Photo 4.1
The striking Rufous-collared Kingfisher Actenoides concretus (Near Threatened) is confined to the Sundaic lowlands. Forest destruction in the Sundaic lowlands of Indonesia has been so extensive that all primary formations are expected to disappear by 2010, and the situation is little different in Thailand and Malaysia.
Photo: © Jacob Wijkema.
The world's biodiversity is being destroyed rapidly (Balmford et al. 2003; Jenkins et al. 2003). It is important to quantify this by measuring trends in the status of biodiversity in order to gain a better understanding of the impact that humans are having, and to determine how successful we are at addressing biodiversity loss. In particular we need indicators for measuring progress towards achieving the target set by the nations of the world for significantly reducing the rate of loss of biological diversity by 2010. We do not yet have an adequate way of monitoring progress towards achieving this target. However, the Convention on Biological Diversity (CBD) has recommended developing a number of indicators, including one based on changes in status of threatened species.
Here we present “Red List Indices” (RLIs) which show how the overall threat status (projected extinction risk) of particular sets of species changes over time. These are based on the number of species in each Red List Category and the number changing between categories as a consequence of genuine improvement or deterioration in status (see Appendix 2d for further details). The Red List Programme developed the RLI because changes in the total number of species on the IUCN Red List (or in different categories) over time cannot simply be used to examine trends in the threat status of sets of species, for several reasons. For example, many category changes result from improved knowledge or taxonomic revisions, but such revisions are not indicative of changes in overall status. Furthermore, in many taxonomic groups the subset of species that have been assessed for the IUCN Red List may be biased towards rare, well known, or high profile species or those from particular regions or families. Using data on the world's birds and amphibians, these problems have been overcome to produce RLIs that are robust, temporally sensitive, representative and comprehensive. They provide unique baseline data against which progress towards meeting the CBD 2010 target can be judged, and they allow finer-scale resolution of trends in particular biogeographic realms, ecosystems and habitats.
The Red List Index (RLI) for birds shows that there has been a steady and continuing deterioration in the threat status (projected extinction risk) of the world's birds between 1988 and 2004, with an overall change in the index value of - 6.90% over this period (Figure 4.1). No change would indicate that the average status of all bird species was the same as in 1988. To put this into context, if 10% of species in categories Near Threatened (NT) to Critically Endangered (CR) had deteriorated in status sufficiently to be uplisted one category (i.e., to a category of higher threat) between 1988 and 2004, the index would have changed by -7.8% (Figure 4.1). It is worth noting that species often have to undergo considerable changes in population size, population trend or range size in order to cross thresholds between categories and hence contribute to trends in the RLI. However, almost half of all threatened bird species are estimated to have declined in status during 2000–2004 regardless of whether or not they were uplisted to higher categories of threat (see Box 4.1).
Figure 4.1
The Red List Index (RLI) for all bird species for 1988–2004 (250 genuine status changes out of 2,469 species in categories Extinct in the Wild (EW) to Near Threatened (NT) in at least one assessment), with hypothetical indices showing trends if no species had changed category, and if 10% of species in the categories from NT to Critically Endangered (CR) had been uplisted to a higher category of threat or downlisted to a lower category of threat over the period. Error bars for 2004 RLI value are based on estimated number of genuine status changes for 2000–2004 not yet detected owing to information time-lags (see Appendix 2d for further details of methods).
The Red List Index measures movement between categories of the IUCN Red List. However, these categories are relatively broad; species often have to undergo considerable changes in population size, population trend or range size in order to cross the thresholds between categories. To determine qualitative trends between 2000 and 2004 in the status of all threatened bird species, not just those moving between Red List Categories, a worldwide network of over 100 experts was consulted. They were asked to judge from their detailed knowledge whether the status of each species had improved, stayed the same, or deteriorated during the period. Assessments were obtained for 72% of threatened birds (859 species). Of these, only 11% were judged to have improved in status, 43% had remained the same and 45% had deteriorated in status since 2000 (see Figure below). Similar proportions were found for the subset of Critically Endangered species: 14% were judged to have improved in status, 40% had stayed the same, and 46% had deteriorated in status. Of the species for which the experts scored ‘unknown’ status changes or for which no assessment could be obtained, many were also likely to be declining. In combination with declining trends shown by the Red List Index, this snapshot survey indicated that threatened birds are in serious trouble, and that the problem is getting worse.
Figure Box 4.1
Changes in the status of the world's threatened birds 2000–2004 according to ‘expert’ assessment.
Taken from BirdLife International (2004b).
