Table Of ContentJournal ofthe Bombay Natural HistorySociety, 106(3), Sept-Dec 2009 230-244
THE EXTINCTION CRISIS: FACT OR FICTION?
Simon N. Stuart1
'International UnionforConservationofNature(IUCN) Species SurvivalCommission, 1196Gland, Switzerland;
UnitedNationsEnvironmentalProgrammeWorldConservationMonitoringCentre,A1AinWildlifeParkandResort,A1Ain,
UnitedArabEmirates; andDepartmentofBiology andBiochemistry,UniversityofBath,BathBA27AY, UK.
Email: [email protected]
Therapiddisappearanceofspecies isoften referredto in a substantial and largely irreversible loss in the diversity
asonetheworld’sgreatestenvironmentalconcerns.TheIUCN oflife onearth.
Red List ofThreatened Species, which now includes more The structure and function of ecosystems have
than44,000animalandplantspecies,showsthatnearlyone- undergone unprecedented changes through the severe
quarterofthe planet’s 5,488 mammals and nearly one-third impacts of human activities. Land conversion, habitat
of the 6,255 amphibians are globally threatened or extinct. change, pollution, overexploitation, invasive species and
Similarly, worrying patterns ofthreatanddecline have been climate change are the direct drivers of threats that are
found in other groups, such as birds, reef-building corals, compromisingthecontinuedprovisionofessentialecosystem
andgymnosperms. services.
TheIUCNRedLististheworld’smostcomprehensive According to the Millennium Ecosystem Assessment
informationsourceontheglobalconservationstatusofplant (2005),since 1945,morelandhasbeenconvertedtocropland
and animal species. Completed and ongoing assessments than in the 18th and 19th centuries combined. In the last
revealthelevelofthreattospecies(highlightingthosefacing severaldecades,20%oftheworld’scoralreefswerelostand
a high risk ofglobal extinction) whilst also identifying the a further 20% degraded; there has been a similar impact on
—
nature and distribution of major threats. Mapping the mangrove areas a 35% loss in the last several decades.
distribution of threatened species has identified that the The amount of water in reservoirs has quadrupled, and
proportion of threatened species differs markedly between withdrawals fromrivers and lakeshave doubled since 1960.
groups and that the pattern ofthreat ofone group does not Transformationshave alsooccurredacrossallofthe world’s
predict the pattern ofthreat for another. The distribution of biomes: between 1950 and 1990, 5-10% ofthe area offive
threatened species also shows very different patterns biomes had been converted. By 1990, more than two thirds
compared with depictions ofoverall diversity. ofthe area oftwo biomes and more than halfofthe area of
Numbers of threatened species are increasing across four others had been converted. (Millennium Ecosystem
virtually all the major taxonomic groups. There are many Assessment2005).
drivers of species extinction, all arising either directly or Increasing human populations have a much greater
indirectly from human activities. Overwhelmingly,themost collectiveimpactontheirsurroundingsparticularlywhentheir
commonthreatishabitatloss,butover-harvesting,incidental activities lead to excessive volumes of nutrients entering
mortality, disease, pollution, and climate change are also ecosystems. The flow ofreactive nitrogen on the continents
majorinfluences on the rate ofspecies decline. has already doubled, and some projections suggest that this
may increase further by approximately two-thirds by 2050.
The Global Context Excessive nitrogen flows have severeenvironmental effects
Biodiversity loss is one of the world’s most pressing (eutrophication of freshwater and coastal ecosystems,
crises, with many species declining to critically low levels contribution to acid rain, and loss of biodiversity), which
and with significant numbers going extinct. Biodiversity is contribute to creation ofground-level ozone, destruction of
essential for mankind because many a number of species, ozone in the stratosphere and global warming, all ofwhich
andtheecosystemstheyform,providethevastarrayofgoods havesubsequentadverseeffectsonhumanhealth(Millennium
and services that sustain our lives. However, despite the EcosystemAssessment2005).
immensevalueofbiodiversity,overthepast50yearshumans By the end of the century, climate change and its
havechangedecosystems morerapidlyandextensivelythan impacts may be the dominant direct drivers ofbiodiversity
in any comparable period of time in human history lossandchangesinecosystemservicesglobally.Thebalance
(MillenniumEcosystemAssessment2005).Thishasresulted ofscientificevidencesuggeststhattherewillbeasignificant
PaperreadattheInternationalConferenceon ‘ConservingNatureinaGlobalizingIndia’ atBengaluru;February 17-19,2009
THE EXTINCTION CRISIS: FACTOR FICTION?
