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About Island Press Saving a Million Species EXTINCTION RISK FROM CLIMATE CHANGE Since 1984, the nonprofit Island Press has been stimulating, shap ing, and comm unicating the ideas that are essential for solving envi Edited by Lee Hannah ronmental problems worldwide. With more than 800 titles in print and some 40 new releases each year, we are the nation's leading publisher on environmental issues. We identify innovative thinkers and emerging trends in the environmental field . We work with world renowned experts and authors to develop cross-disciplinary solutions to environmental challenges . Island Press designs and implements coordinated book publication campaigns in order to communicate our critical messages in print, in person, and online using the latest tech nologies, programs, and the media. Our goal: to reach targeted audiences-scientists, policymakers, environmental advocates, the media, and concerned citizens-who can and will take action to protect the plants and animals that enrich our wo rld, the ecosystems we need to survive, the water we drink, and the air we breathe. Island Press gratefully acknowledges the support of its work by the Agua Fund, Inc., The Margaret A. Cargill Foundation, Betsy and Jess e Fink Foundation, The William and Flora Hewlett Foundation, The Kresge Foundation, The Forrest and Frances Lattner Foundation, The Andrew W. Mellon Foundation, The Curtis and Edith Munson Foundation, The Overbrook Foundation, The David and Lucile Packard Foundation , The Summit Foundation , Trust fo r Architectural Easements, The Winslow Foundation, and oth er gen erous donors. Th e opinions exp ressed in this book are those of the ,lllllI or(s) and do not neces sarily reflect the views of our donors. 2012 o ISLAND PRESS Wlr ~/lil(I//{J1I 1( :11111 '/11 1/ ,lIlItiml Chapter 11 Quaternary Extinctions and Their Link to Climate Change BARRY W. BROOK AND ANTHONY D. BARNOSKY Millennia before the modern biodiversity crisis-a wo rldwide event I'i"ing driven by the multiple impacts of anthropogenic global \ 11:lnge-a mass extinction oflarge-bodied fauna occurred. After a mil 111'11 years ofsevere climatic fluctuations , during which the earth w(L'(ed ,!lId waned benveen frigid ice ages and warm interglacials, with appar 1 'ild y few extinctions, hundreds of species of mammals, flightless l lil'd s, and reptiles suddenly went extinct over the course of the last " O,()()O years (Barnosky, 2009) . Due both to our intrinsic fascination \\'i iii huge prehistoric beasts and to the possible insights these wide "III '\':h.l species losses might lend to the modern extinction problem, rill' Ill ),stery of the "megafaunal" (large animal) extinctions have led to 1IIlI vil ri1wrizing, modeling, and digging (for their fossils or environ 111,'111:11 proxies) over the last 150 years (Martin, 2005). The topic " 'll linllt:s to invoke strong scientific interest (Koch and Barnosky, ' (l()(, ; Cr,lyson, 2007; Gillespie, 2008; Barnosky and Lindsey, 2010; ~ J I 'I 'I II\; ,~ - lklVO et ,)1., 2010; Price et al., 2011). III Ihis dl:lpt<:r, we t(>ClI S on recent work that explicitly considers il l!' I'~' LII ive ruk of !'larur:)1 climate change compared to nonclimate 111 111 1.111 c:ll.Isc.'d l'i1n::II'c.·nillg processes (stich as habitat loss and hunt 1111\ ) ill Iki vill!'; 1'1ll' IIH')l,:ll:lIll1 :11 nrilll'liuns, Wl' heg in with a short I' \ I' IV c ,i' I hI' )',Iuh,d p.IIII'I'1i I)t' (~II :II'l'rl1 , 1 ry l'X I'i n~' 1 iOlls and Sill 1111) :1 I I I '1'11111 ' 1',\'III'I ';d 11'.I'it 'II', wllv 1.11'1'." ,lIlilll.l1.<: IlIi),:,hl ill' 1' , lIli ~' ld : ll'i )' I ~" V 1-- IHO EVIDENCE FROM THE PAST vldn t:rable to direct human impacts and climate change. We then ex IIII II'L' how the pattern of megafaunal extinction corresponds to borh II\I' chronology of human expansion and climate change and their pro /('\ Inl impacts. Taken together, this body of information leads us (0 t 't IIld IId t: that climate change alone did not drive the mass extinctioll 'II 1.1Il" Quaternary megafauna, but overlain on direct and indirect htl 111.111 ,IClioIlS, it exacerbated overall extinction risk tremendously. Thl' 1.1 1l( ' IIIIIIIC message is that the synergy of fast climate change wil'h III' 'I I' dirclT human impacts can have particularly fatal consequencl'~ ',ll III.III,VIionhuman species-and this is particularly true today, wh~'1l 111 1111.111 ildhl L'IlCeS, including climate disruption, are so dramaticallv ,',II ,11"1 111.111 I'hcy have ever been in the past. Quaternary Extinctions and Their Link to Climate Change -40kyr ~ 1>'/ \ 4' 2' ~~--:-i"~~~] 1 17· 11.5 2 1 13.5 kyr ~ 3P/ \ 181 15 ISO. 13 f lcyr I~i= 11 .C~1 Holocene 11\ 5. 3 ~<~:rJ '3' ' . \ ~Jj~locene I , .0i!~. 6 -r ~' I ~O~72.44k kyr II 51'~O -- II __ yr I I'~x t incri on and Vulnerability ofMegafalma t/ / > 16 1? 