A planetary boundary for biodiversity

Planetary boundaries
Source: Steffen et. al. Planetary Boundaries: Guiding human development on a changing planet. Science, 16 January 2015. Design: Globaïa
Feb 2015
6

Belinda Reyers reports on the expanded collaboration advancing the planetary boundaries framework.

The planetary boundaries framework, first published in 2009, introduced us to the possibility of distilling a complex Earth system – of land, oceans, atmosphere and life – into 9 global-scale dimensions responsible for keeping the Earth in its current hospitable state. The processes included in the planetary boundaries framework are climate change, biodiversity loss, land-system change, biogeochemical flows, stratospheric ozone depletion, ocean acidification, freshwater use, atmospheric aerosol loading, and chemical pollution. The authors worked to identify measures of each dimension, called control variables, and establish safe boundary zones in these measures, beyond which thresholds and abrupt or undesirable change might lie. The boundaries have been likened to avalanche warning signs, stepping off a kerb into traffic, lights on the dashboard of a car – they provide an early indication that we are approaching a potential threshold in a planetary process, beyond which we risk destabilising the Earth system. The framework has been effective in getting the environment onto the table at a variety of development fora and in bringing Earth-system knowledge to bear on the challenges of sustainability.

A recent update of the boundaries has just been published in Science. Based on advances and new contributions made over the past 5 years by various research communities, the update presents a number of enhancements including improvements in individual boundaries. While the 2009 paper focused on the identification of a consensus set of planetary processes, authors were only able to establish control variables and boundaries for well-known global-scale processes such as climate change, stratospheric ozone, and ocean acidification. For the remaining boundaries, their regional scales of operation; lack of global datasets; and/or uncertainty around their interactions with the way the Earth system functions made the original paper reliant on placeholder variables and interim boundaries – a clarion call to scientists to contribute to the further development of these planetary boundaries.

And this is precisely what the DIVERSITAS community (an international programme of research on biodiversity) did with the biodiversity loss boundary – convening a workshop of biodiversity scientists from around the world with colleagues from the International Geosphere-Biosphere Programme (IGBP) well-versed in the planetary boundaries work. Foreshadowing the kinds of collaboration envisaged by Future Earth, a few heady days in early 2012 were spent pondering the ecosystem in the Earth system, the wonderful – but daunting – complexity of biodiversity, and the possibility (or not)  of global-scale thresholds. The resultant paper by DIVERSITAS colleagues and partners – which finally surfaced in 2014 – clarified weaknesses in the species extinction-rate boundary proposed in the original paper and put forward alternative approaches to determine biodiversity loss boundaries at global and sub-global scales. The Science publication uses these alternatives to develop what is now called the biosphere integrity boundary. It follows the DIVERSITAS publication in highlighting that the biosphere - the fabric of life on earth made up of organisms of animals, plants, fungi, microorganisms and their ecosystems - plays two key roles in keeping the Earth system in a safe space. The first role – the functional role - recognises the enormous importance of the biosphere in cycling nutrients, chemicals, materials, waste and energy through the Earth system – by so doing removing pollutants from the water and air, regulating the climate, fertilising soils and much more. The second role, played by the genetic material making up the biosphere, allows the biosphere to persist and adapt under changing conditions, thus perpetuating these functions into the future and making the Earth system more resilient to change.

As usually happens at the global scale, ideas precede data, and so the Science paper falls back on global extinction rates (with caveats and updated thresholds) to capture genetic diversity and its role in supporting Earth system resilience to change. In exploring the functional role this new work presents an example of possible new approaches at sub-global and biome scales. Further new measures are imminent thanks to the efforts of communities such as DIVERSITAS and their core projects now transitioning into Future Earth. Similar advances are also clear in several of the other boundaries with contributions from other projects within Future Earth, such as the major update to the biogeochemical boundary, which draws on the work of Steve Carpenter (PECS) and Elena Bennett (EcoServices).

One of the most significant outcomes of the DIVERSITAS contribution to the biosphere integrity boundary was the concluding realisation in the GEC paper that “biodiversity’s role in supporting a safe operating space for humanity may lie primarily in its interactions with other boundaries, suggesting an immediate area of focus for scientists and policymakers” (Figure 1). The biosphere, through its interactions with Earth system energy, nutrient and material cycles, plays a role in – and is affected by – climate change, biogeochemical flows, freshwater use and other of the planetary processes. Managing the biodiversity boundary can therefore play a role in slowing or preventing crossing of the other boundaries, and conversely the biosphere risks being pushed closer to its boundary by changes in other planetary processes.  This interactive nature of the boundaries is also more obvious in the updated planetary boundaries framework which now recognises the “core” role of biosphere integrity and climate change through their interactions and feedbacks with the other seven boundaries.