Disaggregating the RLI shows that the threat status of birds has deteriorated worldwide at a more-or-less similar rate and proportional extent in the Nearctic, Neotropical, Palearctic, Afrotropical and Australasian/Oceanic realms. The Indomalayan realm shows a steeper rate of deterioration during the 1990s (see Figure 4.2). This was a result of the intensifying destruction of forests in the Sundaic lowlands of Indonesia, which escalated particularly in the late 1990s and led to predictions of almost total loss of lowland forest in Sumatra by 2005 and in Kalimantan by 2010 (Holmes 2000; Collar et al. 2001). As a consequence of these increasing rates of habitat loss, many species were uplisted to higher categories of threat under criterion A (rapid population declines). However, it is notable that there has been a substantial deterioration in the threat status of birds of shrubland/grassland habitats as well as forest, and in the two other major ecosystems (freshwater and marine), indicating that birds in a broad spectrum of environments are deteriorating in status (Figure 4.3).
Photo 4.2
Rhinoceros Hornbill Buceros rhinoceros (Near Threatened) from the Sundaic lowlands of Indonesia, Malaysia and Thailand. Threatened by forest destruction and in parts of its range by hunting for food and hat feathers.
Photo: © Dr. Chan Ah Lak.
Photo 4.3
The wide ranging Black-browed Albatross Thalassarche melanophrys (Endangered) was uplisted from Vulnerable in 2003. All 21 species of albatross are now listed as globally under threat (compared to just three in 1996 and 16 in 2000). All are undergoing long-term declines, with significant numbers drowning after being caught accidentally on baited hooks set by longline fisheries.
Photo: © Tony Palliser / BirdLife International.
Figure 4.2
Red List Indices (RLIs) for birds in different biogeographic realms for 1988–2004. Sample sizes: Afrotropical = 41 genuine status changes out of 394 species in categories Extinct in the Wild (EW) to Near Threatened (NT) in at least one assessment; Indomalayan = 100 out of 585 species; Nearctic = 9 out of 92 species; Neotropical = 49 out of 834 species; Australasian/Oceanic = 53 out of 614 species; Palearctic = 34 out of 238 species.
Figure 4.3
Red List Indices (RLIs) for birds in the marine, freshwater and terrestrial ecosystems, and for birds in forest and shrubland/grassland habitats, for 1988–2004. Sample sizes: Marine = 12 genuine status changes out of 133 species in categories Extinct in the Wild (EW) to Near Threatened (NT) in at least one assessment; Freshwater = 31 out of 226 species; Terrestrial = 206 out of 2329 species; forest = 169 out of 1,513 species; shrubland/grassland = 45 out of 481 species.
Breaking down the RLI for birds by particular families or species-groups shows that the threat status of albatrosses and petrels has deteriorated particularly severely in recent years (Figure 4.4). This is closely linked to the expansion of commercial longline fisheries (both legal and illegal), which cause incidental mortality of albatrosses and other seabirds when they are caught on baited hooks and drown (Tuck et al. 2001, 2003; BirdLife International 2004b).
Figure 4.4
Red List Indices (RLIs) for five bird families and species-groups for 1988–2004. Sample sizes: Waterbirds = 36 genuine status changes out of 238 species in categories Extinct in the Wild (EW) to Near Threatened (NT) in at least one assessment; Raptors = 10 out of 93; Gamebirds = 15 out of 123; Parrots = 19 out of 148; Albatrosses and petrels = 6 out of 28).
The RLI for amphibians, based on assessments in 2004, and retrospective classifications for 1980 (see Appendix 2d for methods), shows that the threat status of the world's amphibians has deteriorated substantially (Figure 4.5). The index value changed by -13.7% over this period. The net decline is equivalent to c. 30% of species in each 1980 category from Near Threatened (NT) to Critically Endangered (CR) being uplisted by one category (i.e., to a category of higher threat; Figure 4.5). Furthermore, the rate of deterioration is likely to have been underestimated: a conservative approach was adopted in identifying genuine deteriorations between 1980 and 2004. In addition, 23% of amphibians are listed as Data Deficient (and hence are excluded from the RLI), and with better information many of these may well prove to be threatened and to have undergone serious declines through this period.
It is also worth noting that, out of the 4,048 amphibian species (70.9%) for which trends have been recorded, 61.0% (2,468 species) are estimated to be declining, 38.3% (1,552 species) are stable, and just 0.69% (28 species) are increasing.