net harmful impact on ecosystem services worldwide, if to population trend, population size and structure, and
global mean surface temperatures increase more than 2 °C geographic range (Mace et al. 2008). Species classified as
above pre-industrial levels. This would require C0 Vulnerable, Endangered and Critically Endangered are
2
stabilisation at less than 450 ppm (Millennium Ecosystem regardedas ‘threatened’.TheIUCNRedListCriteriacanbe
Assessment2005). used to assess the conservation status ofany species, apart
The changes that have been made toecosystems have frommicroorganisms.
contributedtosubstantialnetgainsinhumanwell-being and The IUCN Red List is compiled and produced by the
economicdevelopment.However,oftenthesegainshavebeen IUCN Species Programme based on contributions from a
achieved at growing costs. Due to the degradation ofmany network ofthousands ofscientific experts around the world
ecosystem services, levels of poverty have remained high, intheIUCNSpeciesSurvivalCommission.Assessmentsare
and inequities are growing. It is estimated that 1.1 billion impartial and peer-reviewed, providing objective data to
people are surviving on an income ofless than $1 per day, support national, regional and global conservation priority
70% of whom are in rural areas where they are highly setting. It is updated regularly and is freely available The
dependent on ecosystem services (Millennium Ecosystem Red List is used for many purposes, as summarised in
Assessment2005). Rodrigues etal. (2006) and Vie etal. (2009).
Many people are still unable to access an improved One of the IUCN Red List’s main purposes is to
water supply, and more than 2.6 billion lack access to highlight those species that are facing a high risk ofglobal
improvedsanitation.Waterscarcityaffectsroughly 1-2billion extinction. However, it is not just a register of names and
people worldwide and will continue to worsen, as 5% to associatedthreatcategoriesbutitisalsoarich,expert-driven
possibly 25% of global freshwater use exceeds long-term compendium of information on species’ ecological
accessible supplies. On an average, irrigation withdrawals requirements,geographicdistributions(includingmaps)and
exceed 15-35%ofsupplyratesandarethereforeunsustainable threats.TheRedListisusedtodeterminewhatthechallenges
(MillenniumEcosystemAssessment2005). to nature are, where they are operating and how to combat
Mostdirectdriversofdegradationinecosystemservices them.
are growing in intensity in most ecosystems or at best are Byassessingthethreatstatusofspecies,theIUCNRed
remaining constant (Millennium Ecosystem Assessment Listhastwogoals: (i)toidentifyanddocumentthosespecies
2005). The result is that we live in an increasingly mostinneedofconservationattentioniftheglobalextinction
unsustainable world.Thisis thecontextinwhichweneedto rates are to be reduced, and (ii) to provide a global index of
consider biodiversity. We are attempting to achieve the state of change ofbiodiversity. The first ofthese goals
conservation in aworldthat is living waybeyondits means, identifies particular species atrisk ofextinction; the second
andsotherapidlossofbiodiversity,especiallyatthespecies goalfocusesonusingthedataintheRedListformulti-species
level, should not surpriseus. analyses in order to identify and monitor trends in species’
status.
TheIUCN Red List Thediversityofspeciesonearthisextraordinary.There
It is very important to assess the health ofour global areanestimated8-14millionspeciesinexistence, 1.8million
ecosystemsbyprovidingup-to-dateinformationonthe state ofwhichhave been identified and described. The estimates
and trends ofwild species. The global tool for doing this is of how much of this diversity is being lost annually are
the IUCN Red List of Threatened Species (http:// disheartening, with the number of species assessed as
www.iucnredlist.org/). threatened increasing every year. By 2008, 44,838 (2.5%)
TheIUCN RedListCategories andCriteria(seehttp:/ species had been assessed (Fig. 1), of which 869 (2%)
/www. iucnredlist.org/documents/
have been classified as Extinct or Extinct in the Wild and
redlist_cats_crit_en_vl223290226.pdf)arewidelyaccepted 16,928(38%)classifiedasthreatened.Althoughonlyasmall
as the most objective and authoritative system available proportionoftheworld’sspecieshadbeenassessedby2008,
for assessing the global risk of extinction for species this sample indicates the serious conservation status ofthe
(Lamoreux et al. 2003; De Grammont and Cuaron 2006; species looked at so far, how little is still known and how
Rodrigues et al. 2006; Mace et al. 2008). Each species urgent the need is to assess more species.
