Saving a About Island Press 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 world, 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.
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Wlr~/lil(I//{J1I1( :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 111'11years of severe 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 llil'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 1IIlIv il ri1wrizing, modeling, and digging (for their fossils or environ
111,'111:11proxie s) 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;
~JI ' I 'III\ ;,~- lklVOet ,)1., 2010; Price et al., 2011). III Ihis dl:lpt<:r, we t(>ClI S on recent work that explicitly considers il l!' I'~'LIIive ruk of !'larur:)1 climate change compared to nonclimate
111111 1.111c :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' hegin with a short
I' \ I' IV c ,i' I hI' )',Iuh,d p.IIII'I'1i I)t' (~II:II'l'rl1,1ry l'X I'in~ '1iOlls 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 Quaternary Extinctions and Their Link to Climate Change 181
vldnt:rable to direct human impacts and climate change. We then ex
IIIII'L' -40kyr 13.5kyr I how the pattern of megafaunal extinction corresponds to borh ~1>'/\ 4' 2' 1 1 2 ~3P/\ 15 \I' II chronology of human expansion and climate change and their pro ~~--:-i"~~~]17· 11.5 11\5. 3 ISO.13f lcyr I~i=11.C~1Holocene /('\ 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,IC lioIlS, it exacerbated overall extinction risk tremendously. Thl' 1.11l( ' IIIIIIIC message is that the synergy of fast climate change wil'h
III' 'I I' dirclT human impacts can have particularly fatal consequencl'~ ~<~:rJ '3' ' . \ ',ll III.III,V Iionhuman species-and this is particularly true today, wh~'1l
j~loceneI ,.0i!~. 1111111.111 ildhl L'IlCeS, including climate disruption, are so dramaticallv ~J II 11"1111 111 ,', , . I'hcy have ever been in the past. ~ '
6 t/ / -r >16 I ~Okyr II 51'~O 1? I'~xtincri on and Vulnerability ofMegafalma ~72.44k--II 4q .28 I..... __ ------'yr I 1'111'"lid () II.III.:nLlry (late Pleistocene and Holocene) die-offs COI11
I" 1,',('..1,I :,i}'.lIi1i~':1I11" global mass extinction event, which led to the eli III fi nu608 of extinction Relative size of extinctCorrelations in time Numbers indicate how 111, 1111111 ,II h.dt' lit' :111mammal species heavier than 44 kilograms (100 taxon icon corresponds -, many genera have robust Moslly Human to relative magnitude of L oJ Humans arrive dating control evidence I" 1111,,1:,) ,llleI 1I1'II~Tbr g<.:-bodied fauna across most continents (Au., extinction. Number of Moslly Climale • Climatic change except as indicated: extinct genera is listed Provisional evidence I, ,lii,l , I':"":I.,i: l, Norl"ll alJd South America) and large islands (West III InsuHicient data on each icon. ? Needs more work cI11',', , M,ld,I).!,:ISI\lr, alld N<.:wZea land), between 50,000 and 600 ye:ll" 11 1"" ,1' 1"\"'("111(Koc h and Barnosky, 2006). The losses included large I I ' Ie 11(/, JT-I. Late Quaternary megafaunal extinctions, human hWlting, and di 111.1111111:11., (L·.g., mammoth, genus Mammuthus), reptiles (e.g., gialll lilollt' ( /lange on the continents. The dashed box indicates the credible bounds of
~; a l' I"lIeI:, lIdl:1., MCJl /t,lnia), and huge flightless birds (e.g., New / ,(',1 IIi, IIrsI' arrival of modern people, Homo sapiens sapiens, with the best estimate ad 1.11111111'1 :1 :lIId Ausrralian Genyomis). In Australia, around fifty spccic.\, i'" , 'III In the human figure (the latest estimate for Australia is about 48,000 years lilt Ilid i1I,l!, rli inoc eros-size wombats, Short-faced kangaroos, and pr<.:d,1 III" Ikyr BP]). Substantial climate change events, predominantly the last glacial I, 'I I' I" I.'ISIII IlS disapp<.:ared (MacPhee, 1999). In North America, 1'111 Iii 1\ il I IlIlI1 ,lnd Holocene warming, are indicated by gray shading inside boxes. ell"llll Inll was SOI11<.:sixty species of large mammals plus the laq.!,('hl " !III' (' : K.och and Barnosky, 2006. l, il'e1:: ,lIld !"orroiscs, and South America saw the disappearance o( .11