Photo 4.4
Darwin's Frog Rhinoderma darwini (Vulnerable) from central Chile and nearby Argentina is one of only two members of the family Rhinodermatidae. The females deposit eggs in the leaf litter. When the larvae inside the eggs begin to move, the adult males ingest the eggs and incubate them in their vocal sacs. The larvae develop inside the male and emerge after metamorphosis, as shown in this photo. This species appears to be in decline, even in well protected habitats, for unclear reasons. The only other member of the family, Rhinoderma rufum from Chile, disappeared around 1978, and it is Possibly Extinct.
Photo: © Michael and Patricia Fogden.
Figure 4.5
A preliminary Red List Index (RLI) for all amphibian species for 1980–2004 (retrospective assessment; 496 genuine status changes out of 2,225 species in categories Extinct in the Wild (EW) to Near Threatened (NT) in at least one assessment), with hypothetical indices showing trends if no species had changed category, and if 10% or 30% of species in the categories from NT to Critically Endangered (CR) had been uplisted to a higher category of threat or downlisted to a lower category of threat over the period.
The RLI for amphibians in different realms shows that species in the Australasian/Oceanic realm have shown the steepest deterioration in status, followed by those in the Palearctic and Neotropical realms (Figure 4.6). However, the steep rate of deterioration in the Australasian/Oceanic realm is probably biased by the fact that a large proportion of species are listed as Data Deficient in this region (31.6% compared to a mean of 21.6% in all other realms). Many of these are in the family Microhylidae (narrow-mouthed toads - 61.6% compared to 3.9% in all other realms), which is one of the groups least affected by the fungal disease chytridiomycosis (believed to be one of the major threats to amphibians: see section 6). This family is especially diverse in the remote, poorly surveyed regions of New Guinea, where it is the dominant component in the frog fauna. Data Deficient species are excluded when calculating the index value, giving any genuine status changes a greater proportional significance. Further information is likely to show that the majority of these Australasian/Oceanic Data Deficient species have not undergone substantial status changes over the period, giving a RLI for this realm that shows a smaller rate of decline. The severity of the declines in the Palearctic realm is largely driven by the increasing levels of exploitation of amphibians in China over the period, while the steep decline in the RLI for amphibians in the Neotropical realm largely reflects the severe impacts that chytridiomycosis appears to have had on these species.
Photo 4.5
The spectacular Corroboree Frog Pseudophryne corroboree (Critically Endangered) has declined dramatically in distribution and abundance, and is now restricted to a few fragmented populations in subalpine and montane areas of New South Wales, Australia. Fewer than 250 mature individuals are thought to survive.
Photo: © Harold Cogger.
Photo 4.6
The Green-eyed Frog Rana vibicaria (Critically Endangered) was once abundant in Costa Rica and western Panama. Its populations crashed in the late 1980s, and there were no records in Costa Rica after 1990, until 2002 when a small population was rediscovered. There have been no recent records from Panama.
Photo: © Michael and Patricia Fogden.
Photo 4.7
This species of harlequin toad, Atelopus varius (Critically Endangered), was once abundant in Costa Rica and western Panama. Over 100 separate populations were once known from Costa Rica. Declines began at Monteverde in 1988, and by 1996 it was believed to be extinct in Costa Rica. Serious population crashes have also taken place in Panama, though it was recorded as recently at 2002. A small population was rediscovered in Costa Rica in 2003.
Photo: © Michael and Patricia Fogden.
Figure 4.6
Preliminary Red List Indices (RLIs) for amphibians in different biogeographic realms for 1980–2004 (retrospective assessment). Sample sizes: Afrotropical = 29 genuine status changes out of 287 species in categories Extinct in the Wild (EW) to Near Threatened (NT) in at least one assessment; Indomalayan = 60 out of 399 species; Nearctic = 29 out of 118 species; Neotropical = 332 out of 1,260 species; Australasian/Oceanic = 38 out of 88 species; Palearctic = 36 out of 148 species.
The threat status of amphibians in the freshwater and terrestrial ecosystems has deteriorated at broadly similar rates (Figure 4.7). This is to be expected, because 64.0% of species are common to both ecosystems. Nevertheless, declines have been more severe for freshwater amphibians. This is likely to be because chytridiomycosis appears to have a greater impact on freshwater species (Berger et al. 1998; Lips et al. 2003), and because such species are often sensitive to changes in water quality such as those brought about by logging (Inger 1966; Amiet 1989). Although terrestrial species often have tiny ranges, this does not seem to be sufficient to compensate for the greater susceptibility of freshwater-dependent species.
Figure 4.7
Preliminary Red List Indices (RLIs) for amphibians in freshwater and terrestrial ecosystems for 1980–2004 (retrospective assessment). Sample sizes: freshwater = 381 genuine status changes out of 1,369 species in categories Extinct in the Wild (EW) to Near Threatened (NT) in at least one assessment; terrestrial = 473 out of 2,151 species.