Further enhancements to the planetary boundaries framework include a new two-level approach that now recognises the sub-global heterogeneity and regional scales of operation of some of the boundaries. This approach proposes sub-global level boundaries which – if transgressed – affect the Earth System at a global scale. Three boundaries: biogeochemicals, freshwater use, and land-system change; now include both a global boundary value and regional distribution functions indicating where boundaries have been transgressed or not at regional scales (Figure 2).

The results of such interdisciplinary collaboration have the potential to really speed up the move towards the cutting-edge knowledge needed to make transitions to sustainability – part of the vision behind Future Earth. As the publication acknowledges, there is some way to go to bring the planetary boundaries into a truly interdisciplinary space. We have already seen the evolution from Earth System boundaries to ‘doughnuts’ that integrate measures of social justice, such as income and social equity, and with the help of platforms like Future Earth, hopefully onward to truly intertwined social-ecological science and practice.

Further reading

Steffen et al. 2015. Planetary Boundaries: Guiding human development on a changing planet. Science, January 2015. doi: 10.1126/science.1259855

Mace GM, Reyers B, Alkemade R, Biggs R, Chapin FS, Cornell SE, Dıaz S, Jennings S, Leadley P, Mumbyl PJ, Purvism A, Scholes RJ, Seddon AWR, Solan M, Steffen W and Woodward G. 2014. Approaches to defining a planetary boundary for biodiversity. Global Environmental Change. 28:289-297.

read more on sciencedirect.com

Rockström, J., W. Steffen, K. Noone, Å. Persson, F. S. Chapin, III, E. Lambin, T. M. Lenton, M. Scheffer, C. Folke, H. Schellnhuber, B. Nykvist, C. A. De Wit, T. Hughes, S. van der Leeuw, H. Rodhe, S. Sörlin, P. K. Snyder, R. Costanza, U. Svedin, M. Falkenmark, L. Karlberg, R. W. Corell, V. J. Fabry, J. Hansen, B. Walker, D. Liverman, K. Richardson, P. Crutzen, and J. Foley. 2009. Planetary boundaries:exploring the safe operating space for humanity. Ecology and Society 14(2): 32. http://www.ecologyandsociety.org/vol14/iss2/art32/

Rockström et al. A safe operating space for humanity, Nature, 23 September 2009, doi: 10.1038/461472a

--------------------------------------------------------------------------------

This article was updated on 6 February to correct Figure 1 from an earlier version.