1('.1',1,~ixly·six Iarg<': -Jl)<1111maJspecies. Eurasia and Mrica were less 1I.1le! 1'11),/ ), hut plausibly include: (i) being outcompeted by newly evolved Ii ii, 1'"1 III,'Vl'l'I'hc!t.:ss saw major losses in their large-mammal faulI:! , Id II I Illv;tsive spccies; (ii) failing to adapt to long-term environmental " "'11, lIld 8<.:vcmet;n specics, respectively. Region by region, these n , I 101II } ',l' (e .g. , climatic shifts); and (iii) reduction in abundance caused 1i,It linll I,'VCllrS f()lIowni within a few centuries to a few millenlli:1 IIIi 11\ 1,IIIdpm disturbance events (e.g., epidemics, severe storms) with a 11"11 1 di8pL'rS:11 1-l00'YUlsapiens to new lands, and wne parricularly :W or IIi "wl/lIl"m bilur<.: to recover to a viable population (Blois and Hadly, 1'1'1( ' IVhl'lI I ht;y Were also <.:l1twined with changes in rhc n.:gioll:" ')I '( 1)')), !\ C()llJlllOllly cited g<':llcralization is that larger-bodied verte 1,.II,b :II l'Iill1:lI~'SY.'I~l'lJl(fig. II - I ). 1".111" , (w il'll I'he L'xtrctne rccwr t()rm being the Quaternary mega SCIIV".II W.IS Ihl' 1..':11 IS:" IIlCCh:lIIisll1 hdlind dll's(" eXIilll'l inns \ I, 11111101) .11' 1' 11101'1.' eXt'illCrio/1-prone I'h;lIl smaller bodied ones (Bodmer 111"1,,, 1111111:111.'" Ill' hlll'h? The drivers 11f'I,il"il ('xlililliIIIlS, P:I:;I ,lilt! I I ,iI , 1')')7: McKi'lIH'Y, II)()?). I\n ':IlISl' hody sizc is inversely cor- l'I" ~t'lll .,Ill ' 'lfi "11 '~lIq1J'i.':ill!,,Iydin illill I" I,ill '.I"IVII (Nit I\i llll\ 1'. I I,'oj I'd Willi 1'"1,"1.11i,,, I ",iI,\" 1.11'/',1' h, It lit'd .lIlirn:lls rL'nd ro h<: kss 11\1 EVIDENCE FROM THE PAST Quaternary Extinctions and Their Link to Climate Change 183
.11IIIlld :1I1r and so more intrinsically vulnerable to rapid change and de hunted by invading prehistoric people in Pleistocene Australia, arbo Illographic disruption. Indeed, when armed with some knowledge of real (tree-dwelling) species occupying closed forests suffered far fewer ('llIpiridly well established biological scaling rules (allometry; Da extinctions than saVaru1a (grassland) species, and of the latter group, 111111h, 1981), such a hypothesis makes a lot of sense. Large-bodied an tbose with high per capita population replacement rates (e.g., grey III 1.1 Is such as elephants or whales produce only a few, precocious off kangaroos; Macropusgiganteus) or the ability to escape to refuges such 1'1'I'illg , but invest substantial resources into their care. This life-history as burrows (e.g., wombats; Vombatus ursinus) were best able to persist :;II.IIl'!'\Y kads to the death of juveniles being a major demographic set (Johnson, 2005). I•.Ide ()II a population-wide basis, even an apparently small additional 1.-,,1'10" chronic mortality can result in rapid declines in abundance .llld, within a few centuries, a collapse to extinction (Brook and John The Role of Human Arrivals :.(111, 2()()6; Nogues-Bravo et al., 2008). The extinction proneness of I.II,}"Cbodied animals is further enhanced because of other correlated During the last 100,000 years, modern humans have spread across the
11. lil s such as their requirement oflarge foraging area, greater food in world from their center of origin in Africa, reaching the Middle East 1.1"(" high habitat specificity, and lower reproductive rates (West and by 90,000 years ago, Australia by 48,000 years ago (based on tlle most
I~i'( 'WII, 2(05). s(:cure evidence presently known , Gillespie et al., 2006), Europe by Why thcn (in evolutionary terms) be big? Three reasons are that 40,000-50,000 years ago, SoutllAmerica by 14,600 years ago, NOrtll
I.II'~\('~\llil11alsarc long-lived (so have multiple attempts at reproduc America by 13,000 years ago, most of the Pacific Islands by 2,000
Iic'11) , have relatively better heat regulation and water retention than lears ago, and New Zealand by 800 years ago. (For dates estimated by ';111.111.lI1inJais, cmd have lower predation rates, especially when herd radiocarbon dating, the radiocarbon age is calibrated to calendar III)',. Their size protects them from all but the biggest predators, thcy I(: 11.11It':1 great capacity to ride out hard times by drawing on their fat re hy climate change: a wet penultimate interglacial probably encouraged ·.C·I \Irs, rhc)' can migrate long distances to find water or forage, and 111(: spread of early Homo sapiens out of Africa, and in the Northern t1lC'y L'all ()pt not to reproduce in times when environmental condi Ilcmisphere , end-Pleistocene immigration into tlle Americas was fa II. 