assessed is assigned to one of the following categories, Despite the limited number of species assessed in
Extinct, Extinct in the Wild, Critically Endangered, relation to the total number of species known, and the
Endangered,Vulnerable,NearThreatened,LeastConcernand significant numberofData Deficient species included in it,
DataDeficient,basedonaseriesofquantitativecriterialinked the RedListisstill thelargestdatasetofcurrent information
J. Bombay Nat. Hist. Soc., 106 (3), Sept-Dec 2009 231
THE EXTINCTION CRISIS: FACTORFICTION?
11%
Fig. 1: Numberofspecies appearingon each published
IUCN Red Listsince 2000 Fig. 2:The status ofAmphibians by IUCN Red Listcategories
EX=Extinct; EW=ExtinctintheWild;CR=CriticallyEndangered;
EN = Endangered; VU = Vulnerable; NT = Near Threatened;
ontheconservationstatusofspecies.Completedandongoing LC = LeastConcern; DD = Data Deficient
assessments include the following: BirdLife International
bird assessments (updated 5 times since 1988); Global
Mammal Assessment (completed in 2008, now being
Statusofbirds
updated);GlobalAmphibianAssessment(completedin2004, BirdsarethebestknowntaxonomicgroupontheIUCN
now being updated); Global Marine Species Assessment Red List. Since 1988, there have been 5 comprehensive
(ongoing); Global Freshwater Biodiversity Assessment
assessmentsofbirds, withthemostrecentassessment, ofall
(ongoing);andGlobal ReptileAssessment(ongoing).There 9,990 known species, being completed in 2008. Less than
arevariousplantandterrestrialinvertebrateassessmentsthat 1% of bird species on the 2008 IUCN Red List have
have also started and which are gathering speed. insufficient information available to be able to assess them
beyond DataDeficient.
STATUS OFTERRESTRIAL BIODIVERSITY
Comprehensiveassessments,coveringeveryspeciesin
ataxonomicgroup,havenowbeencompletedforamphibians,
birds, mammals, cycads and conifers, warm water reef-
forming corals, freshwater crabs and groupers. They are
almost complete for sharks and rays, mangroves and sea
grasses.
StatusofAmphibians
Nearly one-third of the amphibian species (32.4%)
aregloballythreatenedorextinct,representing2,030species
(Fig. 2). Thirty-eight species out ofthese 2,030 species are
considered to be Extinct (EX), one is Extinct in the Wild
(EW). Another 2,697 species are not considered to be
threatenedatpresent,beingclassifiedintheIUCNCategories
of Near Threatened (NT) or Least Concern (LC), while
sufficient information was notavailable to assess the status
Fig. 3: Thestatusofbirds by IUCN Red Listcategories
of an additional 1,533 species (Data Deficient (DD). It is EX=Extinct; EW=ExtinctintheWild;CR=CriticallyEndangered;
predicted that a large proportion of these Data Deficient EN = Endangered; VU = Vulnerable; NT = Near Threatened;
species are likely to be globally threatened. LC = LeastConcern; DD= Data Deficient
232 J. Bombay Nat. Hist. Soc., 106 (3), Sept-Dec 2009
THE EXTINCTION CRISIS: FACTOR FICTION?
It is clear, however, that being well-studied does not STATUS OF FRESHWATER BIODIVERSITY
provide immunity from decline and high extinction risk.
Morethan 1 in8birdspecies(13.6%)aregloballythreatened IUCN is working with a number of partner
or extinct, representing 1,360 species (Fig. 3). Of these, organisationstofilltheinformationgaponfreshwaterspecies.
134species(1%)areextinct,4speciesnolongeroccurinthe Thisisbeingaccomplishedbyconductingassessmentsofall
known species within the following priority groups:
wild, and a further 15 are Critically Endangered species
flagged as ‘possibly extinct’, making a total of 153 bird freshwater fishes, freshwater molluscs, dragonflies and
damselflies, freshwater crabs and selected aquatic plant
extinctions since the year 1500.
families. With the exception of the crabs, none of these
Although8,564bird species(85.7%) arecurrentlynot
consideredthreatened,835ofthese(8.4%ofallknownbirds) assessmentsisyetcomplete globally.
