 2000 IUCN Red List was towards threatened tree species because of the inclusion of the 7,388 species (includes species in all categories from Data Deficient to Extinct) listed in The World List of Threatened Trees (Oldfield et al. 1998). That bias has been slightly reduced through the inclusion of nontree assessments. However, the trees are still dominant with 7,996 species (68%) included on the 2004 IUCN Red List, 5,637 of which are listed as threatened. Many of the recent plant assessments have, however, introduced a geographic bias as they are single country or sub-country endemics (e.g., Cameroon, China, Ecuador, Madagascar, Mauritius, Namibia, Saint Helena, South Africa, Yemen (Soqotra), and the United States (Hawaii)).
As with the invertebrates, the seemingly very large figure of 8,321 threatened plant species is proportionally very small relative to the total number of plant species worldwide (see Table 2.1). The proportion threatened may well be even smaller if the estimated higher numbers of seed plants is shown to be correct (1.84% versus 2.89%). It is therefore premature at this stage to attempt any detailed analysis of the plants as the low numbers evaluated and the strong biases towards trees and certain geographic areas misrepresents the overall picture for plants. For further details on the numbers of plants in each category, see Tables 2.1 and 2.3, and the detailed order and family results in the Summary Statistics tables on the Red List web site (www.iucnredlist.org).
Despite the low numbers evaluated and the biases, some trends are evident for plants. Two classes of plants have been fully evaluated, namely the cycads and the conifers (with the exception of two species of conifer). Whether these gymnosperm groups are representative of what is happening to plants generally is debatable. However, both are relatively ancient lineages and clearly illustrate very different threats and trends (see Figures 2.6a and b). Although there are almost equal numbers of threatened conifers and cycads (153 and 151 respectively), the proportion of cycads that are threatened is considerably higher. For the conifers, 25% of the species are listed as threatened (17 Critically Endangered, 43 Endangered and 93 Vulnerable). The 1997 IUCN Red List of Threatened Plants (Walter and Gillett 1998) lists 30% of conifers in the old Endangered (E) and Vulnerable (V) categories. For cycads, 52% of the species are listed as threatened (47 Critically Endangered, 39 Endangered and 65 Vulnerable). In addition, a further 23% of cycad species are considered Near Threatened. The cycads are listed as threatened because they have small and declining populations and/or small ranges. At present the cycads are the most threatened plant group known, and are one of the most threatened taxonomic groups on the Red List. As with many of the threatened vertebrates, the conifers and cycads are unique phylogenetic lineages indicating that perhaps non-random extinction (as demonstrated for the mammals, birds and amphibians in section 18.104.22.168) is also happening in the plant kingdom. The cycads in particular are a unique lineage of plants that survived the last extinction spasm and which are now facing imminent extinction in the wild as a direct result of human activities.
Ossiculum aurantiacum (Critically Endangered) is a highly attractive epiphytic orchid endemic to the Cameroon. It has not been seen again in the wild since it was first collected in 1980, despite intensive searching in the area.
Photo: © Henk Beentje
Maui Hesperomannia arbuscula (Critically Endangered) is a small shrubby tree known only from the Hawaiian Islands of Maui and Oahu. Main threats are habitat degradation by pigs, competition with alien plant species, predation by rats, and from trampling or collecting by humans.
Photo: © Vickie L. Caraway
The Pokemeboy Acacia anegadensis (Critically Endangered) is endemic to Anegada, British Virgin Islands. Few mature trees now survive because of past exploitation for resin from these trees.
Photo: © Colin Clubbe
The Monkey Puzzle Araucaria araucana (Vulnerable) ranges from the Coastal Cordillera of Chile to the Andes in Argentina. The timber is widely used and many trees are illegally felled.
Photo: © Cristian Echeverria
The Drakensberg Cycad Encephalartos ghellinckii (Vulnerable) although well-protected in the northern parts of its range in KwaZulu-Natal, South Africa, has suffered declines in the southern parts of its range due to human exploitation for the horticultural market.
Photo: © Craig Hilton-Taylor
Percentages of extant species in each Red List Category for conifers and cycads. The pie charts exclude the categories Extinct, Extinct in the Wild and Not Evaluated.
The proportions of threatened monocotyledons (Liliopsida) and dicotyledons (Magnoliopsida) are very similar (Table 2.3). However, it is clear that the 10,614 flowering plants that have been evaluated so far are very much a biased sample towards those that are more threatened. Interestingly though, the families that emerge as having the most threatened species are also some of the most speciose and cosmopolitan e.g., Araceae (118); Compositae (324); Dipterocarpaceae (369); Euphorbiaceae (359); Gramineae (64); Leguminosae (589); Orchidaceae (146); Palmae (238 species); and Rubiaceae (369). These families include many plants of major economic importance as food crops, sources of timber and building materials, medicines, and as ornamentals. The loss of these plant species will have major socio-economic implications in the future.