'IIS .IIT unt:1vorablc, such as during a drought (Brook et al., 2007). ,ilirated by glacial ice sequestering water and lowering sea levels, I'IIIIS ill I'he majority of circumstances, being big is good, because il which in turn exposed a land bridge between Eurasia and North .ICI ~.I S .1 demo graphic buffer. Indeed, such ecological specializatioll \ l1lerica and opened coastal migration routes. At the very end of tlle I. '11iIs Ic. evolvc repeatedly because, in relatively stable environments , I'kistocene, it was global warming that melted ice and opened an ice '~I'1 ' 1 I.llisl species tend to be better than generalists at particular narrow II'n : CI)rridor through central Canada for a wave of Clovis hlUlters. 1.1.·.k::. Ilmvev t:r, when an envirorunent is altered abruptly at a rail' A striking feature of the megafaW1al extinctions is tllat, in every ma .11II ."" lie )l'In:11b :Kkgrollnd change, speciallst species with narrow cco l' '1' Illstance where adequate data exist, the extinction follows the first I. 'I',Ic .11j\l'l'It:n .:nl:cs bear the brunt of progressively wlfavorable contli Ill'i v:d of people on a "virgin" continent or large island within a few II, "I S Slll'h as habitat loss, degradation, and invasive competitors (ll 111111l11'(:dto a few thousand years (fig. 11-1). This point is further un I 'II" 1.11III' S ( B:lllllf'(lrd, 1996; Harcourt et al., 2002). An extremc CVC:III, 1I"I':K'(lred in figure 11-2, which shows the short overlap period for well 'III, It :I.~ : 1 holide strike tt'OI1l space (Haynes, 2008) or an inrclligC:III, 1,I1(',llllc!4aflllnal remains and archeological artifacts, in New Zealand, "" "'1" l1l, w Ic:lding bipedal ape (Mart in, 200:;), tbar also widely allrl" r~I'1111 America, and Australia, based on the latest dating and sample se 1.IIIoI",,·:IPI:S by pracrices such ,IS burning and farming, can be rbc; k vc'l I, , Ii, III protocols (Gillespie, 2008). (Note the different time scales on 111.11IIIIIJill gl.·S Illl' upl"ill1ality ofrhi s r(:gu larly evolved srrat(:gy o/'l:lI l',c 11.111o ·I N1\ , B, and ( :- rh(:se three (:vents wcre not synchronous in time.) I"" Iy ..,i'I.I·. I 111111iden e\.· :donl' is nor sulri(iC:1l1 evidence for causation, but this con- 'I'IH' ,·ll viI'Clnllll·1I1.l1(,()III~'XI :lI11IIYP~·I)t'II\1'( ·.11,~c) IIdp .1Is di (' t.IIl' ,III I'" 1'111Y .11 I hI' vny k.I.~1 1)1'( )v il k s sl)'( 1I1g L'irCIln1Sr:111rialsupport for the III 1'..11 Ii .';) 11 \ I\"~I)IIIII;('Ic. dl.lll1\(· CII IIl)VI·1 I.II·C··.·,,'I ·. l:clI illl·:I.IIIlI" WIIl'II It" ,I 111.11.1 1111111.111pn':" '111(. \V.I.'; .1 lit·, '·S .~.II'Vpl'rc 'l )nd iI ion 1;)1': H.'(I.;lc:rar~·d IH4 EVIDENCE FROM THE PAST Quaternary Extinctions and Their Link to Climate Change 185 A,_ fauna, We are a species that broke a fundamental ecological rule: large ~ Rattus exulans = & rat-gnawed seeds -==== 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 Moaeggshell 1 nently displaced tl1e once-ablmdant biomass of megafauna, The point, New Zealand well illustrated in figure 11-3, is that when the species richness ofmega ~ooo 1500 1000 500 0 -500 -1000 -1500 -2000 -2500 fauna crashed to today's low levels, their equivalent total biomass was Calendar Age (years caiAO/BC) replaced by one species (Homo sapiens), Indeed, we surpassed the nor mal prehistoric levels of megafaunal biomass when tl1e Industrial Rev B ~ Clovis-age olution commenced, and now, when combined with our livestock, ~ Archaeology ~ vastly outweigh the biomass of mammal faunas of the deep past- an ex . Mammuthus Smilodon fatalis plosion of living tissue supported primarily by the use of fossil energy & Canis dirus i (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 North America ~ cies) demonstrated by tl1is Pleistocene history has a dear conservation 10 15 20 25 30 35 implication: to avoid losing many more species as the human popula Calendar Age (ka calBP) I'ion grows in tl1e very near future, it will be necessary to formulate poli c cies that recognize and guard against an inevitable energetic trade-offat the global scale, The pressing need is to consciously channel some mea ~ Archaeology - 1·e charcoal indirect OSL 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) Eurasia Australia Q. 400 Australia 14 (/) 1 Beringia 0 q' .