4q .28 I..... ------' 1'111' "lid () II.III.: nLlry (late Pleistocene and Holocene) die-offs COI11 I" 1,', ('..1 ,I :,i}'.lIi1i ~' : 1I11" g lobal mass extinction event, which led to the eli III 11 1,11 11111 ,II h.dt' lit' :111 mammal species heavier than 44 kilograms (100 I" 1111,,1:,) ,llleI 1I1 'II~T brg<.:-bodied fauna across most continents (Au., I, ,lii,l , I ':"":I.,i :l, Norl"ll alJd South America) and large islands (West I II cI 11',', , M,ld,I).!,:ISI\lr, alld N<.:w Zealand), between 50,000 and 600 ye:ll" 1"" 11 ,1 ' 1"\"'("111 (Koch and Barnosky, 2006). The losses included large 111.1111111:11., (L·.g., mammoth, genus Mammuthus), reptiles (e.g., gialll l' I" lIeI:, ~; lIdl :1., MCJla /t,lnia), and huge flightless birds (e.g., New / ,(',1 1.11111 111'1 :1:lIId Ausrralian Genyomis). In Australia, around fifty spccic.\ , lilt Ilid i1I,l!, rli inoceros-size wombats, Short-faced kangaroos, and pr<.:d,1 I, 'I I' I" I.'ISI II IlS disapp<.:ared (MacPhee, 1999). In North America, 1'111 el l"llll Inll was SOI11<.: sixty species of large mammals plus the laq.!,('hl l, il'e1:: ,lIld !"orroiscs, and South America saw the disappearance o( .11 1('.1',1 ,~ix l y·six Iarg<': -Jl)<1111maJ species. Eurasia and Mrica were less 1I.1le! Ii ii, 1'"1 II I,'Vl'l'I'hc!t.:ss saw major losses in their large-mammal faulI:! , Id " "'11 ,lIld 8<.:vcmet;n specics, respectively. Region by region, these n 1i,It lin ll I,'VCllrS f()lIowni within a few centuries to a few millenlli:1 IIIi 11" 111 di8pL'rS :11 or 1-l00'YUlsapiens to new lands, and wne parricularl y :W 1'1 '1(' IV hl'lI Iht;y We re also <.:l1twined with changes in rhc n.:g ioll :" ')I 1,.II ,b:II l'Iill1:lI~' SY.'I~l'lJ l (fig. II - I ). SCI IV".II W. IS Ih l ' 1..':11 IS:" IIlCCh:lIIisll1 hdlind dll's(" eX Iilll'l inns \ I, 111"1, ,, 1111111:111.'" Ill' hlll 'h? The drivers 11f'I,il"il ('xlililliIIIlS, P:I:;I ,lilt! l ' I" ~t' lll . ,Ill' 'lfi "11 '~ lIq1J'i.':i ll!,,Iy din illill I" I,ill '.I"IVII (Nit I\i llll\ 1'. fi nu608 of extinction Moslly Human Moslly Climale InsuHicient data Relative size of extinct Correlations in time Numbers indicate how taxon icon corresponds many genera have robust to relative magnitude of L oJ Humans arrive dating control evidence extinction. Number of except as indicated: • Climatic change extinct genera is listed Provisional evidence on each icon. ? Needs more work -, I I ' Ie 11(/, JT-I. Late Quaternary megafaunal extinctions, human hWlting, and di lilol lt' ( /lange on the continents. The dashed box indicates the credible bounds of IIi, I IrsI' arrival of modern people, Homo sapiens sapiens, with the best estimate ad i'" , ' III In the human figure (the latest estimate for Australia is about 48,000 years III" I ky r BP]). Substantial climate change events, predominantly the last glacial Iii 1\ il I IlIlI1 ,lnd Holocene warming, are indicated by gray shading inside boxes. " !III' (' : K.och and Barnosky, 2006. 1'1 1),/ ), hut plausibly include: (i) being outcompeted by newly evolved II I Illv;tsive spccies; (ii) failing to adapt to long-term environmental , I101 II }',l' (e .g. , climatic shifts); and (iii) reduction in abundance caused 11\ 1,IIIdpm disturbance events (e.g., epidemics, severe storms) with a IIi "wl/lIl"m bilur<.: to recover to a viable population (Blois and Hadly, '( 1)')), !\ C()llJlllOllly cited g<': llcralization is that larger-bodied verte 1".1 11" , (w il'll I'he L'xtrctne rccwr t()rm being the Quaternary mega 11111101 ) .11'1' 11101'1.' eXt'illCrio/1 -prone I'h;lIl smaller bodied ones (Bodmer I I ,iI , 1')')7: McKi'lIH'Y , II)()?). I\n ':IlISl' hody sizc is inversely corI I,'oj I'd Willi 1'"1,"1.11 i,,, I ",iI,\" 1.11'/',1' h, It lit'd .lIlirn:lls rL' nd ro h<: kss 11\ 1 Quaternary Extinctions and Their Link to Climate Change EVIDENCE FROM THE PAST .11 IIIlld :1I1r and so more intrinsically vulnerable to rapid change and de Illographic disruption. Indeed, when armed with some knowledge of ('llIpiridly well established biological scaling rules (allometry; Da 111111 h, 1981), such a hypothesis makes a lot ofsense. Large-bodied an III 1.1 Is such as elephants or whales produce only a few, precocious off 1'1 'I'illg, but invest substantial resources into their care. This life-history :;II.IIl'!'\Y kads to the death of juveniles being a major demographic set I•. Ide ()II a population-wide basis, even an apparently small additional 1.-,,1'1 chronic mortality can result in rapid declines in abundance .llld , within a few centuries, a collapse to extinction (Brook and John :.(111 , 2()()6; Nogues-Bravo et al., 2008). The extinction proneness of I.II,}"C bodied animals is further enhanced because of other correlated 11 .lil s such as their requirement oflarge foraging area, greater food in 1.1"(" high habitat specificity, and lower reproductive rates (West and I ~i'( 'WII, 2(05). Why thcn (in evolutionary terms) be big? Three reasons are that I.II'~\(' ~\llil11al s arc long-lived (so have multiple attempts at reproduc Iic '11), have relatively better heat regulation and water retention than ';111.111 .lI1inJais, cmd have lower predation rates, especially when herd III)',. Their size protects them from all but the biggest predators, thcy 11 .11It' :1 great capacity to ride out hard times by drawing on their fat re ·.C·I \Irs, rhc)' can migrate long distances to find water or forage, and t1lC' y L'all ()pt not to reproduce in times when environmental condi II. 