Figure 4.8
Preliminary Red List Indices (RLIs) for selected amphibian families for 1980–2004 (retrospective assessment). Sample sizes: Bufonidae: 106 genuine status changes out of 233 species in categories Extinct in the Wild (EW) to Near Threatened (NT) in at least one assessment; Leptodactylidae: 121 out of 584 species; Hylidae: 68 out of 241 species; Ranidae: 56 out of 222 species; Microhylidae: 10 out of 89 species; Plethodontidae: 34 out of 204 species.
Some families of amphibians have undergone more serious declines than others (Figure 4.8). Of the larger amphibian families, toads (Bufonidae) have shown the steepest rate of deterioration in threat status, and this is probably a reflection of the high level of susceptibility of the genus Atelopus to chytridiomycosis (Lötters et al. 2003).
The Red List Indices for birds (1988–2004) and amphibians (1980–2004) show remarkably similar slopes (changing by -0.422% per year for birds and -0.571% per year for amphibians; Figure 4.9). For birds there were 250 genuine category changes over 16 years (1988–2004). This represents 15.8% of species in categories Near Threatened (NT) to Critically Endangered (CR) in 1988 moving to higher or lower categories by an average of 1.21 categories, which equates to c. 10% of species in each category from NT to CR deteriorating by one category (Figure 4.1). For amphibians, 496 species underwent genuine category changes over 24 years (1980–2004). This represents 24% of species in categories NT to CR in 1980 changing on average 1.46 categories (nearly all deteriorating), equating to c. 30% of species in categories NT to CR deteriorating by one category (Figure 4.5). In other words, a higher proportion of amphibians deteriorated in threat status, and they did so by a greater degree, but when this is considered over the longer time-frame compared to birds (24 years vs. 16 years), the rate of decline of RLI is similar. This is presumably because many bird and amphibian species that underwent status changes during these time periods will have been impacted in a similar way by the same habitat loss. However, amphibians have also been severely impacted by chytridiomycosis. It is presumably a coincidence that the proportion of amphibians that have changed status as a result of this threat more-or-less balances the proportion of birds impacted by, for example, exploitation or invasive species (a particularly significant threat on oceanic islands, where there are few amphibians).
To examine trends in the status of the most threatened species, we can examine RLIs with each category weighted by its relative extinction risk (see Appendix 2d for details). Movements of species in and out of the highest threat categories largely drive trends in such indices. The preliminary RLI weighted by extinction risk for amphibians shows a much steeper decline than the equivalent bird index (Figure 4.10). This is because a much higher proportion of amphibians than birds moved into the Critically Endangered (CR) and Critically Endangered (Possibly Extinct) (CR(PE)) categories over the period (see Appendix 2c for a definition of Possibly Extinct). The allocation to CR(PE) was less strictly applied to amphibians compared to birds (see Appendix 2c). However, when the index value was recalculated setting all CR(PE) species to CR, the index still shows a rapid decline, indicating a genuine deterioration in the status of amphibians in the highest categories of threat.
Figure 4.9
The Red List Index (RLI) for all bird species for 1988–2004 and a preliminary RLI for all amphibians for 1980–2004 (retrospective assessment). Sample sizes: birds: 250 genuine status changes out of 2,469 species in categories Extinct in the Wild (EW) to Near Threatened (NT) in at least one assessment; amphibians: 496 out of 2,225 species. Error bars for 2004 RLI value for birds based on estimated number of genuine status changes for 2000–2004 not yet detected owing to information time-lags (see Appendix 2d for further details of methods).
The RLI weighted by extinction risk for birds shows that the rate of deterioration appeared to almost level out during 2000–2004 (although the error bars indicate that in the next few years the belated discovery of genuine status changes for this period could reduce this apparent levelling out; Figure 4.10). This is because for the species closest to extinction, the number that deteriorated in status was almost balanced by the number improving in status owing to conservation action. However, it should be emphasised that one Critically Endangered species went Extinct in the Wild during the period (Hawaiian Crow Corvus hawaiiensis), and another is highly likely to have done so (Spix's Macaw Cyanopsitta spixii).
Figure 4.10
The Red List Indices (RLIs) weighted by extinction risk for all bird species for 1988–2004 and for all amphibian species for 1980–2004 (retrospective assessment). Sample sizes: birds: 250 genuine status changes out of 2,469 species in categories Extinct in the Wild (EW) to Near Threatened (NT) in at least one assessment; amphibians: 496 out of 2,225 species). Error bars for 2004 RLI value for birds based on estimated number of genuine status changes for 2000–2004 not yet detected owing to information time-lags (see Appendix 2d for further details).