--.. Americas III 350' - .... , 12 :'(1 30 35 40 45 50 55 60 65 70 75 80 85 90 c:: ... X :;:J 300 - c:: Calendar Age (ka) III 10 0 1ii Ol 250 8,0 :-§ Q) :;:J Q. 1I11 II1IU , 11- 2 , ::2 200 6,0 Dating data on human-megafauna overlap in New Zealand (A) , 0 150 oB ~It) t "~ 4,0 (L N III 'I h AnH.:rica (B), and Australia (C), The dates are stacked from youngest (t'ol') '0 It) ~ ~I ill 100 ~I'" 2,0 I,. ,.1.il-SI ( htIITom) for the archeology (dark shading) and oldest (top) to young<"" ..0 f" • E 50 0,0 (I" 'lit lIll ) li)/' Ihe animal remains or proxies (light gray shading), Bars rcprt'S"11i ::l Z ,jdtilll\ IIIh:crr:lillfies, SOl1l'ce: Gillespie, 2008 (includes detailed legend), 100,000 10,000 1,000 Years before Present 111('1\,11: 1111):11 l:Xrin <.:tioI1, l:spc<.:iaJly given the evidence that mo~to( 11II Il,t 1111(1 , 1/-3, Dcclinc in gloh:l1111l'gaEllma hiodiversity (number of species; light " XI illl ' l I.IX :I slirvi v<.:dthrough pn:vioLls, <.:qll:llly pronounced Cli vi 1'1 III 1\1,1\') l'l't.:r rh t.: i:l~rgI:Ki:ll -ill,.,:rgl:lci~1 c yrle, plottl'd against tbe increase in world 1/1\' 111.11 Ill'l'llIrh:II'ioll,~bd(lI'( ': hum:uls :uTivnl. i'''11111.11i(lll ,~i'l.t'(11'1/011-10 .l'11/,ir'll,I , 1\1\.11111'l'Xlill \:I'ioll evel1t~by (;t)ntincllt arc indi IiiII' oj' :c l'vidl'Il\ \ ' \'III1I\ '~1 1)111,l. ~,~rssill!-!- /\ f'llIlIwi' illdin l 11' jOlllllv '; , 11, '.1 I'y .I :II'k )',1':1)' ,II'I'IIW ::' ",I 1'111"10' 1.111.111 oi' Y" :II'S hdc Irc p/'l,~l'I'lI'),so\lrce: 1i1(' I',I"I>,1I l 'i N(' ill 1111111.111 :lhlllld,lIh '\' ,\lld 1111' 1'" ' \ 11'IIIIII ,':III ,'il' "I"III1 T ,,1 II'"II" lIkl', ./,OOH , I H(l E V IDE NeE FRO M THE PAS T Quaternary Extinctions and Their Link to Climate Change 187 1000 ,~elldy toward humans, for example, in the form of enhanced sustain A :Ihk farming practices and stepped-up efforts to protect and expand ex 750 iSI ing nature reserves. Also critical will be developing alternatives to 500 I,l,~sil fuels for the energy that currently sustains the global ecosystem, "~ IIL'cially humans, so far above its pre-anthropogenic level of mega 250 1.11111:1hiomass. Iluman impacts on late Quaternary enviromnents were many and \'.Iried (Barnosky et aI., 2004; Lyons et aI., 2004a). The role of prehis 1000 c I'll'i( pcople as hunters of big and small game has been reviewed ex 1 1000~ 750 Il'Ilsi vdy (Martin, 2005; Surovell et al., 2005; Grayson, 2007); meat l!l 750 IV.IS 'iii 500 (learly a component of the hunter -gatllerer lifestyle (Bulte et al., c: 0 500 '()()(l), blll killing may have also occurred for reasons beyond subsis 1.11II I~I ,Ipl' Sl':lk (and in doing so, perhaps radically altering local di Year III,I!!': Milln ct :Ji., 2005) and by introducing commensal species such FiGURE Ii-4-, Overkill by the selective harvest of juveniles (less than 6 years old) of pi" 0111 )', ," (I:inkl, 2005) , rats (Duncan et al., 2002), and disease (Lyons ,) simulated population of the extinct giant marsupial Diprotodol~Ifptatum. Solid C', ,II ,, W()/I,h). Ovcrkill, the hunting of a species at a level sufficient to line is the total regional population (can)/i ng capacity = 1,000) and the (barely ,It iV(' il 1'1 ill(\ ion, with or without an additional pressure from fac nl visible toward the bottom of each graph) dotted line is the annual number ofjuve Ie1\", ,'''H' I! ,IS hahirar modification and clin1ate change, has been shown niles killed by hunting (human population size = 150). (A) Constant hunting off \1,111'.1 vi,lhle killing mcchanism for megafawlal species (fig. 11-4) if' lake. (B) Type II functional response (asslU11cSprey are na'ivc). (C) Type III func II H' 1111111CI'S :t1so could LIseother species when they deplete the original rional response (assumes adaptive prey and higher hunting pressnre), Source: 1.11,)',1'1 speci<.:s viable ablmdances al., Alroy, Ixlow (Bodmer et 1997; I~rookand Johnson, 2006. I()O I, Bruok and Johnson, 2006 ). snowmelt has exposed critical food resources (Parmesan, 2006; Bar Role of Climate Change 11osky, 2009). Although numerous examples of climatic change stimulating Nidlc' Illodding indicates strong correlation between specific climale Changes in local abundance or geographic range changes exist, there are V;II' i.lhk·s and spccies distributions (Hijmans and Grallam, 200(): I~'wexamples of climate change causing worldwide extinction in tlle ab NeI ) ',III'S Bra.vo ct ai. , 2008 ), and it now seems clear that climate i,~ ,I ,.I.'IKe of any other biotic stressor. Examples such as the golden toad k('y drlCrtllill~lIlrof whether or not a species can exist in a given 10Clk , /l/~li)perigle11.es) and harlequin frogs (genus AtelOp~H)may qualify 111.':1 likl.: hUll1an imp:1cts, climatic impacts on species are direct and ill (1',lrl11esan, 2006 ) for recent times, and in deeper time, the demise of tlil ~'I.I,Direcr impacrs incilide exccedin~physiologically imposed rnll Il'ish dl<..