'IIS .IIT unt:1vorablc, such as during a drought (Brook et al., 2007). I'IIIIS ill I'he majority of circumstances, being big is good, because il .IC I~ .IS .1 demog raphic buffer. Indeed, such ecological specializatioll I. '11i Is Ic. evo lvc repeatedly because, in relatively stable environments, '~ I '1 ' 1 I.llisl species tend to be better than generalists at particular narrow 1.1.·.k::. Ilmvevt:r, when an envirorunent is altered abruptly at a rail' .11 II . " " lie )l'In:11 b:Kkgrollnd change, speciallst species with narrow cco I. 'I',Ic .11 j\l'l'It:n.: nl:cs bear the brunt of progressively wlfavorable contli II, "I S Sll l' h as habitat loss, degradation, and invasive competitors (ll I'II" 1.11 III'S ( B:lllllf'(lrd, 1996; Harcourt et al., 2002). An extremc CVC: III , 'III, It : I.~ :1 holid e strike tt'OI1l space (Haynes, 2008) or an inrclligC: III, "" "'1" l1l , w Ic:lding bipedal ape (Martin, 200:;), tbar also widely allrl" 1.I IIoI",,·:IPI:S by pracrices such ,IS burning and farming, can be rbc; k vc'l 111.11 IIIIIJillgl.·S Illl' upl"ill1ality ofrhis r(:gu larly evo lved srrat(:gy o/'l :lI l',c hunted by invading prehistoric people in Pleistocene Australia, arbo real (tree-dwelling) species occupying closed forests suffered far fewer extinctions than saVaru1a (grassland) species, and of the latter group, tbose with high per capita population replacement rates (e.g., grey kangaroos; Macropusgiganteus) or the ability to escape to refuges such as burrows (e.g., wombats; Vombatus ursinus) were best able to persist (Johnson, 2005). 0" I"" Iy . , i'I.I·. III ' I'IH' ,·ll viI'Clnllll·1I1.l1 (,()III~'XI : lI11II Y P~·I)t'II\1'( · .11 .1I ,~ c) IIdps di ('t.II l' ,III I\"~ I)IIII I;(' Ic. dl.lll1\(· CII IIl) VI· 1 I.II·C··.·,,'I ·. l:clI illl·:I.IIIlI" WIIl'II 1'..11 Ii.';) 11 \ 183 The Role of Human Arrivals During the last 100,000 years, modern humans have spread across the world from their center of origin in Africa, reaching the Middle East by 90,000 years ago, Australia by 48,000 years ago (based on tlle most s(:cure evidence presently known, Gillespie et al., 2006), Europe by 40,000-50,000 years ago, SoutllAmerica by 14,600 years ago, NOrtll America by 13,000 years ago, most of the Pacific Islands by 2,000 lears ago, and New Zealand by 800 years ago. (For dates estimated by radiocarbon dating, the radiocarbon age is calibrated to calendar I(:<lrs.) This wave of human dispersal was likely to have been medlated hy climate change: a wet penultimate interglacial probably encouraged 111(: spread of early Homo sapiens out of Africa, and in the Northern Ilcmisphere, end-Pleistocene immigration into tlle Americas was fa ,ilirated by glacial ice sequestering water and lowering sea levels, which in turn exposed a land bridge between Eurasia and North \ l1l erica and opened coastal migration routes. At the very end of tlle I'ki stocene, it was global warming that melted ice and opened an ice II'n : CI)rridor through central Canada for a wave of Clovis hlUlters. A striking feature ofthe megafaW1al extinctions is tllat, in every ma l' '1 ' Illstance where adequate data exist, the extinction follows the first Ill'i v:d of people on a "virgin" continent or large island within a few 111111l11'(:d to a few thousand years (fig. 11 -1). This point is further un 1I" I':K'(lred in figure 11-2, which shows the short overlap period for well 1,I 1(',llllc!4aflllnal remains and archeological artifacts, in New Zealand, r~ I '1111 America, and Australia, based on the latest dating and sample se I, , Ii, III protocols (Gi llespie, 2008). (Note the different time scales on 11.11 1o ·IN1\ , B, and ( :- rh(:se three (:vents wcre not synchronous in time.) I 111 111 idene\.· :donl' is nor sulri(iC:1l1 evidence for causation, but this conI'" 1'111 Y.11 IhI' vny k.I .~ 1 1)1'( )vil k s sl)'( 1I1g L'irCIln1Sr:111rial support for the ,I 111.11 .1 1111111.111 pn':"'111 (. \V.I .'; .1 lit ·, ' ·S.~ .II'V pl'rc 'l )nd iI ion 1;)1' :H.'(I.; lc:rar~·d It " IH4 Quaternary Extinctions and Their Link to Climate Change EVIDENCE FROM THE PAST A,_ ~ Rattus exulans = & rat-gnawed seeds -==== Moaeggshell 1 ~ooo New Zealand 1500 1000 500 0 -500 -1000 -1500 -2000 -2500 Calendar Age (years caiAO/BC) B ~ Clovis-age ~ Archaeology ~ i ~ . Mammuthus Smilodon fatalis & Canis dirus - North America ~ 10 15 20 25 30 35 Calendar Age (ka calBP) c ~ - Archaeology 1·e charcoal indirect OSL 185 fauna, We are a species that broke a fundamental ecological rule: large predators and omnivores are typically rare (Tudge, 1989), A recent analysis by one of us (Barnosky, 2008) has shown that in achieving eco logical dominance, a rising biomass of people ultimately and perma nently displaced tl1e once-ablmdant biomass of megafauna, The point, well illustrated in