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Planetary Boundaries for Biodiversity
José Montoya, Ian Donohue, Stuart Pimm
To cite this version:
José Montoya, Ian Donohue, Stuart Pimm. Planetary Boundaries for Biodiversity: Implau- sible Science, Pernicious Policies. Trends in Ecology & Evolution, 2018, 33 (2), pp.71-73.
�10.1016/j.tree.2017.10.004�. �hal-02404725v2�
Forum
Planetary Boundaries for Biodiversity:
Implausible Science, Pernicious Policies
José M. Montoya,
1,* Ian Donohue,
2and Stuart L. Pimm
3The notion of a ‘safe operating space for biodiversity’ is vague and encourages harmful policies.
Attemptstofixitstripitofallmean- ingful content. Ecology is rapidly gaining insights into the connec- tionsbetweenbiodiversityandeco- systemstability.Wehavenooption buttounderstandecologicalcom- plexityandactaccordingly.
HowShouldWe ManageHuman ActionsThatHarm Biodiversity?
Humanactionsobviouslyharmthenatu- ralworldand,aswereducethepopula- tions of species and drive some to extinction, we change ecosystems.
Howbestshouldenvironmentalscience articulateitsconcerns,setresearchagen- das, and advise policies? One solution embracesthenotionofplanetarybound- aries[1]arguingthatglobalenvironmental processes very generally have ‘tipping points’.Thesearecatastrophesinvolving thresholds beyond which there will be rapid transitions to new states that are verymuchlessfavorabletohumanexis- tencethancurrentstates.Theassociated notion is that humanity’s ‘business as usual’ can only continue so long as it remains within some ‘safe operating space’i,ii.
Therateofhuman-causedextinctions– now 100–1000-fold the natural back- groundrate[2]–isoneoftwoofthenine global processes deemed to have exceeded a purported tipping point of
10-foldbackground.Despitewidespread criticisms, the tipping-point claim per- sists,withrecentreproductionoftheorig- inal claim [1] and statementsii that the thresholdis‘notarbitrary’,emergesfrom
‘massive amounts of data’ from many fields, and that ‘no one is saying that the idea is wrong’, despite ‘massive breakthroughs in counting extinctions’. As we explain inBox 1, none of these statementsarejustified.
Drawingattentiontoglobalenvironmen- talissuesiscertainlyessential,therefore whatharmisthereinanotherapproach, superficially attractive, even if it has limitations? We show that notions of planetaryboundariesaddnoinsightinto our understanding of the threats to biodiversity and ecosystem functioning, havenoevidence tosupport them,are toovagueforusebythosewhomanage biodiversity, and promote pernicious policies.Attempts tofix theseproblems strip the original idea of all meaningful content, but still plead for the notion of a safe operating space. Why is this deeply flawed idea so seductive, and what problems arise from its embrace?
Toaddressconcernsthatextinctionrates areaninappropriatemetric,thebiodiver- sity boundaryis renamed as ‘biosphere integrity’[3].Twostaticmeasuresofbio- diversityreplacerates:phylogeneticvari- ability andfunctionaldiversity.Problems of definition apart,reliable estimates for anythingresemblingtheseareimpossible toobtainatregionaltoglobalscales.
Confrontedwiththeinappropriatenessof their measures, we are urged to keep using ‘in the interim’ extinction rates – alreadyshowntobeflawed–anda‘bio- diversityintactnessindex’[3].Thelatteris theaverageabundanceofabroadrange ofspeciesrelative totheirabundancein anundisturbedhabitat.Theboundaryis set at >90%, assessed geographically acrossbiomesorotherlargeareas.This proliferation of indices adds no useful insight.Evenifwewereabletoestimate the necessary numbers, their limits are arbitrary.
Finally,thepurportedthresholdoccursfor theresponsevariableof‘biospherefunc- tioning’.Neithertheorynorempiricaldata support any threshold of biodiversity below which ecosystem function is
Box1.WhyTippingPointsforBiodiversityAreFatallyFlawed
Thecriticalglobalextinctionrateisoperationallyundefined:whentheheartofthelastindividualofaspecies stopsbeating,globalextinctionratespikesmomentarily.Whyshouldthisleadtoplanetarycollapse?