There have, however, been some comprehensive
are NearThreatened; the remaining 7,729 species are Least
regionalassessments,inwhicheverydescribedspeciesfrom
Concern.
a taxonomic group within a region has been assessed. This
Statusofmammals hasenabledtheidentificationofriverorlakebasinscontaining
Themammal dataonthe2008 IUCNRedListinclude the highest levels of species richness, threatened species,
5,488 species, 412 subspecies and 21 subpopulations. The restricted range species, migratory species and/or species
important to the livelihoods oflocal communities.
primary focus is, however, at the species level. This is the
second time that all mammals have been assessed, the first Thefreshwaterassessmentscompletedforeasternand
southern Africa have identified lakes Malawi and Victoria,
being in 1996 (Baillie and Groombridge 1996).
Of the 5,487 mammal species assessed, nearly one- the lower Malagarasi drainage (Tanzania), the Kilombero
Valley(Tanzania)andtheSouthwesternCape (SouthAfrica)
quarterofspecies(22.2%)aregloballythreatenedorextinct,
as containing some of the highest numbers of threatened
representing 1,219 species (Schipper et al. 2008) (Fig. 4).
Seventy-sixofthe 1,219speciesareconsideredtobeExtinct species (Fig. 5).
(EX),and2ExtinctintheWild(EW).Another3,432species
arenotconsideredtobethreatenedatpresent,beingclassified
in the IUCN Red List categories ofNT or LC, while there
wasinsufficientinformation available toassess the status of
an additional 836 species (DD). f M
X
«
Numberofspecies
0
7-13
14-24
25-49
—
0t 25i0 50i0 1.0i0K0ilometers Source:IUCN
Fig. 4: The status of mammals by IUCN Red Listcategories
EX=Extinct; EW=ExtinctintheWild;CR=CriticallyEndangered; Fig. 5: Distribution patternsof regionallythreatened speciesfor
EN = Endangered; VU = Vulnerable; NT = Near Threatened; freshwaterfishes, molluscs, odonates (dragonfliesand
LC = LeastConcern; DD = Data Deficient damselflies) andcrabsacross eastern and southernAfrica
J. Bombay Nat. Hist. Soc., 106 (3), Sept-Dec 2009 233
THE EXTINCTION CRISIS: FACTOR FICTION?
Freshwaterbiodiversityisbeingthreatenedbyanumber
ofkey impacts, including overexploitation, waterpollution,
river flow modification (including water abstraction),
destruction or degradation of habitats, and invasion by
invasive alien species (Millennium Ecosystem Assessment
2005; Dudgeon etal. 2006). Compounding these threats are
the predicted global impacts of climate change leading to
temperature changes and shifts in precipitation and runoff
patterns (Dudgeon etal. 2006).
Usingfreshwaterfishesasanexample,beingoneofthe
mostwidelyassessedofthefreshwaterspeciesgroups,thelevel,
nature and distribution of major threats can be identified.
Oftheregionsassessedsofar,theMediterraneanandMalagasy
endemic freshwater fish are shown to have the highest
proportionsofgloballythreatenedspecies,withmorethan50% Fig. 7: Summaryof2008 Red Listcategories
ofspeciesthreatenedineachcase,andsouthernAfricatohave forcompletedcladesofmarinespecies
thelowestproportion,with 17%ofspeciesthreatened(Fig.6). Numberofspeciesassessed in each group in parentheses
[black=EX; red=CFVEN/VU; yellow=NT; green=LC; grey=DD]
THE STATUS OF MARINE BIODIVERSITY corals, (seabirds, marine mammals and marine turtles). Work
onthesharksandraysisnearingcompletion.Theoverallresults
Inrecentyears, there hasbeengrowingconcern inthe of these assessments (including the preliminary results for
scientific community that a broad range of marine species sharks andrays) are shown inFig. 7.
could be under threat of extinction and that marine The threat status of the different taxonomic groups
biodiversityisexperiencingpotentially irreversible loss due variesquitewidely. Overfishingandincidentalmortalityare
tooverfishing, climate change, invasive species and coastal particularcommonthreatsinthesea.However,withthereef-
development(RobertsandHawkins 1999;Dulvyetal.2003). building corals, the situation is significantly different, as
In 2006, IUCN, Conservation International and Old describedbelow.