figure 11-3, is that when the species richness ofmega fauna crashed to today's low levels, their equivalent total biomass was replaced by one species (Homo sapiens), Indeed, we surpassed the nor mal prehistoric levels of megafaunal biomass when tl1e Industrial Rev olution commenced, and now, when combined with our livestock, vastly outweigh the biomass ofmammal faunas of the deep past- an ex plosion of living tissue supported primarily by the use of fossil energy (which, for example, makes it possible to produce and distribute inor ganic fertilizers), The energetic trade-off between a large human bio mass (lots of people) and a large nonhuman biomass (lots ofother spe cies) demonstrated by tl1is Pleistocene history has a dear conservation implication: to avoid losing many more species as the human popula I'ion grows in tl1e very near future, it will be necessary to formulate poli cies that recognize and guard against an inevitable energetic trade-off at the global scale, The pressing need is to consciously channel some mea sure of natural resources toward supporting otl1er species, ratl1er than Extinct megafauna direct CSUS-ESR & "c gelalin • Megafauna Loss vs, Global Human Population Growth • C/) Q) '1:; Q) Q. Australia 400 (/) :'(1 30 35 40 45 50 55 60 65 70 75 80 85 90 - Americas .... , :;:J 300 ~I ~I f"'" 1ii Ol Q) Dating data on human-megafauna overlap in New Zealand (A) , N III 'I h AnH.:ri ca (B), and Australia (C), The dates are stacked from youngest (t'ol' ) I,. ,.1. il-SI (htIITom) for the archeology (dark shading) and oldest (top) to young<"" (I" 'lit lIll ) li)/' Ihe animal remains or proxies (light gray shading), Bars rcprt'S"11i ,jdtilll\ IIIh:crr:lillfies, SOl1l'ce: Gillespie, 2008 (includes detailed legend), ... .--.. 350' - III 1I11 I I1I U , 11 - 2 , Eurasia Beringia Australia III c:: Calendar Age (ka) 1 q' 250 ::2 200 '0 150 ..0 ill 100 E ::l 50 Z oB It) 100,000 ~ t " ~ It) ~ 10,000 14 12 0 X c:: 10 0 8,0 :-§ 6,0 4,0 2,0 0,0 :;:J Q. 0 (L • 1,000 Years before Present the evidence that mo~ t o( 11 II slirvi v<.:d through pn:vioLls, <.:qll:lll y pronounced Cli vi 1'1 III 111('1\,11 :1111):11 l: Xrin <.:tioI1, l:spc<.:iaJly given " XI illl' l I.IX :I 1/1\' 111.11 Ill'l'llIrh : II' ioll,~ bd(lI'(': /\ f'llIlIwi' IiiII' 1i1(' I',I"I>,1I oj' hum:uls :uTi vnl. illdin:cl l'vidl'Il\\ ' \ 'III1I\ ' ~ 1 11'1)111 ,l.~,~rssill!-!- Il ,t 11 11(1, 1/-3, Dcclinc in gloh:l1111l'gaEllma hiodiversity (number of species; light 1\1,1\' ) l'l't.: r rh t.: i:l~r g I:Ki :ll - ill,.,: rgl :l c i ~ 1 cyrle, plottl'd against tbe increase in world i'''11111.11 i(lll jOlllllv l 'i N( ' ill 1111111.111 :lhlllld,lIh '\' ,\lld 1111 ' 1'"' \ 11'IIIIII ,' :III,'il' "I"III1 T ,,1 , 11, '.1 ,~i 'l.t' (11'1/011-10 .l'11/,ir'll,I , I 'y .I :II 'k )',1':1)' ,II'I'IIW::' II'"II" lIkl', ./,OOH , ",I 1\1\.11111' l'Xlill\:I'ioll ev e l1t~ by (;t)ntincllt arc indi 1'111 "10'1.111.111 oi' Y" :II'S hdc Irc p/'l';,~l'I'lI') ,so\lrce: I H(l Quaternary Extinctions and Their Link to Climate Change E V IDE NeE FRO M THE PAS T ,~ e lldy toward humans, for example, in the form of enhanced sustain :Ihk farming practices and stepped-up efforts to protect and expand ex iSI ing nature reserves. Also critical will be developing alternatives to l,~sil fuels for the energy that currently sustains the global ecosystem, " ~ IIL' c iall y humans, so far above its pre-anthropogenic level of mega 1.11111:1 hiomass. Iluman impacts on late Quaternary enviromnents were many and \'.Iried (Barnosky et aI., 2004; Lyons et aI., 2004a). The role of prehis I'll'i( pcople as hunters of big and small game has been reviewed ex Il'Ilsi vdy (Martin , 2005; Surovell et al., 2005; Grayson, 2007); meat IV.IS (learly a component of the hunter-gatllerer lifestyle (Bulte et al., '()()(l), blll killing may have also occurred for reasons beyond subsis 11 '111 I ' (eg., hunter prestige). Beyond direct predation, however, hu 111,,"': ~lT llI ro have stressed megafauna by burning vegetation on a 1.11 II I ~I ,Ipl' Sl':lk (and in doing so, perhaps radically altering local di III ,I!! ': Milln ct :Ji., 2005) and by introducing commensal species such pi" 01 11 )', ," (I:inkl, 2005), rats (Duncan et al., 2002), and disease (Lyons C', ,II , , W()/I,h). Ovcrkill, the hunting of a species at a level sufficient to ,It iV(' il 1'1 nl ill(\ ion, with or without an additional pressure from fac Ie 1\", ,'''H' I! ,IS hahirar modification and clin1ate change, has been shown \1,111'.1 vi,lhle killing mcchanism for megafawlal species (fig. 11-4) if' II H ' 1111111 CI'S :t1so could LIse other species when they deplete the original 1.11 ,)',1'1 speci<.:s Ixlow viable ablmdances (Bodmer et al., 1997; Alroy, I()O I, Bruok and Johnso n, 2006). 