Supposewedefinetherateourselves–forexampleintermsofextinctionspermillionspecies[2]averaged peryearordecade.FollowingthediscoveryoftheHawaiianIslandsbythePolynesians1500yearsago,they eliminatedsomanyspeciesthateventhedecadalglobalextinctionratewouldhavebeenexceptional.
However,whywouldtheseextinctionsofislandendemicscauseacollapsethatputativelyisbothglobaland onlynowvisible?Therewouldcertainlybelocalconsequencesofspeciesloss,butwhyaprecipitouslocal collapseinecosystemsandwhywoulditbeglobalinextent?Furthermore,howmighttherateofloss(versus itssize)beresponsible?
Certainly,thereareregionalphysicalprocessesforwhichempiricaldatasuggeststhresholds.Globallytheir existenceisfarfromcertain;theydonotexistwithintheterrestrialbiosphereinisolation[12].Modelsofsingle populationsandlocalcommunitiescanshowthresholds,buttheseneitherdealwithextinctionratesnor globalprocesses.
Indeed,inpublications[3],thoughnotinpresentationsii,planetaryboundaryargumentshavemovedaway fromcatastrophes,firsttorapidtransitions,wheresmallchangesleadtolargeeffects,thentomoregradual ones.Theconcessionis‘notallEarthsystemprocessesincludedintheplanetaryboundaryhavesingular thresholdsattheglobal/continental/oceanbasinlevel’[3].Exactlyso.Thisstatementadmitstheirarbitrary nature.Ifanythingcanhappen,thenthereisnoinsightgained:gradualchangeisembracedbyentirely arbitraryandindefinablevalueswherethe‘safeoperatingspace’istransgressed.
TrendsinEcology&Evolution,February2018,Vol.33,No.2 71
compromised[4].Definingasafeoperat- ingspaceforecosystemfunctionmakes evenlesssenseasthespatialscaleand the number of functions analyzed increases[5].
IfNotGlobalProcesses,Then LocalOnes?
‘Nevertheless’,continue the arguments,
‘itisimportantthatboundariesbeestab- lished for these processes’. Why? Per- haps, although the planetary boundary framework might add no insights into what we know about global human impacts,then itspracticalutilityto envi- ronmental managers might justify it.
Fatally,the boundariesframework lacks cleardefinitions,orithastoomanycon- flictingdefinitions,doesnotspecifyunits, and fails to define terms operationally, thus prohibiting application by those whosetpolicyormanagenaturalresour- ces. Moreover, recent reviews indicate that tipping points occur only rarely in naturalsystems[6],whilepoliciesrelated toboundariesareunlikelytobeevidence- based.Aneedforoperationaldefinitions toaidmanagersisself-evident[7].
At regional and local scales, managers andconservation bodies are starting to abandon the boundaries framework.
Manyclaimthat theadoptionofbound- ariesandassociatedtippingpoints asa policygoalrisksbiodiversityconservation.
In the case ofEuropean forests,it pro- moted interventions that harmed biodi- versity [8]. Planting of ‘resilient tree species’ – to climate change, pests, and disease –and silviculture practices to promote such resilience – primarily thinning to encourage growth and to increase carbon storage – was recom- mendedtoavoidreachingatippingpoint in forest service provisioning, primarily timberproduction. Theserecommenda- tionsruncounter tobiodiversityconser- vation guidelines. They endanger old- growth forests, veteran trees, and rela- tively low-productivity native woody
species and the many species that dependonthem.
Irrespective ofspatial scale,the bound- ariesframeworkisill-founded,inoperable, and can have unexpected detrimental effectsonecosystems.
TheDangersofaFlawed Worldview
In an informative example, Rockströmi reinforces his initial claims arguing that the collapse of the Newfoundland cod fisheryin1989represents‘averyprecise tipping point’ of human actions trans- gressing global planetary boundaries.
Human actions were apparently within bounds before 1989. The year 1989 was apparently ‘the boundary between the Holocene and Anthropocene’ – a notionwefindparticularlyspecious.The facts are entirely prosaic: cod landings averagedabout 300 000 tons from the late1880suntilthelate1950s,spikedat over threefoldhigher inthe 1960s, and thestockdeclinedprecipitouslythereafter [9].
First, there is an acute moral hazard.
Becausethereisnooperationaldefinition of ‘safe operating space’, this not only encourages arguments that ‘growth within limits’i is acceptablebut also the belief that human actions were once environmentallyeitherbenign orallowed recovery.Worse still,ifthe planetis not obviously collapsing around us, then surelywecancontinuetodepleteit.