DominionUniversityinitiatedanambitiousproject(theGlobal The world’s known 845 species of reef-building
Marine Species Assessment) to complete IUCN Red List zooxanthellate corals (Order Scleractinia plus the families
assessmentsforagreatlyexpandednumberofmarinespecies. Helioporidae,Tubiporidae and Milleporidae) were assessed
ItisplannedtocompleteRedListassessmentsforover20,000 forthefirsttime(Carpenteretal. 2008).Thesereef-building
marinespeciesby2012.Muchprogresshasalreadybeenmade, corals provide the essential habitat formany species offish
and approximately 1,500 marine species have been added to andinvertebrates,makingthemthemostbiologicallydiverse
the 2008 Red List. IUCN has now assessed all ofthe world’s ecosystemsintheocean.Morethanone-quarterofthesecorals
known speciesofsharksandrelatives, groupers,reef-building (27%)havebeenlistedinthreatenedcategories,representing
anelevatedriskofextinction. Over20%ofspeciesarelisted
as Near Threatened and are expected to join a threatened
category in the nearfuture.
The primary threat to these reef-building corals is the
increasedfrequencyanddurationofbleachinganddiseaseevents
that have been linked to the increase in sea temperatures, a
symptomofglobalclimatechange(Carpenteretal.2008).These
impacts are further compounded by anthropogenic threats,
includingcoastaldevelopment,coralextraction,sedimentation
and pollution. Another further threat to corals is ocean
acidification as a result of increasing levels of atmospheric
%ofspecies carbon dioxide. This is reducing ocean carbonate ion
concentrationsandtheabilityofcoralstobuild skeletons.
Fig. 6: Proportionsoffreshwaterfish speciesbythreatcategory
in each ofthe regionsassessedcomprehensively. Globally,theIndo-Malay-PhilippineArchipelagoorthe
Onlyspeciesendemictoeach region are included ‘CoralTriangle’hasbyfarthehighestnumberofcoralspecies,
234 J. Bombay Nat. Hist. Soc.( 106 (3), Sept-Dec 2009
THE EXTINCTION CRISIS: FACTOR FICTION?
Percentage threatened species Source: IUCN
4.8 14 18 25 60 100
Fig. 8: Mapshowingthe percentagesofthreatened reef-building coral species acrossthe world
and also high percentages in threatened categories (Fig. 8). these two groups are markedly different in South America.
This region is also known as the epicentre of marine Although nearly one-third of amphibians are at risk,
biodiversityandhasthehighestcoralspeciesrichness.Coral threatenedamphibiansarefoundtobeconcentrated in afew
reefsin theCaribbeanregionhave beenimpactedbyrecent, areas only, especially in Mesoamerica, the northern Andes
rapid population decline of 2 key species: Staghorn Coral andtheGreaterAntilles. Conversely,mostpartsoftheworld
AcroporacervicomisandElkhomCoralAcroporapalmata, have at least 1 threatened bird species, despite the fact that
both ofwhich have been listed as Critically Endangered. In only 12% ofbirds are threatened.
any region, the potential loss ofthese coral ecosystems will
have huge cascading effects for reef-dependent species and LOOKINGAT A FINER SCALE
for the large number of people and nations that depend on
coral reefresources foreconomic and food security. The Red List criteria were developed for use at the
globalscale,atwhichtheentiregeographicrangeofaspecies
GLOBALTHREAT PATTERNS is considered. However, IUCN is increasingly undertaking
regional Red List projects. Regional and national lists are
Closerexaminationofsomeofthesetaxonomicgroups usually country-led initiatives and are notcentralised in any
reveals interesting patterns inthegeographicconcentrations way; they differ from each other widely in terms of scope
ofthreatened across the globe. Fig. 9 shows the geographic and quality but can be very useful in guiding conservation
patterns generated from overlaying the distributions of all work at subglobal levels.