1000 N idlc' Illodding indicates strong correlation between specific climale V;II 'i.lhk·s and spccies distributions (Hijmans and Grallam, 200() : NeI) ',III'S Bra.vo ct ai. , 2008 ), and it now seems clear that climate i ,~ ,I k('y d rlC rtllill ~lIlr of whether or not a species can exist in a given 10Clk , 111.':1 likl.: hUll1an imp:1cts, climatic impacts on species are direct and ill tlil ~'I. I , Direcr impacrs incilide exccedin~ physiologically imposed rnll 1'1.'1',1111 1'<.' :t llli prn:ipirarioll limits on a species, such as criticalrc.:mpcl,1 1111 '(' I I! r',,'sII 0 Ids li)r J1lllsk oxen o r pikas, whieh have limited heal'-lo!,,'1 ,Ihilil i('s, Il1Ilil'l': l'l' irnpa (t~ incilidc misrnarch o f lil'(; hist'Ory SF!':lll')',\, ",ill I I illlill)" l,r .~(, : ISllIlS or nl'hl'1' dim:!1 ie p:lr:IIIK'rCI'S (phcllology), 11_1 ,'\,11111,1,' , VlIll,'l'g illg ('1'11111 lIihnn:llillll I(Hll 'a d y ill I Ill' ,~ pl'illl!. , IlI'l i lll A 750 I, Role of Climate Change 187 500 250 1c 1000 1000~ l!l 'iii 750 750 500 c: 0 <U S Co n. 500 I .......... 250 250 0 0 100 200 300 Year 400 500 FiGURE Ii-4-, Overkill by the selective harvest of juveniles (less than 6 years old) of ,) simulated population of the extinct giant marsupial Diprotodol~ Ifptatum. Solid line is the total regional population (can)/i ng capacity = 1,000) and the (barely visible toward the bottom ofeach graph) dotted line is the annual number ofjuve niles killed by hunting (human population size = 150). (A) Constant hunting off lake. (B) Type II functional response (asslU11cS prey are na'ivc). (C) Type III func rional response (assumes adaptive prey and higher hunting pressnre), Source: I ~ rook and Johnson, 2006. snowmelt has exposed critical food resources (Parmesan, 2006; Bar 11osky, 2009). Although numerous examples of climatic change stimulating Changes in local abundance or geographic range changes exist, there are I ~' w examples ofclimate change causing worldwide extinction in tlle ab ,.I.'IKe of any other biotic stressor. Examples such as the golden toad /l/~li) perigle11.es) and harlequin frogs (genus AtelOp~H) may qualify ( 1',lrl11esan, 2006 ) for recent times, and in deeper time, the demise of Il'ish dl<.. (Megaloceras) in Ireland, and horses (Equus) and short-faced 11~' , lrs (Arct()du~' ) in Beringia seems artributable mainly to late Pleis I ilL CIllo' climate changes (lhrnosky, 1986; Gutllrie, 2003; Barnosky et tI ., 2()04 ; Koch ~lIld Bamosky, 20(6). Although available models fail to ,I,f"qll:lld y simllble Il)cg:1 t:JlIll:11I.'xt"incrions based on climate change ,tI, 1\ Il' ( Hre )()k :lIld Hll\ov111:111 , ,2.00·1,; I.Y()IlS 1..'1' :11. , 2004:1), model ing <thd IHH Quatern ary Extinctions and Their Link to Climate Change EVIDENCE FROM THE PAST "Il)pirical evidence has shown climate change alone to cause extinctions t(species ranges are restricted by barriers that prevent them from mov ill g' to track their needed climate space (Barnosky, 1986,2009; Thomas : 1 ;\1., 2004). It is precisely this latter situation in which the world's 1:11111;\ (and flora ) today find themselves. 'I'he late Quaternary was a period of major natural climate change (Iig. Il-5). The most prominent events were the glacial-interglacial cy < ks, which have repeated thirty-nine times over the last 1.8 million y,·.lrs; the last nine cycles show about a 100,000-year periodicity. Dur iIlg Iltese shifts in climate, the globally averaged temperature changed hy 4 6 degrees Celsius-comparable in magnitude to but at a much ·,1, IIV~T rate than that predicted for the coming century due to anthro II( ') 'SII ic g-Iobal warming under the fossil fuel-intensive , business-as 11 ' .11.11 .~rl'l w·io (AIFI; http: //www.ipcc.ch:IPCC.2007).Triggered by <l1 'l> il.l1 Ie )rcing and reinforced by albedo changes (ice-sheet retreat or ) ',1 i 'wilt ) ,IS well as the feedback of terrestrial and oceanic greenhouse 9 7 1/i ,/cII MIU) 4 ~ 11 l :j NIl.';;' o ~ 'i : . Tv Tv, '. TVII " \~ "" , . ~, ; ! - - - ":;",.'. - .~.:. - ,.; ; lJ 100 200 300 400 Age (kyr BP) ,1',/, .v~, " !, ~ !d.',I '1J'1' ~:' \<~/ ~ '1.Ii'1 ··· ·u :- - , . 11111 T~X TvII , - 1? t, '- I 500 600 700 000 ill( i IIltl l, II 5. /\lltarctic icc corc record of polar temperature (top; dClitcriulll d,il ,I) ,11,,1 ( ,1I'h, III Ii il ,xide.: rOllcclltr;lI'ion (bortoll1 ) for the.: pas!' 800,000 ye.:a rs. I I, wi'I' Ii, I,d lillnl show m t;;11l I'C1l1pel'ature.: and c~rholl dioxide.: v;llll e.~ ove.:r dif'l\;I\:llt ilill I ",110" M,ll'in<.' isot'opc SI : I~CS arc in il':lli<.:.'> :111(1 !\b ~'i: III ~'l'Il lill : l t i () Il ~; by'l'x (c' I'" , 'I,) ' 1'1,,' I'\' ll i" III>I.I<·k lillrs show till' lilllillg .,1' III\,!\,II:'IIIII.II (·,llilll.'li'"IS ill New '/ ,1,1 1." .. 