(Megaloceras) in Ireland, and horses (Equus) and short-faced 1'1.'1',11111'<.' :t llli prn:ipirarioll limits on a species, such as criticalrc.:mpcl,1 11~',lrs (Arct()du~')in Beringia seems artributable mainly to late Pleis 1111'(' I I! r',,'sII 0 Ids li)r J1lllsk oxen o r pikas, whieh have limited heal'-lo!,,'1 I ilL CIllo' climate changes (lhrn osky, 1986; Gutllrie, 2003; Barnosky et ,Ihilil i('s, Il1Ilil'l':l'l' irnpa(t~incilid c misrnarch of lil'(; hist'Ory SF!':lll')',\, tI., 2()04 ; Koch ~lIldBamo sky, 20(6 ). Although available models fail to ",ill I I illlill)" l,r .~(,:ISllIlSor nl'hl'1' dim:!1 ie p:lr :IIIK'rCI' S (phcllology), 11_1 ,I,f"qll:lld y simllble Il)cg:1t:JlIll:11I.'xt"incrions based on climate change ,'\,11111,1,', VlIll,'l'gillg ('1'11111lIihnn :llillll I(Hll'a d y ill I Ill ' ,~pl'illl!.,IlI'l i lll ,tI, 1\ Il' ( Hre)()k :lIld Hll\ov111:111, ,2.00·1,; I.Y()IlS 1..'1':11. , 2004:1), model ing "Il)pirical evidence has shown climate change alone to cause extinctions gas release, the longer-term glacial cycles also were punctuated by nu t(species ranges are restricted by barriers that prevent them from mov merous short-lived (and likely regional-scale) abrupt climatic changes, illg' to track their needed climate space (Barnosky, 1986,2009; Thomas such as the Younger Dryas, Dansgaard-Oeschger, and Heinrich climate :1 ;\1., 2004). It is precisely this latter situation in which the world's events (Overpeck et al., 2003). These short-term, high-magnitude cli 1:11111;\ (and flora) today find themselves. matic changes probably exacerbated any stresses that the larger-scale 'I'he late Quaternary was a period of major natural climate change glacial-interglacial shifts were placing on species, although all of these (Iig. Il-5). The most prominent events were the glacial-interglacial cy kinds of cyclical cbanges seem within bounds of what species have < ks, which have repeated thirty-nine times over the last 1.8 million evolved to withstand in the absence of impermeable geographic barri y,·.lrs; the last nine cycles show about a 100,000 -year periodicity. Dur ers (Barnosky, 2001 ; Barnosky et al., 2003; Benton, 2009). iIlg Iltese shifts in climate, the globally averaged temperature changed Mechanistically, climate change over the last 100,000 years hy 4 6 degrees Celsius-comparable in magnitude to but at a much changed vegetation substantially in many parts of the world, although ·,1,IIV~T rate than that predicted for the coming century due to anthro rhe naUlre and magnitude of the changes were different in different II( ') 'SII ic g-Iobal warming under the fossil fuel-intensive, business-as places (Barnosky et al., 2004). In central North America, for example, 11 ' .11.11 .~rl'lw·io(AIFI; http://www.ipcc.ch:IPCC .2 007).Triggered by rhe end-Pleistocene witnessed a relatively rapid transition of vegeta ~ ',I.~es, coincident with, the most recent one (fig. 11-5; extinctions - 1? 1II.Irked with black vertical bars). vII : . Tv Tv, '. VII " X T T , T~ 'I 'he resilience of species can be inferred from the fossil record and , "\~ "" . ~ 1111)k;cular markers (Lovejoy and Hannah , 2005). In the Northern " " '. ~,;! ,1',/, ',I t, -- :; ,. -.~.:.- - .v~, !d. - :- -, !, '- '1J'1' I k misphere, populations shifted ranges southward as the Fennoscan ,.;; ~:'\<~/ ~'1.1 .11. 111 :u Ki Laurentide ice sheets advanced (or persisted in locally equa . ····u Ii' 11111 'i I Ioli' n.Jug ia; Hewitt, 1999), and then reinvaded northern realms dur !1I1', illterglacials. Some species may have also persisted in locally lJ 100 200 300 400 500 600 700 000 Age (kyr BP) 1,II'ilr:lhle rdllgia that were otherwise isolated within the ntndra and il ,' /II rewn landscapes (Hewitt, 1999). In Australia, large-bodied ill( i IIltl l, II 5. /\lltarctic icc corc record of polar temperature (top; dClitcriulll d,il ,I) i', 1.111I 111:1Is were able to persist throughout the Quaternary (Prideaux et ,11,,1( ,1I'h, IIIIi il ,xide.:rOllcclltr;lI'ion (bortoll1) for the.:pa s!' 800,000 ye.:ars. I I, wi'I' Ii, II I -to()7h), even in remarkably arid landscapes such as the Nullarbor I,d lillnl show m t;;11l I'C1l1pel'ature.:and c~rholldioxid e.:v; lllle.~ove.:r dif'l\;I\ :llt ilill I l'l.dll (I'ridc:wx ~t:11., 20 07:\ ). ",110"M,ll'in<.' is ot'opc SI:I~CS arc in il':lli<.:.'