threatened species in 4 taxonomic groups (birds, mammals, In the Mediterranean region, for example, IUCN has
amphibiansandcorals).Thecontrastbetweenthetaxonomic assessedtodatethefollowingtaxonomicgroups: amphibians,
groups demonstrates that geographic patterns of threat for reptiles, birds, mammals, sharks and rays, freshwater crabs
one group do not predict the patterns of threat for another andcrayfish,endemicfreshwaterfishes,anddragonfliesand
group; hence the importance ofassessing the statusofmany damselflies(hereafterreferredtocollectivelyasdragonflies).
groups ofspecies. Overall, the proportion of threatened species in the
Thereareimportantconcentrationsofthreatenedbirds Mediterranean (those classified as Critically Endangered,
and mammals in South-east Asia, but the threat patterns of Endangered or Vulnerable), either at the global or regional
J. Bombay Nat. Hist. Soc., 106 (3), Sept-Dec 2009 235
THE EXTINCTION CRISIS: FACTOR FICTION?
Threatened coral richness
1 26 58 98 143 176
Source: IUCN Red List ofThreatened Species
RL Categories: Vulnerable(VU), Endangered (EN), Critically Endangered(CR) TOHfETIVUWCENATREENDELDISSTHOES'
Fig. 9: The geographic patterns generatedfrom overlayingthe distributionsofallthreatened species in fourtaxonomicgroups
(birds, mammals, amphibiansandcorals)
level, is about one-fifth (19%), and about 1% ofthe species to identify key regions and taxa that require greater
are already extinct in the region. These percentages will be conservationattention.
higherifsomeofthe currently DataDeficient speciesprove Thisapproachtakesarandom sampleof 1,500species
to be threatened, as is likely tobe the case. fromdifferenttaxonomicgroups(Baillieeta/. 2008).Itallows
Freshwater species have been mapped based on river theidentificationofthegenerallevelofthreattoeachgroup,
basins flowing into the Mediterranean Sea and adjacent the mapping of areas likely to contain the most threatened
AtlanticOceanriverbasins. Fig. 10indicatesconcentrations species and the identification ofthe main drivers ofthreats
ofspecies at risk, in particular in the Iberian Peninsula, the and helps pinpoint what key actions are required to address
Balkans,thewesternpartofGreeceandtheareafromTurkey declines in the group as awhole.
down to Israel and the Palestinian territories. The results of both the comprehensive and sampled
assessments are starting to provide new insights into our
BROADENINGTHE COVERAGE OF understandingofthestatusoftheworld’sspeciesthatcanbe
BIODIVERSITYASSESSMENTS built upon to track changes over time. The current plans to
expandthenumberofspeciesassessedfortheRedList,using
A new initiative is being employed to broaden the both comprehensive and sampled techniques, will, when
taxonomiccoverageoftheIUCN RedListinordertoenable implemented, increase the numberofassessed species from
a better understanding ofbiodiversity status as a whole and 45,000 (on the Red List in 2008) to 1,30,000 (Fig. 11).
236 J. Bombay Nat. Hist. Soc., 106 (3), Sept-Dec 2009
THE EXTINCTION CRISIS: FACT OR FICTION?
Fig. 10: Species richnessofthreatenedfreshwateramphibians, crabs, endemicfishes, mammals, dragonflies and reptiles
inthe Mediterranean basin
ThefirstresultsofthesampledapproachtoRedListing BIODIVERSITY
are now becoming available, specifically for reptiles and
fishes, forneitherofwhich the comprehensive assessments
Vertebrates Invertebrates Plants
are complete yet. Across reptile groups, for example, the
IE
proportionofspeciesthreatenedvaries: 43%ofcrocodilians f ^ 1 ^
are threatened, compared with 12% of snakes and 20% of Mammals Ants Bryophytes
Birds Butterflies Pteridophytes
lizards. These patterns are likely to reflect differences in Reptiles Dragonflies Gymnosperms
geography,rangesize,habitatspecificityandbiology,aswell Amphibians Freshwater Molluscs Monocots
as threat intensity. Indo-Malaya is the most species-rich Fishes Freshwater Crabs Angiosperms
biogeographic realm forreptiles, and it also has the greatest Sharks Reef-forming Corals ^ Fungi y
density ofthreatened (CR, EN andVU) species (Fig. 12). t Dung Beetles
Crayfish & Lobsters
There are also some early results from this sampled Cephalopods J
approach for invertebrates. A map of the distribution of
threatened freshwater crabs and dragonflies reveals some
centres of threat for freshwater systems (Fig. 13). Marked Fig. 11: Overview of IUCN Red Listassessments:
comprehensivelyassessed by2008 (black);
concentrations of threatened species exist in Vietnam, comprehensiveassessments underway(red);
Thailand,Cambodia,MalaysiaandthePhilippinesinSouth- statistically random samples planned orunderway(green)
eastAsia; Sri Lanka and the Indian Western Ghats in South
Asia,andColombiaandMexicoincentralandSouthAmerica. the long list of unique species that have been lost forever.