1, NI II ill /\1I1l'I'i, .1 , ,11111 /\IISII',lIi .1 (k 'i 11'1 ;" ,111 ), S' 1111 '. ,': M. Idil i~·.1 1'1'11111 1,111111 , I .d" 'DOH , 189 gas release, the longer-term glacial cycles also were punctuated by nu merous short-lived (and likely regional-scale) abrupt climatic changes, such as the Younger Dryas, Dansgaard-Oeschger, and Heinrich climate events (Overpeck et al., 2003). These short-term, high-magnitude cli matic changes probably exacerbated any stresses that the larger-scale glacial-interglacial shifts were placing on species, although all of these kinds of cyclical cbanges seem within bounds of what species have evolved to withstand in the absence of impermeable geographic barri ers (Barnosky, 2001 ; Barnosky et al., 2003; Benton, 2009). Mechanistically, climate change over the last 100,000 years changed vegetation substantially in many parts of the world, although rhe naUlre and magnitude of the changes were different in different places (Barnosky et al., 2004). In central North America, for example, rhe end-Pleistocene witnessed a relatively rapid transition of vegeta 1io nal struculre and composition from a heterogeneous mosaic to a 1I10re mnal pattern that was relatively less suitable to large herbivores (G raham and Lundelius, 1984; Guthrie, 1984). Abrupt events such as 'he Younger Dryas probably superimposed even more rapid vegeta I ion shifts (Sulart et al., 2004). In Australia, the climate became more .trid as the depth of an ice age was approached, and the surface water .Ivailable to large animals would have become scarcer and more patch~ il y distributed (Wroe and Field, 2006), Yet, most megafauna species ,IJlpear to have persisted across multiple glacial-interglacial transitions, ' lill y to become extinct within a few thousand years of, and in some ' , I.~es, coincident with, the most recent one (fig. 11-5; extinctions 1II.Irked with black vertical bars). 'I 'he resilience of species can be inferred from the fossil record and 1111 )k;cular markers (Lovejoy and Hannah, 2005). In the Northern I k misphere, populations shifted ranges southward as the Fennoscan .1 1. 111 :u Ki Laurentide ice sheets advanced (or persisted in locally equa Ioli ' n.Jugia ; Hewitt, 1999), and then reinvaded northern realms dur !1I1', illterglacials. Some species may have also persisted in locally 1,II'ilr:lhle rdllgia that were otherwise isolated within the ntndra and il ,' /I Irewn landscapes (Hewitt, 1999). In Australia, large-bodied i', 1.111 I111:1 Is were able to persist throughout the Quaternary (Prideaux et II I -t o() 7 h), even in remarkably arid landscapes such as the Nullarbor l'l.dll ( I'ridc:wx ~t :11., 2007:\ ). ' 1'lll'I'C w<:n; nun y lilll l.o's durillg I'IH: h~r 100,000 years when the I 11.111,111 ' ''''P:II'<'lIll y ,~ 11 iii ,." rrl 'Ill ,', II II 1i,'YIi' w;\rm · w~r conditions, and li d' I~ ,1)'" lill (Ii !" , I I ,(I , 1>\ 1.~ l'd 1111 III" C"("' lIl.lIld il'l' l'orC d :l l':l), :1 point ~. 1')0 Quaternary Extinctions and Their Link to Climate Change EVIDENCE FROM THE PAST Calcium concentration (ppb) Range of dated extinctions 0 400 8?0 ing (in comparison to previous glacial-interglacial transitions) at that time negatively affect such a wide range of species and habitats (Bur ney and Flannery, 2005; Johnson, 2005) to the extent that once abundant, ecologically dominant animals simply disappeared? The an swer to this question probably lies in threat synergies. 12?0 o Madagascar, N.Z and Hawaii West Indies and Mediterranean North America 191 I I I 20 Eurasia Australia Threat Synergies, Past and Present I 40 80 100 Thousands of years before present 1: 11 illIW II Ct . till ' I.WI d\'1Io'il'1' G rc;c.: nland ice core calcium concentrations (parts per billion) O Wl ' 100,000 yc.:a rs. Low values indicate wet-warm conditions with relativc.:l y vL' ~l,; rarivL: (ovc.:r, and high values point to a cool-dry climate with spars\'! 1,.1, ,h,d w!,l:l'arion. Also marked are the last glacial maximum, YOlmger Dry:\" ,iI '11'I il , 'III lling c.:vc.:nt, and the Holocene warm period. The timing of extincriuw, • 'II i',l.l1ld ,~ II' t1I N :\1ld (OlltinUlts is indicated; also shown are the earliest and latest cxtilll III Ik rillg ia with Eurasia. Source: Burney and Flannery, 2005. i'( 'illl<>n.:cd by Ilew stable isotope data from Australia, as described ill 1\1'1)Ilk \.:1' :,1. (2007) ;)nd summaries presented in recent reviews (lbl III I ,~ky l' l :d., 2004; Koch <lnd Barnosky, 2006). Although such challg..., 1I11111111hrl.'dl y ltd to the disappear~l11ce of various species in local ;11\'.1 ', ,111.1 ,1 lrrrn l r1H.'ir abllllllalH.:e whcre th ey rcmained 0 11 the hnd~c1 1l(' , II \,V(' I'lllv1 n,s riley persisted regionall y or gloh~lI y lJnrii I'hc,; die-Ilil o I 1IIIIIn\ ·d ill r1h' 1:1SI li:w rens of" J)lilll'lllli:l 01' 1'1ll' Plcisl()(t; nc :1I1d illill 1111' I hllll\('IIl·. II' dilll,ll(' d l:1I1!