Second,ifwesuggestthatacatastrophe hastaken placeand the consequences arenotevident,thenhowwillmanagers and policymakers trustthe sciencewe do?Whenbadscienceinformspolicies, itsfuturecredibilityiscompromised.
Third,theplanetaryboundaryframework suggeststhatwecanviewnatureandits complexecologicalprocessesas atype ofblack box–if wedo notpokeit too
hard,wewillnotneedtounderstandits details. We need not define measures, terms, processes, responses in opera- tionalways.Inshort,ecologicalignorance is bliss, if human actions remain within limits.
Realityisdifferent.Nothingchangedglob- allyin1989,andthislocalexperiencehas manyprecedentselsewhere,beforeand after.Thiscodcollapsewasunfortunate, butoverfishingis global,as appreciated sincethe18thcentury,andthetermwas firstused(forcod)in1855.Humansoverf- ished,overharvested,overgrazed,defor- ested,polluted,andcausedmanyother environmentalillslongbefore1989andin many other places. They have extermi- nated substantial numbers of species globally, and especially top predators, across vast swaths of land and sea, andhavedonesofortensofthousands ofyears.
WaysForward
Howthencanenvironmentalsciencesen- sibly informthose whomanageandset policiesforthecomplexitythatisnature?
Elsewhere,wereview42largeorganiza- tionsdevotedtoglobalenvironmentman- agement and their various aspirational targets [7]. Weapplaud the Convention onBiological Diversity(CBD)andothers whentheydefinerigorousandoperational targets.Goodexamplesare17%ofland area and 10% of the ocean protected (CBD Aichi target 11), with the areas being ‘ecologically representative and well-connected’, ‘avoiding overfishing’ (target6), andpreventing‘theextinction ofknownthreatenedspecies’(target12).
Environmentalscientistsmustseekways toengagepolicymakerstoframealltheir otheraspirationssimilarly,becausesome arenotsoclearlydefined.
Attheheartoftheproblemaretermssuch as‘planetaryboundaries’,butalso‘sus- tainability’, ‘health’, ‘harmony’, and others, that are emotionally appealing 72 TrendsinEcology&Evolution,February2018,Vol.33,No.2
butrarely,ifever,defined.Theyallspeak to the urgent need to understand how human impacts change ecosystems, when at best weaspire to protect only halfofit.Wemustsetpoliciesandestab- lish management for the vast tracts of land and sea that we do not protect.
Fatally,those whodo sooften uselan- guage that does not borrow from the existing knowledge about ecosystem processes,norreadilytranslatesitsaspi- rationstothosewhostudythem[7].
Fortunately,mounting evidencedemon- stratesthepatternsandmechanismsby whichbiodiversitylossalterstheprovision offunctionsand the stabilityofecosys- tems. Wecan nowassess andmonitor howlossesinbiodiversityaffectdifferent ecosystems.Thisinturnallowstheeffec- tivenessofagivenenvironmentalpolicyto be determined. The focus must be on appropriate scales and variables that we can measure operationally. It must recognize and define the multiplicity of humanactionsandtheirconsequences.
Wemustcreatemutualtranslationsofthe termsused byempiricalecologists,the- oreticians, policymakers, and managers todescribethem[7].Thiswayforwardis sharedbyresearcherswithindifferentdis- ciplines: from those interested in the dynamics of socioecological systems [10] to those centered on biodiversity conservation[8].
Weknowmanyusefulthingsaboutthese issues,andtheoryandempiricalstudies mutually reinforce each other.We sug- gestawayforward:toaddresshowbio- diversitylossaffectsthedifferentfacetsof ecosystemchange [7] –resilience (how fast systems recover), resistance (how muchtheychange),variability(howmuch theyfluctuateovertime),andpersistence (howlongtheypersist).Thesemeasures of change are well-defined, have units, can be monitored over time, and can informmanagement.Theytietopressing practicalproblems.
Weprovidesomeexampleswhereeco- systemchangeisgradualbutisinextri- cablytiedtobiodiversityloss.First,what pollinators can we not afford to lose?