>:111(1 !\b ~'i:III~'l'Illill:lti()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'lll'I'C w<:n; nun y lillll.o'sdurill g I'IH: h~r100,000 years when the I 11 ,~11 II w;\rm· 1.".. 1, NI II ill /\1I1l'I'i, .1, ,11111/\IISII ',lIi.1 (k'i 11'1;" , 111), S' 1111'. ,': M. Idili~·.11'1'11111 1,111111 , I .111,111' ''''P:II'<'lIlly iii ,." rrl 'Ill ,', II 1i,'Y Ii' w~rco nditions, and .d" 'DOH , lid' I~, 1)'"lill (Ii !", I I ,(I , 1>\1.~ l'd1111 III" C"("'lIl.lIld il'l' l'orC d:ll':l), :1 point ~. 1')0 EVIDENCE FROM THE PAST Quaternary Extinctions and Their Link to Climate Change 191 t, i Calcium concentration (ppb) ing (in comparison to previous glacial-interglacial transitions) at that Range of dated extinctions 0 400 8?0 12?0 time negatively affect such a wide range of species and habitats (Bur o Madagascar, N.Z and Hawaii I ney and Flannery, 2005; Johnson, 2005) to the extent that once West Indies and Mediterranean I abundant, ecologically dominant animals simply disappeared? The an swer to this question probably lies in threat synergies. North America I 20 Eurasia Threat Synergies, Past and Present 40 The Pleistocene megafaunaI die-offs provide a salutary lesson about the future of biodiversity under projected global warming scenarios, Australia I 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 80 and natural climate change. Together, these produced a demographic ecological pressure of sufficient force and persistence to eliminate a ~izeableproportion of the world's megafauna species (Barnoslcy et al., 2004; Brook, 2008; Barnosky, 2009; Blois and Hadly, 2009)-a 100 group whose evolved life-histo.ry strategy left them particularly vulner able to chronic mortality stress from a novel predator and modifier Thousands of years before present of habitats (Brook and Bowman, 2005). Without humans on the scene, 1: 11 illIW II Ct. G rc;c.:nland ice core calcium concentrations (parts per billion) OWl ' dimate change would not have been enough. till ' I.WI 100,000 yc.:ars. Low values indicate wet-warm conditions with relativc.:ly A good example of this interaction, using a method of coupling d\'1Io'il'1'vL' ~l,;rarivL:(ovc.:r, and high values point to a cool-dry climate with spars\'! hioclimate envelopes and demographic modeling in woolly mammoth 1,.1,,h ,d w!,l:l'arion. Also marked are the last glacial maximum, YOlmger Dry:\" Nogues-Bravo et al., 2008), shows how the human-climate synergy ,iI '11'Iil , 'III lling c.:vc.:nt, and the Holocene warm period. The timing of extincriuw, pmbably operated in the High Arctic. The model indicates that mam • 'II i',l.l1ld,~:\1ld (OlltinUlts is indicated; also shown are the earliest and latest cxtilll Illoths survived multiple Pleistocene climatic shifts by condensing II' t1I N III Ik rillgia with Eurasia. Source: Burney and Flannery, 2005. IIH .:ir geographic range to suitable climate space during climatically un 1:lvorable times. Finally, however, the new presence of modern hu- i'('illl<>n.:cd by Ilew stable isotope data from Australia, as described ill 11I.IIlS during the late-Pleistocene and Holocene, at the same time as a 1\1'1)Ilk \.:1' :,1. (2007) ;)nd summaries presented in recent reviews (lbl liJll:1tically triggered retraction of steppe-tundra reduced maximally III I,~ky l'l :d., 2004; Koch 1I11111111hrl.'dly ltd to the disappear~l11ceof various species in local ;11\'.1 ', '1'11<: important message is that mammoth populations' resilience was ,111.1,1 lrrrn l r1H.'irabllllllalH .:e whcre they rcmained 0 11 the hnd~c11l(', \\,\·:1k.em:d by habitat loss and fragmentation, as it may weil have been II\,V('I'lllv1n,s riley persisted regionally or gloh~lIy lJnrii I'hc,; die-Ililo III pl'\.:violis inrcrgl;1Ciais , bur during that last range reduction the I 1IIIIIn\·d ill r1h' 1:1SIli :w rens of" J)lilll'lllli:l 01' 1'1ll' Plcisl()(t; nc :1I1d illill 1Il,lIl1ll1ol'hs wen: 1111;lhkIII CI>PI' hl'CllISc,;ol"rh e addition of predatory 1111' I hllll\('IIl·. II' dilll,ll(' d l:1I1!\(' WI'I',' .1 dl'i vl'I' III' Ihost' t"Xlim'lillllll, 1111...... 111\. (and po,~sihly IIlhl'I' 1.1I111.~\':I!l('Illodifi cations) by human 1\'11.11 '11,1 ": ,'l1lllill ;'I'I'11I.1 .': 111111.11<1' rill' ,,11'1'"I1I1/',I\, 11'l1l1l.d!',lllh.1I \\1.11111 11!11!11·1'11. 