\(' WI'I',' .1 dl'i vl'I' III' Ihost' t"Xlim'lillllll , 1\' 11.11 '11,1": ,'l1 lllill;'I'I'11I .1 .': 111111.11<1' rill' , 1 1'1'"I1I1/',I\, 11'l1l1l.d !',lllh.1I \\1.11111 The Pleistocene megafauna I die-offs provide a salutary lesson about the future of biodiversity under projected global warming scenarios, Over most of the last 2 miilion years, there was a lack ofwidespread ex tinctions, particularly of plants (Willis et ai., 2004), despite regular bouts of extreme climatic fluctuations (fig. 11-5). So what made the last glacial cycle different? We believe it was the synergy of mutually re inforcing events brought by the double blow of anthropogenic threats and natural climate change. Together, these produced a demographic ecological pressure of sufficient force and persistence to eliminate a ~izeable proportion of the world's megafauna species (Barnoslcy et al., 2004; Brook, 2008; Barnosky, 2009; Blois and Hadly, 2009)-a group whose evolved life-histo.ry strategy left them particularly vulner able to chronic mortality stress from a novel predator and modifier of habitats (Brook and Bowman, 2005). Without humans on the scene, dimate change would not have been enough. A good example of this interaction, using a method of coupling hioclimate envelopes and demographic modeling in woolly mammoth Nogues-Bravo et al., 2008), shows how the human-climate synergy pmbably operated in the High Arctic. The model indicates that mam Illoths survived multiple Pleistocene climatic shifts by condensing II H.:ir geographic range to suitable climate space during climatically un 1:lvorable times. Finally, however, the new presence of modern hu11I.IIlS during the late-Pleistocene and Holocene, at the same time as a liJll:1tically triggered retraction of steppe-tundra reduced maximally I\d l;l blc habitat by some 90 percent (fig. 11-7), resulted in extinction. '1'11<: important message is that mammoth populations' resilience was \\,\·:1k.em:d by habitat loss and fragmentation, as it may weil have been II I pl'\.:violis inrcrgl;1Cia is, bur during that last range reduction the 1Il,lIl1ll1ol'hs wen: 1111;lhk III CI>PI' hl'CllISc,; ol"rhe addition of predatory 1111 ..... .111\ . (and po,~si hl y IIlhl'I' 1.1I111.~\': I!l(' Illodifications) by human 11!11!11·1'11 . t, i 11)2 EVIDENCE FROM THE PAST Quaternary Extinctions and Their Link to Climate Change 193 ing a similar collision of human impacts and climatic changes that caused so many large animal extinctions toward the end of the Pleis tocene. But today, given the greater magnitude of both climate change and other human pressures, the show promises to be a wide-screen, technicolor version of the (by comparison) black-and-white letterbox drama that played out the first time arotmd. Conclusions I:11 111111 II '7, (:1im:lI'(; l:I1velope model of habitat suitability in Eurasia for woolly 111 ,11111111 'I'll (M I11NNU/,tfJUS primigenius) at five times over the last interglacial-glacial 1I11 1'I'!', I... i.t! Ly.:k:. (hrk.(;\' shading indicates higher suitability. Full glacial condi I ill ll l, 111\ I I1'J'l'l I :11' 2 1,000 years before present (kyr BP), warm conditions (as warm "I ' W,l l'lm'\' 1'11 :111 I'()day) at 126 and 6 kyr BP. The white lines indicate hlcely north 1'1'11 lin Iii .. I' J1(;l)pk:. Line is dotted where there is uncertainty about the limit 01' 11111.1('1'11 IHIIH;l1lS, Source: Nogues-Bravo et al., 2008. III prin cip le, the same sort of fatal synergy is now attacking many ,-:pl'l'ics, bu t in a much magnified way. Modern climate change is oc I IIITiII!!. ~I t a ml1ch faster rate than past events (Barnoslcy et al., 2003) ,II id hCP.~111 in ;) world that was already relatively hot because warming. ,'; l.Irl'nl ill :111 interglacial ratller than in a glacial. By 2050, the planet is l'I'"jrl'I'l:d ro be hotter than it has been at any time since hum ans I'l' l li ved ~lS a spec ies. And the backdrop of human pressures on whi<.:h tid,,, r Xll'e11l..: dimate change is taking place is more pronounced thall I'WI' hdhr..:; in rhe twenty-first century the human enterprise reacil<.: s illll) :-tli W 1'1le rs or rile planet (Brook et aI., 2008). Not only arc \oW ":111 1> 111).:, d1c d im;l !'e irsdfro change (Miller ct aI., 2(05), but thanks I'() IHII' :tll'<":lll y hi /}. h popul:1rioll tknsi ry ;1I1d ongoin g popu lati on g rowl'll (III',. II .~) , l'Xlv11sivv :lppropri :ll'i()11 nrn:HIII':tI ('; lpir:11 , :H1d recl1llolugi l.tI I' XI'.IIISil \l1 (,"i ld1 l'll ('1 :tI., 2()()7), WI ' :II'('l illli li11)" m()l'L' I'h :1I1 L'VCI' 1)(' lllil ' 1)llIn' : : pl'~' il" ';' :ll1ilil )' iii Ir.I \'k 1111 '11 111 'I'1"'tI lI,d)II.II :' :IS dim,lll ' I'III", 1''1,illl V :i ll III .11 II ,,.:n II II' ('0 11 111" 1'11 11 f 01' III :11 II 'I I , w( ' ,11'\' \V i 111\ ,,'i:, I , The important message from the late Quaternary megafalmal extinc tions is not so much that humans caused extinctions in many (maybe most) places and climate caused them in others. Rather, the key point is that where direct human impacts and rapid climate change coincide, fatalities are higher and faster than where either factor operates alone. It is the synergy that presents the biggest problem, and that synergy is exactly what we find ourselves in the middle of today. Indeed, syner gies between seemingly different causal mechanisms seem to charac terize mass extinctions in general (Barnoslcy et al., 2011). Today, that intelligent predatory ape, tlle human species, is driving a planetwide loss and fragmentation of habitats, overexploitation of populations, deliberate and accidental introduction of alien species be yond their native ranges, release of chemical pollution, and tlle global disruption of the climate system. Most damaging of all is tlle interac tions among tllese different