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 HAL Id: hal-02404725 https://hal-univ-tlse3.archives-ouvertes.fr/hal-02404725v2 Submitted on 26 Oct 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Forum 10-fold background. Despite widespread To address concerns that extinction rates Planetary Boundaries criticisms, the tipping-point claim per- are an inappropriate metric, the biodiver- for Biodiversity: sists, with recent reproduction of the orig- sity boundary is renamed as ‘biosphere ii inal claim [1] and statements that the integrity’ [3]. Two static measures of bio- Implausible Science, threshold is ‘not arbitrary’, emerges from diversity replace rates: phylogenetic vari- Pernicious Policies ‘massive amounts of data’ from many ability and functional diversity. Problems 1, fields, and that ‘no one is saying that of definition apart, reliable estimates for José M. Montoya, * ’ ‘ 2 the idea is wrong , despite massive anything resembling these are impossible Ian Donohue, and ’ 3 breakthroughs in counting extinctions . to obtain at regional to global scales. Stuart L. Pimm As we explain in Box 1, none of these statements are justified. Confronted with the inappropriateness of The notion of a ‘safe operating their measures, we are urged to keep space for biodiversity’ is vague Drawing attention to global environmen- using ‘in the interim’ extinction rates – and encourages harmful policies. tal issues is certainly essential, therefore already shown to be flawed – and a ‘bio- fi Attempts to x it strip it of all mean- what harm is there in another approach, diversity intactness index’ [3]. The latter is fi ingful content. Ecology is rapidly super cially attractive, even if it has the average abundance of a broad range gaining insights into the connec- limitations? We show that notions of of species relative to their abundance in planetary boundaries add no insight into an undisturbed habitat. The boundary is tions between biodiversity and eco- our understanding of the threats to set at >90%, assessed geographically system stability. We have no option biodiversity and ecosystem functioning, across biomes or other large areas. This but to understand ecological com- have no evidence to support them, are proliferation of indices adds no useful plexity and act accordingly. too vague for use by those who manage insight. Even if we were able to estimate biodiversity, and promote pernicious the necessary numbers, their limits are How Should We Manage Human policies. Attempts to fix these problems arbitrary. Actions That Harm Biodiversity? strip the original idea of all meaningful Human actions obviously harm the natu- content, but still plead for the notion Finally, the purported threshold occurs for ral world and, as we reduce the popula- of a safe operating space. Why is this the response variable of ‘biosphere func- tions of species and drive some to deeply flawed idea so seductive, tioning’. Neither theory nor empirical data extinction, we change ecosystems. and what problems arise from its support any threshold of biodiversity How best should environmental science embrace? below which ecosystem function is articulate its concerns, set research agen- das, and advise policies? One solution Box 1. Why Tipping Points for Biodiversity Are Fatally Flawed embraces the notion of planetary bound- The critical global extinction rate is operationally undefined: when the heart of the last individual of a species aries [1] arguing that global environmental stops beating, global extinction rate spikes momentarily. Why should this lead to planetary collapse? ‘ processes very generally have tipping Suppose we define the rate ourselves – for example in terms of extinctions per million species [2] averaged per year or decade. Following the discovery of the Hawaiian Islands by the Polynesians 1500 years ago, they points’. These are catastrophes involving eliminated so many species that even the decadal global extinction rate would have been exceptional. thresholds beyond which there will be However, why would these extinctions of island endemics cause a collapse that putatively is both global and rapid transitions to new states that are only now visible? There would certainly be local consequences of species loss, but why a precipitous local very much less favorable to human exis- collapse in ecosystems and why would it be global in extent? Furthermore, how might the rate of loss (versus its size) be responsible? tence than current states. The associated notion is that humanity’s ‘business as Certainly, there are regional physical processes for which empirical data suggests thresholds. Globally their usual’ can only continue so long as it existence is far from certain; they do not exist within the terrestrial biosphere in isolation [12]. Models of single remains within some ‘safe operating populations and local communities can show thresholds, but these neither deal with extinction rates nor i,ii space’ . global processes. ii Indeed, in publications [3], though not in presentations , planetary boundary arguments have moved away The rate of human-caused extinctions – from catastrophes, first to rapid transitions, where small changes lead to large effects, then to more gradual now 100–1000-fold the natural back- ones. The concession is ‘not all Earth system processes included in the planetary boundary have singular – ground rate [2] is one of two of the nine thresholds at the global/continental/ocean basin level’ [3]. Exactly so. This statement admits their arbitrary global processes deemed to have nature. If anything can happen, then there is no insight gained: gradual change is embraced by entirely arbitrary and indefinable values where the ‘safe operating space’ is transgressed. exceeded a purported tipping point of Trends in Ecology & Evolution, February 2018, Vol. 33, No. 2 71 compromised [4]. Defining a safe operat- species and the many species that hard, we will not need to understand its ing space for ecosystem function makes depend on them. details. We need not define measures, even less sense as the spatial scale and terms, processes, responses in opera- the number of functions analyzed Irrespective of spatial scale, the bound- tional ways. In short, ecological ignorance increases [5]. aries framework is ill-founded, inoperable, is bliss, if human actions remain within and can have unexpected detrimental limits. If Not Global Processes, Then effects on ecosystems. Local Ones? Reality is different. Nothing changed glob- ‘Nevertheless’, continue the arguments, The Dangers of a Flawed ally in 1989, and this local experience has ‘it is important that boundaries be estab- Worldview many precedents elsewhere, before and i lished for these processes’. Why? Per- In an informative example, Rockström after. This cod collapse was unfortunate, haps, although the planetary boundary reinforces his initial claims arguing that but overfishing is global, as appreciated framework might add no insights into the collapse of the Newfoundland cod since the 18th century, and the term was what we know about global human fishery in 1989 represents ‘a very precise first used (for cod) in 1855. Humans overf- impacts, then its practical utility to envi- tipping point’ of human actions trans- ished, overharvested, overgrazed, defor- ronmental managers might justify it. gressing global planetary boundaries. ested, polluted, and caused many other Fatally, the boundaries framework lacks Human actions were apparently within environmental ills long before 1989 and in clear definitions, or it has too many con- bounds before 1989. The year 1989 many other places. They have extermi- flicting definitions, does not specify units, was apparently ‘the boundary between nated substantial numbers of species and fails to define terms operationally, the Holocene and Anthropocene’ – a globally, and especially top predators, thus prohibiting application by those notion we find particularly specious. The across vast swaths of land and sea, who set policy or manage natural resour- facts are entirely prosaic: cod landings and have done so for tens of thousands ces. Moreover, recent reviews indicate averaged about 300 000 tons from the of years. that tipping points occur only rarely in late 1880s until the late 1950s, spiked at natural systems [6], while policies related over threefold higher in the 1960s, and Ways Forward to boundaries are unlikely to be evidence- the stock declined precipitously thereafter How then can environmental science sen- based. A need for operational definitions [9]. sibly inform those who manage and set to aid managers is self-evident [7]. policies for the complexity that is nature? First, there is an acute moral hazard. Elsewhere, we review 42 large organiza- At regional and local scales, managers Because there is no operational