Regionaldeclinesinnativewildpollina- torscompromisethequalityandquan- tity of food crops that depend on pollination. Second, how well do spe- cies abundances resist harvesting or removaloftop-predators–aswehave done over much of the land and the oceans?Howcanwe ensurethatfish- eriesandotherexploitedresourcespro- vide reliable yields against a natural background of year-to-year variability, given economic drivers that require a minimum annual return and discount the future value of the stock? Third, howcanthefunctioningofecosystems andtheirassociatedservicestohumans persist in the face of climate change, particularly when local extinctions reduce the resistance of ecosystem productivitytoclimateextremes[11]?
Good policy means we have no option but to understand the necessary com- plexityofnatureintheenvironmentswe are starting to unravel. However, acknowledging suchcomplexitiesis not enough. We need the particulars – the aspects of ecosystem change that we aimtominimize.Whichspeciesarevital towhichprocesses,andhowthesecon- necttohumansocialandeconomicsys- tems. We must understand how economiclossesdependonthespecies involvedandtheecologicalcommunities in whichthey are embedded.We must alsounderstandthatthelossofanyspe- ciesisalossofculturalvaluesandposes significantmoralissues.
Therearelimitstogrowth.Whenweharm nature, environmental changes some- timeskickinimmediatelyandininevitably complexwaysthatdenythesimple and seductivenotionthat,withinsomelimited space,whateverthestressesweinflicton natureitwill beOK.We havenooption
buttounderstandthatcomplexity,make itoperational,andactaccordingly.
Acknowledgments
J.M.M.wassupportedbytheFrenchLaboratoryof ExcellenceProject‘TULIP’(ANR-10-LABX-41;ANR- 11-IDEX-002-02).
Resources
iRockström, J. (2015) Abundance with Planetary Boundaries.PresentationtotheInternationalInstitute forAppliedSystemsAnalysis (IIASA), March12th.
www.youtube.com/watch?v=1WFtCAdCm84
iiRockström, J. (2017) Beyondthe Anthropocene.
PresentationattheWorldEconomicForum,January 18.www.youtube.com/watch?v=V9ETiSaxyfk
1TheoreticalandExperimentalEcologicalStation,Centre NationaldelaRechercheScientifique(CNRS)University PaulSabatier(UPS),Moulis,France
2SchoolofNaturalSciences,TrinityCollegeDublin, Dublin,Ireland
3NicholasSchooloftheEnvironment,DukeUniversity, Durham,USA
*Correspondence:
josemaria.MONTOYATERAN@sete.cnrs.fr(J.M.Montoya).
https://doi.org/10.1016/j.tree.2017.10.004
References
1. WorldWildlifeFund(2016)LivingPlanetReport2016.Risk andResilienceinaNewEra,WWWInternational 2. Pimm,S.L.etal.(1995)Thefutureofbiodiversity.Science
269,347
3. Steffen,W.etal.(2015)Planetaryboundaries:guiding humandevelopment on a changing planet. Science 347, 1259855
4. Cardinale,B.J.etal.(2012)Biodiversitylossanditsimpact onhumanity.Nature486,59–67
5. Isbell,F.etal.(2011)Highplantdiversityisneededto maintainecosystemservices.Nature477,199–202 6. Capon,S.J.etal.(2015)Regimeshifts,thresholdsand
multiplestablestatesinfreshwaterecosystems;acritical appraisaloftheevidence.Sci.TotalEnviron.15,122–130 7. Donohue,I.etal.(2016)Navigatingthecomplexityof
ecologicalstability.Ecol.Lett.19,1172–1185 8. Newton,A.C.(2016)Biodiversityrisksofadoptingresil-
ienceasapolicygoal.Conserv.Lett.9,369–376 9. Hutchings,J.A.andMyers,R.A.(1994)Whatcanbe
learnedfromthecollapseofarenewableresource?Atlan- ticcod,Gadusmorhua,ofNewfoundlandandLabrador.
Can.J.Fish.Aquat.Sci.51,2126–2146
10.Dawson,T.P.etal.(2010)Dynamicpropertiesofcomplex adaptiveecosystems:implicationsforthesustainabilityof serviceprovision.Biodivers.Conserv.19,2843–2853 11.Isbell,F.etal.(2015)Biodiversityincreasestheresistance
ofecosystemproductivitytoclimateextremes.Nature 526,574–577
12.Lenton,T.M.andWilliams,H.T.(2013)Ontheoriginof planetary-scaletippingpoints.TrendsEcol.Evol.28,380– 382
TrendsinEcology&Evolution,February2018,Vol.33,No.2 73