threats, which mutually reinforce each in dividual impact. Are the modern extinctions resulting from these pro cesses a much magnified version of what already happened once to canse the late Quaternary megafauna extinctions, and can this perspec I·ivc illuminate how to chart the future to avoid an even more severe hiotic collapse? The emerging consensus quite clearly says yes, and Ihat conclusion, in turn, implies that only a systems-based approach to til reat abatement will be effective in staving off future extinctions. Conversely, coming at the problem from trying to figure out what v:llIscd Quaternary extinctions, the question "Was it humans or natu 1,11 ,'I i111 ate change that t(xever ended the evolutionary journey ofhtm drcds of mcgabllnal species?" is the wrong one to ask. That question i1 111 ic ip ~ltcs ;) uni cau ,d IllCch:lIJisrn, which might be appealing on parsi illOllioliS gT() 1I11d,~ , hIli ,':111Iltll h<.: ,~lIpported by fossil, archeological, l i lll : ll()l()g i~·: tI , :l1ltlllltllldill)" ('vi dclI l·(' . IllSI' ~lS I()r our modern global Il;'Hliv('rsil y ' I'i ,,:i,", 1,111' i.lill'l (1" 1'" , ()VI'1'IlIJllring) mil)' dotl1i 11 ,111 ' III 1'111' II!.\( I' , ,111.1 ,I /11 '11111.11.111111 :,111111 '\\11,,'1 '1' d,-:\, (1',1'" , .1 ,~ p(·, ' i\' ,'·: I 1')4 Quaternary Extinctions and Their Link to Climate Change EVIDENCE FROM THE PAST disappearing off a mountaintop that heats up too much). But at the global scale, synergy among the distinct proximate causes adds up to IIlOI"C than the sum of each individual cause. If one insists on a mini malistic answer for what caused the late Quaternary extinctions, it seems to be this: the actions of colonizing and expanding prehistoric hllmans (primarily hunting and habitat modification) seems omni pn.:scnt in the past global extinction (Brook et aI., 2007; Gillespie, OOH), but in many cases, species were left much more vulnerable be (:lllSC of climate-induced range contractions and changes in habitat (JI':llity (Guthrie, 2006; Nogues-Bravo et al., 2008). The degree to which climate change was the "straw that broke the ~ .lInd's back" probably differed to some extent for each species of ex r iIll:t Quaternary megafauna, and will only be really understood after (ktailed study of each extinct species (Koch and Barnosky, 2006). But Ille bet that even "natural" climate change synergistically exacerbated t.:Xtinctions when human pressures first increased is worrisome in the i11( )dcrn context. The climate change is now far outside the bounds of whar is normal for ecosystems (Barnosky, 2009), and the other kinds ()j" 11lIman pressures on species are so much greater than Earth has ever seen. In the end, it will not only be the extent to which we can mini Illize each individual cause of extinction-increasing human popula ri( >11 and attendant resource use, habitat fragmentation, invasive spc ('il:s, and now, global warming-but also the degree to which we call Illinimizc the synergy between each separate cause that will determine jllSt how many species we lose. Aclmowledgments \lVt.: thank Marc Carrasco, Kaitlin Maguire, Lee Hannal1, and t'I'V( I lymolls reviewers for constructive comments. BWB's research (Ill ('his topic was supported by Australian Research Council gr:lIli I )I'OXX 1764, :)lld ADB's by grant DEB-OS43641 from the US N:l i ;( III :d S<.:icllcc foundation. . 1I1<)! REFEREN C I';S I\I, '''Y, J. l OIlI . 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MOSBLECH '': 1 , We have found no examples of global plant extinctions from the trop ics within the Quaternary, Examples ofextinctions over longer periods of time are readily documented within the fossil record, with the loss of whole families evident between Eocene and modern times (Morley, 2000, 2007). Herein lies a clue to the problem of detecting extinction of tropical plants-the ta.,'(onomic resolution of the fossil record. Most of the paleobotanical records that we have from the tropics are based on fossil pollen, plus a few on wood, and even less on seeds ,1l1d other macrofossils. With a few exceptions, fossil pollen identiflCa tions are at the genus or family level, and so an extinction sufficient to remove an entire genus would be the minimum detectable level of loss. Because many tropical genera contain congeners that occupy very diHerent habitats, losing all of them requires a huge change in the eco sy~tem, or a lot of bad luck. Over long enough periods of time, evolu I iOIl, luck, and continental-scale modifications of climate are possi Ilk, and extinction does become evident. Because of this taxonomic I)i ::l.~, we actually have a clearer vision of extinction that took place be I w\.:cn rhe Eoccn( ;lI1d rhe M ioccilc than we do across the much ,II Ie )In: !' rill1csc lic e)f 1'11(' (J II ; lr~TI 1:11')'. We can sec at that scale that major i lilll:llic ( Will'S :1t1d SI't'\':ld "i' lin' inil i:l rcd cycles of species loss and 'IP"i ' i :llil)tl , II i s 111)1 1I111'1',I!a)ll.lhk '" S IIPpCl.~~' rhar the spread of fire II)"