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 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 I:1111 1111II '7, (:1im:lI'(; l:I1velope model of habitat suitability in Eurasia for woolly gies between seemingly different causal mechanisms seem to charac 111,11111111 'I'll (M I11NNU/,tfJUS primigenius) at five times over the last interglacial-glacial terize mass extinctions in general (Barnoslcy et al., 2011). 1I111'I'!',I... i.t! Ly.:k:. (hrk.(;\' shading indicates higher suitability. Full glacial condi Today, that intelligent predatory ape, tlle human species, is driving I ill lll, 111\ II1'J'l'l I :11' 21,000 years before present (kyr BP), warm conditions (as warm a planetwide loss and fragmentation of habitats, overexploitation of "I ' W,ll' lm'\' 1'11:111 I'()day) at 126 and 6 kyr BP. The white lines indicate hlcely north populations, deliberate and accidental introduction of alien species be 1'1'11lin Iii ..I' J1(;l)pk:. Line is dotted where there is uncertainty about the limit 01' yond their native ranges, release of chemical pollution, and tlle global 11111.1('1'11IHIIH;l1lS, Source: Nogues-Bravo et al., 2008. disruption of the climate system. Most damaging of all is tlle interac tions among tllese different threats, which mutually reinforce each in III principle, the same sort of fatal synergy is now attacking many dividual impact. Are the modern extinctions resulting from these pro ,-:pl'l'ics, bu t in a much magnified way. Modern climate change is oc cesses a much magnified version of what already happened once to I IIITiII!!. ~It a ml1ch faster rate than past events (Barnoslcy et al., 2003) canse the late Quaternary megafauna extinctions, and can this perspec ,II id hCP.~111in ;) world that was already relatively hot because warming. I·ivc illuminate how to chart the future to avoid an even more severe ,';l.Irl'nl ill :111interglacial ratller than in a glacial. By 2050, the planet is hiotic collapse? The emerging consensus quite clearly says yes, and l'I'"jr l'I'l:d ro be hotter than it has been at any time since hum ans Ihat conclusion, in turn, implies that only a systems-based approach to I'l'lli ved ~lSa sp ecies. And the backdrop of human pressures on whi<.:h til reat abatement will be effective in staving off future extinctions. tid,,, r Xll'e11l..:dimate change is taking place is more pronounced thall Conversely, coming at the problem from trying to figure out what I'WI' hdhr..:; in rhe twenty-first century the human enterprise reacil<.:s v:llIscd Quaternary extinctions, the question "Was it humans or natu illll) :-tli W 1'1lers or rile planet (Brook et aI., 2008). Not only arc \oW 1,11,'I i111ate change that t(xever ended the evolutionary journey ofhtm ":1111>1 11).:,d1c d im;l!'e irsdfr o change (Miller ct aI., 2(05), but thanks I'() drcds of mcgabllnal species?" is the wrong one to ask. That question HII <": /}. ;1I1d I ' :tll' lll y hi h popul:1rioll tkn si ry ongoing popu lation g rowl'll i1111 ic ip~ltcs;) unicau,d IllCch:lIJisrn, which might be appealing on parsi I', .~), i()11 ';lpir:11 :H1 (II . II l'Xlv11sivv :lppropri:ll' nrn :HIII':tI ( , d recl1llolugi illOllioliS gT()1I11d,~,hIli ,':111Iltll h<.:,~lIpport edby fossil, archeological, II \l1 1I1 li : : il (,"i ('1 WI li11)" L'VCI' · l.tI I'XI'.IIIS ld1l'll :tI., 2()()7), ' : '('l illli m()l'L' I'h: 1)(' I lllll()l() gi~tI,:l1ltlllltllldill)" ('vi dclIl·('. IllSI' ~lSI()r our modern global lllil' 1)llIn' ::pl'~ 'il"';': ll1ilil )' iii Ir.I\'k 1111'11 111'I'1"'tI lI,d)II.II :' :IS dim,lll' Il;'Hliv('rsily ' I'i,,:i,", 1,111' i.lill'l (1"1'", ()VI'1'IlIJllring) mil)' dotl1i 11 ,.:n '011 111" '1111 01' I , 11II ,11 \V ,, 111\i:, , ,'· I'III", 1''1,illl V :ill III . II , II II' ( 1 f III : 'I I, w( ' '\' i ' 11,111' III 1'111' II!.\( I' , ,111.1,I /11'11111.11.111111:,111111 '\\11,,'1'1' d,-:\, (1',1'", .1 ~p(·,'i\': 1')4 EVIDENCE FROM THE PAST Quaternary Extinctions and Their Link to Climate Change 195 disappearing off a mountaintop that heats up too much). But at the past selection pressures for conservation biology." Trends in Ecologyand Evolu global scale, synergy among the distinct proximate causes adds up to tion 11: 193-96. IIlOI"Cthan the sum of each individual cause. If one insists on a mini Barnosky, A. D. 1986. "'Big game' extinction caused by Late Pleistocene climatic malistic answer for what caused the late Quaternary extinctions, it change: Irish elk (Megalocel'osgiganteus) in Ireland." Quaternary Reseanh 25 : seems to be this: the actions of colonizing and expanding prehistoric 128-35. Barnosicy, A. D. 2001. "Distinguishing the effects of the Red Queen and Court hllmans (primarily hunting and habitat modification) seems omni Jester on Miocene mammal evolution in the northern Rocky Mountains:' pn.:scnt in the past global extinction (Brook et aI., 2007; Gillespie, Journal ofVertebl'ate Paleontology 21: 172-185 . OOH), but in many cases, species were left much more vulnerable be Barnosky, A. D. 2008. "Megafauna biomass tradeoff as a driver of Quaternary and (:lllSC of climate-induced range contractions and changes in habitat future extinctions." Proceedings ofthe National Academy ofSciences, USA 105: (JI':llity (Guthrie, 2006; Nogues-Bravo et al., 2008). 