Boundaries for biodiversity: the implausible science of a ’safe operating space”

Posted on: 17 November 2017

A new international study suggests the notion of a planetary boundary for biodiversity and the recent attempts to fix it are vague and encourage harmful policies. The study suggests an alternative based on the increasing insights into the connections between biodiversity and ecosystem functioning and stability.

The study, recently published in the peer-reviewed journal Trends in Ecology and Evolution, poses the question of how we should manage human actions that harm biodiversity.

One solution embraces the notion of planetary boundaries, arguing that global environmental processes quite generally have “tipping points.” These are catastrophes involving thresholds beyond which there will be rapid transitions to new states that are very much less favourable to human existence than those presently. The associated notion is that humanity’s business as usual can only continue so long as it remains within some “safe operating space”.

Drawing attention to global environmental issues is certainly essential, so what harm is there in this approach — even if it has scientific limitations?

“The problem is that the notion of planetary boundaries for biodiversity adds no insight into our understanding of the threats to biodiversity and ecosystem functioning, has no evidence to support them, is too vague for use by those who manage biodiversity, and can promote harmful policies,” said Professor Jose M. Montoya, from the French National Centre for Scientific Research, at the Theoretical and Experimental Ecology Station in Moulis.

“Take the boundary definition. The original idea was to use extinction rates. Certainly, there would be local consequences of species loss, but why a precipitous collapse of ecosystems? Neither theory nor empirical data support any threshold of biodiversity below which ecosystem function is compromised.”

“Confronted with these fatal flaws to the original idea, there has been a proliferation of new indices. They add no useful insight. Even were we able to estimate the necessary numbers, the definition of the threshold is entirely arbitrary.”

The Floreana mockingbird now numbers fewer than 150 individuals.  Its extinction would be a tragedy, not least because it was one of four species of mockingbird on the Galapagos that gave Charles Darwin his first clues about evolution.  But were it to become extinct, it is not clear how that would lead to massive ecosystem collapse on the far side of the planet. Image credit: Professor Stuart L. P

Professor Ian Donohue, from Trinity College Dublin, who co-authored the study, said: “Fatally, the boundaries framework lacks clear definitions, or it has too many conflicting ones, does not specify units, and fails to define terms operationally, which prohibits it being applied by those who set policy or manage natural resources.”

There are acute moral hazards associated with this flawed worldview. First, because there is no operational definition of safe operating space, people have argued that human actions were once environmentally either benign or allowed for recovery. But worse still, people can intimate that if the planet isn’t obviously collapsing around us then surely we can continue to deplete it.

Professor Donohue added: “If we suggest a catastrophe has happened and the consequences are not evident, then how will managers and policy makers trust the science we do? When bad science informs policies, its future credibility is compromised.”

So how can environmental science sensibly inform those who manage and set policies for the complexity found in the natural world? The authors suggest a way forward: to address how biodiversity loss affects different elements of ecosystem change.

For instance, how can the functioning of ecosystems and their associated services to humans persist in the face of climatic change, particularly when local extinctions reduce the resistance of ecosystem productivity to climate extremes? This is an illustrative example of how ecosystem change is gradual, and inextricably tied to biodiversity loss.

“Fortunately, mounting evidence demonstrates how biodiversity loss alters the provision of functions, and the stability of ecosystems. We can now assess and monitor how losses in biodiversity affect different ecosystems. This in turn allows determining the effectiveness of a given environmental policy. The focus must be on appropriate scales and variables we can measure operationally and that tie to pressing practical problems,” said Professor Stuart L. Pimm, from Duke University (USA), co-author of the study.

“Good policy means we have no option but to understand the necessary complexity of nature in the environments we are starting to unravel. But acknowledging such complexities is not enough. We need the particulars: what aspects of ecosystem change we aim to minimise. Which species are vital to which processes and how these connect to human social and economic systems,” concluded Professor Montoya.

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