Comments

Daniel P Faith9 Mar 2015
Planetary boundaries: genetic, phylogenetic and functional trait diversity Belinda Reyers’ blog “A planetary boundary for biodiversity” shows that there is much interesting work still to be done on a “biodiversity” planetary boundary. It is constructive to have a call for more collaboration on this within Future Earth. It’s timely now to consider the early work – and the more recent work - by bioGENESIS, one of the core projects (http://www.futureearth.org/projects ) now transitioning into Future Earth . This covers two key aspects for a biodiversity boundary – genetic/phylogenetic diversity and functional traits diversity (Steffen et al 2015). 1) genetic/phylogenetic diversity bioGENESIS (Faith et al 2010) first proposed a planetary boundary for biodiversity, based on phylogenetic diversity (called “PD”): “....Tipping points may take into account longstanding pressures, with delayed impacts on biodiversity. Figure 3 provides a hypothetical illustration of what this means for the loss of evolutionary history (PD), as extinctions continue within a taxonomic group. The plot shows that successive species extinctions each may imply only a moderate loss of PD, until, abruptly, the last species goes extinct — and the long branch, representing a large amount of PD, is lost. A nominated ‘boundary’ could reflect the degree of acceptable risk to evosystem services relative to this tipping point. An approach called ‘phylogenetic risk analysis’ [Faith 2008] provides exactly this kind of risk assessment. For instance, one can study ‘worst-case losses’ that arise when one or more entire branches of the phylogenetic tree are lost. Phylogenetic risk analysis can guide decisions that try to reduce risk of these tipping point outcomes.” This proposal for phylogenetic diversity tipping points and boundaries highlighted evolutionary or evosystem services, including option values and evolutionary potential (Faith et al 2010; see also Mace et al 2014). Such option values of biodiversity typically reflect global-scale benefits for future generations, and so they are a natural consideration for planetary boundaries. At the same time, phylogenetic diversity represents current variation with current uses and benefits, at local to global scales, and at these scales may link to other planetary boundaries. Co-lead, Felix Forest, and other members of bioGENESIS recently organised a symposium, and special issue of Phil. Trans. R. Soc. B, that explores some of these issues (Forest et al 2015). One contribution (Faith 2015) summarises the task ahead for bioGENESIS within Future Earth: “…The species level and breeds level phylogenies equally highlight the issues of worst-case losses and tipping points. These PD tipping points all involve a threshold that is crossed when the last descendant of a long phylogenetic branch is lost, producing a large irreversible biodiversity loss….This is now a key topic for bioGENESIS, a programme focused on the role of evolutionary biology in multi-disciplinary biodiversity science, and the organizer of this Discussion Meeting. bioGENESIS is now part of Future Earth (http://www.futureearth.info/), a new global research programme focused on global environmental change and global sustainability. Among the key goals of Future Earth is ‘observing, explaining, understanding, projecting earth, environmental and societal system trends, drivers and processes and their interactions; anticipating global thresholds and risks’. One focus is on providing early warnings of boundaries and tipping points, and how these impact on human well-being. PD tipping points will be an important aspect of this work, given its links to feature diversity and option values underlying human well-being.” Early warnings with respect to a PD planetary boundary may focus on the changing status of “phylogenetic Key Biodiversity Areas” – those places on the planet that are outstanding in their current contribution to retaining global phylogenetic diversity (see our paper in collaboration with IUCN; Brooks et al 2015). Much of that work is among species, across many taxonomic groups. The rationale extends to phylogenetic models describing variation among key crops and animal breeds (Faith 2015). It also extends more generally to within species variation. PD, when applied to a phylogenetic summary of within-species genetic variation, provides support for a “power curve” model (analogous to the species-area relationship) relating fractional loss of species range to fractional loss of its genetic diversity (bioGENESIS paper, Mimura et al in revision). With another bioGENESIS stakeholder, GEO BON, we are exploring how a simple life history classification of species can assign the parameters (z value) of the power curve. This may allow us to produce, for many species, an ongoing global report card on loss of genetic diversity, building on existing efforts (e.g. Map of Life) to monitor change in range extent of species. This adds another potential level of analysis to our work on global change and planetary boundaries. 2) functional traits diversity PD is perhaps the most useful phylogenetic measure as a basis for a biodiversity planetary boundary (an alternative measure, PSV, mentioned by Mace et al and Steffen et al, actually can increase when a species goes extinct). However, PD does not tell us all we need to know about functional traits. bioGENESIS is exploring ways to make general inferences about functional traits diversity (avoiding conventional approaches based on nomination of a few favourite traits). The idea is to be able to make inferences about more general functional trait diversity (including losses, tipping points, risk analyses and so on), analogous to the way phylogeny allows inferences about general feature diversity. One possible framework (called “EDf”) “allows analysis of a wide variety of features or characters of species to derive a functional trait space, enabling inferences about more general trait variation. …At the global scale, EDf then could provide, for multiple taxonomic groups, a running report card on the loss (or risk of loss) of functional trait diversity. This would nicely complement the emerging use of a PD report card to assess risks associated with resilience-loss, tipping points and ‘‘planetary boundaries’’” (Faith in press). BioGENESIS welcomes collaboration in exploring these potential contributions of evolutionary biology to research on global change and planetary boundaries. Dan Faith Ex-officio, bioGENESIS References Brooks TM, A. Cuttelod , D. P. Faith , J. Garcia-Moreno , P. Langhammer , S. Pérez-Espona (2015) Why and how might genetic and phylogenetic diversity and process be reflected in the identification of key biodiversity areas? Phil. Trans. R. Soc. B 2015 370 20140019 DOI: 10.1098/rstb.2014.0019 Faith, D.P., S. Magallón, A.P. Hendry, E. Conti, T. Yahara, and M.J. Donoghue (2010) Evosystem Services: an evolutionary perspective on the links between biodiversity and human-well-being. Current Opinion in Environmental Sustainability 2: 66-74. Faith DP (2015) Phylogenetic diversity and extinction: avoiding tipping points and worst-case losses from the tree of life. Phil. Trans. R. Soc. B 2015 370 20140011. DOI: 10.1098/rstb.2014.0011 http://rstb.royalsocietypublishing.org/content/370/1662/20140011.full?ij... Faith DP (in press) “The unimodal relationship between species’ functional traits and habitat gradients provides a family of indices supporting the conservation of functional trait diversity” Plant Ecology . http://link.springer.com/article/10.1007/s11258-015-0454-z Forest Félix, Keith A. Crandall, Mark W. Chase, Daniel P. Faith (2015) Introduction: Phylogeny, extinction and conservation: embracing uncertainties in a time of urgency. Phil. Trans. R. Soc. B 2015 370 20140002; DOI: 10.1098/rstb.2014.0002. http://rstb.royalsocietypublishing.org/content/370/1662/20140002 Mace GM, Reyers B, Alkemade R, Biggs R, Chapin FS, Cornell SE, Dıaz S, Jennings S, Leadley P, Mumbyl PJ, Purvism A, Scholes RJ, Seddon AWR, Solan M, Steffen W and Woodward G. (2014) Approaches to defining a planetary boundary for biodiversity. Global Environmental Change. 28:289-297. Steffen et al. (2015) Planetary Boundaries: Guiding human development on a changing planet. Science. doi: 10.1126/science.1259855