These patterns are heavily influenced by the distribution of Understanding the extent of recent extinctions provides
restrictedrange species. insights into historic extinction rates, which in turn can be
compared to the rates over geological time to determine if
EXTINCTIONS current trends are normal or acause forconcern. An insight
into the process of extinction can help us identify species
The global extinction of a species usually represents that are at a risk of extinction and enable us to highlight
an end point in a long series of population extinctions. taxonomicgroupsorspeciesfromspecificregionsthatareor
Creating an inventory of recent extinctions helps highlight will be particularly prone toextinction.
J. Bombay Nat. Hist. Soc., 106 (3), Sept-Dec 2009 237
THE EXTINCTION CRISIS: FACTOR FICTION?
)
0^
Proportion of species assessed as tmhreatened Source: ZSL& IUCN
0.11 0.12 0.33
1
Fig. 12: Threatened species richness mapforreptiles, based on a random sampleof 1,500 species, 244ofwhich arethreatened
a timm - -%' >
.
Proportion of species assessed as threatened Source: ZSL& IUCN
™
^^ ^^^
T
0.02 0.08 0 28 0
.
Fig. 13:Threatenedspecies richness mapforfreshwatercrabs (n =210species), anddragonfliesanddamselflies (n= 136species)
238 J. Bombay Nat. Hist. Soc., 106 (3), Sept-Dec 2009
THE EXTINCTION CRISIS: FACTOR FICTION?
o
<*> o # •
cP
•
• Reptiles
• Mammals
• Birds
• Amphibians
o Molluscs
Fig. 14: The distribution of Extinctand Extinct in theWild reptiles, mammals, birds, amphibians and molluscs
The world’s list ofdocumented extinctions continues degradation and conversion (resulting in particular from
to rise. The 2008 Red List includes 804 species listed as agriculture, logging and residential and commercial
Extinct and 60 Extinct in theWild. In the last 24years there development), overexploitation, invasive species, pollution
havebeen29documentedextinctions,withrecentextinction and, increasingly, climate change (Figs 16, 17, 18).
rates exceeding those from fossil records. With current Habitat loss and degradation are by far the greatest
extinction rates 100to 1,000times the natural (background) threattoamphibiansatpresent(Fig. 16),affectingnearly61%
extinction rates, it is likely that the world is experiencing a of all known amphibians (nearly 4,000 species), including
net loss of species, perhaps for the first time in millions of 87% of the threatened amphibian species. The next most
years (Baillie etal. 2004). common threat to amphibians is pollution, which affects
There are major differences in the extinction patterns aroundone-fifth(19%)ofamphibianspeciesoveralland29%
between the five taxonomic groups mapped in Fig. 14. Bird of threatened species. Although disease is a less common
extinctions are overwhelmingly biased towards oceanic threat, it is much more likely to make a species globally
islands (including New Zealand), whereas the largest threatened (Fig. 16). Indeed, the fungal disease
concentration of mammal extinctions is in Australia.
DocumentedamphibianextinctionsarefocusedonSriLanka,
but this might be an artefact ofunder-recording extinctions
elsewhere. Mollusc extinctions are concentrated in North
Americanriversystems,possiblyanotherrecordingartefact.
Adetailed examination ofbird extinctions since 1500 A.D.
indicates that the pattern ofextinctions might be changing.
Although more than 80% ofbirds are found on continents,
allextinctionspriorto 1800occurredonislands.Thispattern
has started to change in recent years, with more extinctions
occurring on continents (Fig. 15).
THREATS
Year
The major processes threatening species and driving Fig. 15: The numberof bird extinctionsthat have occurred
extinctionsareallofanthropogenicorigin,andincludehabitat on islandsand continentssince 1500A.D.
J. Bombay Nat. Hist. Soc., 106 (3), Sept-Dec 2009 239