Appendix 3a gives the total number of threatened species for each major taxonomic group on the IUCN Red List from 1996 to 2004. In many groups, the numbers of threatened species have increased in recent years. However, as discussed earlier, the total numbers cannot be used to interpret trends in the status of species, because many category changes result from improved knowledge or taxonomic revisions. Only for birds and amphibians have these different reasons for change been analysed. Among the other groups, future analysis is likely to identify significant numbers of species that underwent genuine deteriorations in status during 2000–2004 among primates (owing to increasing levels of habitat loss and hunting) and tortoises and freshwater turtles (owing to unsustainable levels of exploitation in Southeast Asia).
Currently, Red List data on population trends are generally inadequate for analysis for most groups other than birds and amphibians. There are some notable exceptions: for example, population trends are available for 260 species of cycads (Cycadopsida, 288 species in total). Of these, 79.6% (207 species) are declining, 20.4% (53 species) are stable and none are considered to be increasing. Trend information can also be inferred for many marine fishes from fisheries data, despite the lack of Red List assessments, indicating major declines (see Box 4.2).
Photo 4.8
Cycas tansachana (Critically Endangered) a treelike cycad known only from limestone outcrops near Saraburi, Thailand. The plant is restricted in occurrence and under severe pressure from plant collectors and limestone mining operations in the area.
Photo: © John S. Donaldson.
Marine fishes are among the poorest represented groups on the IUCN Red List, as only 487 of a potential 15,000 species have been assessed. Although Red List data are not complete enough to infer trends in the status of threatened marine fishes over time, data from marine fish groups that are well assessed (chondrichthyan fishes (sharks, rays and chimaeras), syngnathids (seahorses and relatives) and groupers and wrasses) do indicate clearly that exploitation is an important and significant threat to marine species. Despite the lack of Red List assessments, there is plenty of evidence from fisheries data to suggest that the conservation status of exploited marine species is deteriorating.
Fisheries data collected by the Food and Agriculture Organization (FAO) of the United Nations illustrate the rapidly worsening status of exploited marine fishes. FAO has analysed landings records for 200 major fishery resources that account for 77% of world marine fish production. The fisheries have been classified according to four stages of a generalized fishery development model. In the first ‘Undeveloped’ stage, catches are low and steady, in the second ‘Developing’ stage catches are rising rapidly, in the third ‘Mature’ phase, catches reach a peak and start to fall, and in the final ‘Senescent’ stage, catches are dropping rapidly and the fishery is overexploited. Their analysis shows a striking shift from undeveloped to senescent fisheries over the last fifty years. Specifically, 60% of the world's major fish resources are mature or senescent and therefore in need of urgent management and conservation attention (FAO 1997a).
These severe fishery declines are of great importance when considering the extinction risk of an exploited species, even though the concept of collapsed fisheries being threatened with extinction is only recently becoming more acceptable. A lack of recovery from low numbers, and low potential recovery rates from low numbers are both logical, defensible metrics of extinction risk. It is often assumed that fishing mortality is the primary factor inhibiting population recovery but this is not the case, as illustrated by the failure by Atlantic Cod Gadus morhua, as well as many other commercially exploited species, to recover following its collapse (Hutchings 2001).
Photo 4.9
The Humphead Wrasse Cheilinus undulatus (Endangered) is widely distributed but is nowhere common. Wherever it is fished, even if only moderately, density quickly declines and it appears to be extirpated from several edge of range locations. It is particularly heavily exploited at the centre of its range in southeastern Asia for the live reef fish trade. Fishery-dependent and trade-related data suggest declines over the last 10–15 years in exploited areas.
Photo: © John E. Randall.
Photo 4.10
Catches of the Whale Shark Rhincodon typus (Vulnerable) have declined with populations apparently depleted by harpoon fisheries in several countries targeting localized concentrations of this huge, slow-moving and behaviourally-vulnerable species, and there is incidental capture in other fisheries.
Photo: © Wolcott Henry.
Based on information provided by Elodie Hudson
The IUCN Red List is a valuable source of data for examining trends in the state of biodiversity.
Red List Indices provide a robust way of illustrating the net changes to the threat status of particular groups over time.
Red List Indices show that birds and amphibians are slipping towards extinction at an increasing rate.
Underlying data draw attention especially to threats from forest loss and long-line fisheries (birds) and disease, habitat loss and exploitation (amphibians).
The limited information on overall trends for other taxonomic groups suggests that declines are occurring in these groups too.
The IUCN Red List Programme is improving the taxonomic coverage of the Red List Indices.