There is much debate about the size of the world's threatened flora. Pitman and Jørgensen (2002) consider the commonly cited figure of 13% (derived from Walter and Gillett 1998) too low and suggest that the true figure may be closer to 50% of all known plants. Bramwell (2003) argues that a figure of 50% exaggerates the scale of potential plant extinction, and that the true figure is probably about 21%. A case study comparing comprehensive assessments of plants endemic to two areas, namely mainland Ecuador - a biodiversity hotspot (Myers et al. 2000) and the islands of Soqotra - a recognized Center of Plant Diversity (Miller and Guarino 1994), is presented (Box 2.6). In both instances the percentage of the total flora threatened is 18-19%, figures very close to the estimate proposed by Bramwell (2003).
The SSC has an ambitious programme to increase the coverage of plants on the IUCN Red List over the next few years, as it strives to meet the 2010 CBD target of obtaining a preliminary conservation assessment of the world's described plant species (see Appendix 1). As the assessments increase it will be interesting to determine whether or not the patterns observed in mainland Ecuador and in Soqotra are repeated elsewhere in the world.
The fungi, lichens and the seaweeds (red algae) have traditionally been considered members of the plant kingdom, but are now treated under separate kingdoms. These taxonomic groups have not been the focus for any Red List activity; however, there are probably many species in these groups that are facing extinction. In 2003, three species from these groups were evaluated and entered into the IUCN Red List for the first time, thereby expanding the Red List coverage to four kingdoms. These were two threatened lichens and an Extinct red alga from Australia (Table 2.4; see also Box 3.5). While these species pose particular challenges on how to apply the Red List Criteria, it is hoped that this small start will lead to a greater focus on these neglected but important organisms.
Table 2.4 Summary of Red List Category classifications by class of other organisms
15,589 species are threatened with extinction. This includes 12% of all bird species, 23% of mammals evaluated, 32% of all amphibians, and 31% of all gymnosperms.
Although a significant proportion of the world's biodiversity faces extinction, it is not possible to quantify how many species are at risk because we have not yet named all the species, the baseline checklists are constantly changing, and we have yet to assess the bulk of the world's species.
The risk of extinction is best known for the vertebrates, in particular the amphibians, birds and mammals.
The numbers of threatened species are increasing across virtually all the major taxonomic groups.
Amphibians have been completely assessed for the first time, and have a higher percentage of threatened species, particularly Critically Endangered ones, than either the birds or the mammals.
The extinction risk for amphibians may be under-estimated as 23% of them are listed as Data Deficient.
Threatened species are not randomly distributed across orders and families. A number of families have significantly more threatened species than would be expected on average, while others have far less. The nonrandom distribution means that entire evolutionary clades are liable to go extinct very quickly.
While reptiles are generally under-represented on the IUCN Red List, the turtles and tortoises are relatively well represented with 42% threatened with extinction.
The increasing number of sharks, rays and chimaeras on the Red List demonstrates that these marine species might be as threatened as some terrestrial groups, especially because of their slow life histories, low population growth rates and their inability to withstand the increasing fishing pressures around the world.
A freshwater case study from East Africa shows the value of multi-taxa regional assessments for conservation planning and provides an insight about the degree of threat faced by freshwater species.
Invertebrates are poorly represented on the Red List, with assessments confined to the better-known groups such as butterflies, inland water crustaceans, dragonflies and molluscs. A case study from the United States indicates that some invertebrate groups are likely to be highly threatened globally.
Plants are also poorly represented on the Red List, despite being the taxonomic group with the largest numbers evaluated.
Two classes of plants have been completely assessed, the conifers and the cycads. The cycads are one of the most threatened groups of species on the Red List with 52% listed as threatened.
A case-study comparing evaluations of all endemic plants from mainland Ecuador and the island group of Soqotra, supports the argument that approximately 21% of the world's flora may be threatened.
The IUCN Red List now includes three representatives from two other kingdoms – the Protista and the Fungi.
The Boreal Felt Lichen Erioderma pedicellatum (Critically Endangered) is one of only two species of fungi on the IUCN Red List. This lichen has completely disappeared from New Brunswick (Canada), Norway and Sweden. The only remaining populations are in Nova Scotia and Newfoundland, Canada. Major threats are habitat destruction through logging and air pollution.
Photo: © Christoph Scheidegger.
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