11543-48. The degree to which climate change was the "straw that broke the Barnosky, A. D. 2009. Heatst1'Oke: Nature in an Age ofGlobal Warmil'!5 . Washing 'LI,)I IiI ~.lInd's back" probably differed to some extent for each species of ex ton, D.C.: Island Press. riIll:t Quaternary megafauna, and will only be really understood after Barnosky, A. D., and E. L. Lindsey. 2010. "Timing of Quaternary mega faunal ex (ktailed study of each extinct species (Koch and Barnosky, 2006). 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A. 101lIlill/II('/i,' l,il//lI'II/I SO/'1"' 1' 1.11, II ' I I ' 11,,, kllllll , .111111, II ';"101,, '1111 " 111111111'.1I1i '1'"II:lIlIl.rI ~'sl i lhlillll ""i1I1' I'IX EVTDENCE FROM THE PAST Pleistocene Darling Downs, eastern Australia: The promise and pitfalls of dating as a test of extinction hypotheses:' Quaternary ScienceReviews 30: 899 Chapter 12 l) 14. 1',"Jt,allx, G. J., J. A. Long, L. K. Ayliffe, J. c. Hellstrom, B. Pillans, W. E. Boles, M . N. Hutchinson , et al. 2007a. "An arid-adapted middle Pleistocene vene Tropical hrate fauna from south-central Australia:' Nature 445: 422-25 . Quaternary Plant Extinction: I', id(';IUX , G. J" R. G. Roberts, D . Megirian, K. E. Westaway, J. c. Hellstrom, and J. I. Olley. 2007b . "Mammalian responses to Pleistocene climate change in A PaleoecologicalPerspective from ,~()lItheasternAustralia:' Geology 35 : 33-36. 'ill'lli:lI, W, P. J. Crutzen, and J. R. McNeill. 2007. "The Anthropocene: Are hu the N eotropics I\\an~now overwhelming the great forces of nature?" Ambio 36: 614-21. 0.;111,11'1, A. J., P. A. Kosintsev, T. F. G. Higham, and A. M. Lister. 2004. "Pleis MARK B. BUSH AND NICOLE A. S. MOSBLECH locene to Holocene extinction dynamics in giant deer and woolly mam ,"oth:' Nature 431: 684-89. Slirovell, T., N. Waguespack, and P. J. Brantingham. 2005 . "Global archaeological I.:vidcnce for proboscidean overkill:' Proceedings ofthe National Academy ofSci t'nce.\~USA 102: 6231-36. 'I·!tomas, C. D., A. Cameron, R. E. Green, M. Bal films ~f'theRoyal Society ofLondonB 325: 479-88. ics within the Quaternary, Examples ofextinctions over longer periods Wt'Sl, ( •. g" and J. H. Brown. 2005. "The origin of allometric scaling laws in biol of time are readily documented within the fossil record, with the loss ogy I'i'om genomes to ecosystems: Towards a quantitative unifYing theory of' ofwhole families evident between Eocene and modern times (Morley, hiolvgical structure and organization:' Journal of Experimental Biology 208 : 2000, 2007). Herein lies a clue to the problem of detecting extinction I S7S- 92. of tropical plants-the ta.,'(onomic resolution of the fossil record. Willi,~,K. )., K. D. Bennett, and D. Wall(er, 2004. ''The evolutionary legacy ofthr Most of the paleobotanical records that we have from the tropics I.'r Ages:' Philosophical Transactions ofthe Royal Society ofLondon B - Biologicfll are based on fossil pollen, plus a few on wood, and even less on seeds SI'i1'1'I/:CS ~59:157-58 . ,1l1dother macrofossils. With a few exceptions, fossil pollen identiflCa W" 11' , S. , ;Ind J. Field. 2006. "A review of the evidence for a human role in the ex tions are at the genus or family level, and so an extinction sufficient to I illt'l iOIl of Australian megafauna and an alternative interpretation?' Quat/:I' remove an entire genus would be the minimum detectable level of lilli '\, Science Reviews 25: 2692-703 . 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 ,IIIe )In : !' rill1csc lic e)f 1'11('( JII;lr~ TI1:11' )'. We can sec at that scale that major i lilll :lli c ( Will'S :1t1d SI't'\':ld "i' lin' inil i:lrcd cycles of species loss and 'IP"i ' i :llil)tl , II is 111)1 1I111'1',I!a)ll.lhk '" SIIPpCl.~~'rhar the spread of fire II)"