Can ecosystems malfunction?

We are told the natural world is ‘breaking down’. But forests don’t work like airplanes or human hearts

Jarno Verdonk/Getty Images

is Regents’ Professor in the Odum School of Ecology and director of the Center for the Ecology of Infectious Diseases, both at the University of Georgia in the US.

Edited byCameron Allan McKean

The Amazon rainforest, according to a 2021 study, is losing its capacity as a carbon sink and now emits more than it absorbs. In the tropics, marine scientists are reporting that coral reefs are in decline, threatening fish stocks. Equally concerning is research into the Atlantic Meridional Overturning Circulation, a vast system of ocean currents that helps regulate the climate and is at risk of collapsing this century. The entire global ecosystem appears to be losing its ability to function.

We find this view in newspapers, magazines, technical reports and the journals of learned societies. But thinking about the environment in terms of its functions is also how many of us tend to understand the world. We may think that forests exist to produce oxygen, wetlands to filter water, and bees to pollinate our crops.

There is a problem with this way of thinking: ecosystems don’t exist to perform goals. The Amazon absorbs carbon, but it doesn’t ‘aim’ to do so. It simply exists. Any standards of operation we find in nature have come directly from our own desires for things like climate stability, abundant fisheries, beauty or cultural meaning.

So why do we keep thinking ecosystems have functions they could fail to perform?

I came to this puzzle as a graduate student in the late 1990s, a time when research into biodiversity and ecosystem function was rapidly increasing. Initially, I thought I would write my dissertation on a conventional ecological topic: whether species richness drives productivity. Instead, I fell in with the philosophy of science crowd, attended their seminars, and eventually earned a master’s degree in philosophy alongside my work in ecology. There I encountered a rich debate over the concept of function – what it means, when it applies, what work it does. But no one seemed to be connecting that debate to the way ecologists were using the same word, unreflectively, to describe what ecosystems do. This essay is an attempt to bring those conversations together.

However, my concern with ecosystems and function was never just academic. I am an environmentalist, unsettled by the loss of natural places. And as a father, I am concerned that my generation will leave to our children a planet depleted in both richness and resilience. These commitments also drive my interest in debates about function. If the way we think about ecological crisis is conceptually shaky, we risk obscuring what’s really at stake.

I worry that the ways we often conceive of the problems before us are inadequate. For if ecosystems have no intrinsic ends and cannot truly ‘break down’, then how do we repair them? How do we respond to environmental crises in a world of aimless ecosystems?

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Approaches to conservation have long been shaped by debates about whether nature has a purpose or whether we are projecting our own aims onto it. Behind every attempt to justify new protections lies an implicit answer to the question: what is the environment for?

In the United States and the United Kingdom during the 19th century, these answers were rooted in game laws and hunting traditions that sought to maintain populations of species valued for sport or resource use. By the mid-20th century, the American forester and early conservationist Aldo Leopold offered a more expanded answer by proposing that our moral community should include ‘the land’ itself: soils, waters, plants and animals. In the 1970s and ’80s, the answers of conservationists were increasingly grounded in the intrinsic value of specific species, reflected in legislation such as the US Endangered Species Act. But a decade later, the species-focused approach of ‘conservation biology’ was seen by many as lacking. It targeted only rare organisms that contributed little to the circulation of their ecosystems – species like the spotted owl and the snail darter fish. In doing so, some researchers worried that the species approach might have overlooked more consequential concerns, such as the major ‘services’ provided by ecosystems, such as food production, clean water, drought mitigation, storm protection, timber and fibre.

The answer to ‘What is nature for?’ had become this: nature is for the services it provides to people

In the late 1990s, this crisis led to a new research agenda, which crystallised around ‘biodiversity and ecosystem function’ (BEF). This approach presented itself as a scientifically rigorous framework while simultaneously serving as a rhetorically powerful justification for conservation. In contrast to a hyper-focus on individual populations of rare species, BEF embraced all biodiversity, a holistic value.

In the early decades of the 21st century, this logic scaled up. The Millennium Ecosystem Assessment (2005) embedded an ecosystem services framework in international policy. The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services adopted a similar structure. National governments began commissioning natural capital accounts, attempting to assign monetary value to pollination, flood regulation, carbon storage and other ecological phenomena. The answer to the question ‘What is nature for?’ had become this: nature is for the services it provides to people. The language of ecosystem function was the conceptual bridge that made this answer sound scientific rather than merely political.

As a result, the idea of function now pervades how ecosystems are described and understood. Consider for a moment how you think about the ecosystems around you. If you have ever described a forest as a carbon sink or a wetland as a natural filter, you have inherited the ethic of BEF. If you’ve ever thought of a rainforest as something that provides oxygen for humans, or a reef as something that helps provide us with protein (in the form of fish), you’ve inherited the logic of ‘ecosystem services’.

What do we mean when we use the word ‘function’? Sometimes, it refers to designed purposes. For example, when we say that the function of a clock is to tell time, or the function of a carburettor is to mix air and fuel for combustion. In these cases, the object (or one of its parts) was intentionally made for a specific end. The same logic applies up a hierarchy of wholes and parts: the carburettor is part of the engine, the engine part of the car, the car part of a transport system.

Other kinds of functions arise through co-option rather than design. Writing at a picnic table, I might use a book or a rock to keep my papers from blowing away. The rock was not designed and the book was intended for another purpose, yet both can serve the goal I have in mind. I give them their function by using them in a certain way.

Still other functions emerge without any intention, particularly in nature. The philosopher Karen Neander offers a striking example: penguins are myopic on land. Their eyes are not defective but optimised for underwater focus, where penguins feed. Land myopia is a byproduct of a visual system shaped for a different environment.

Though there are several ways that ‘function’ is used, there are two main theories that guide (and justify) the ways scientists typically think about it: causal role theory and selected effects theory.

Everything exists for something else, from this perspective

Robert Cummins developed the causal role theory in response to Ernest Nagel’s argument in The Structure of Science (1961) about how science should avoid teleological language. That is, scientists should not explain things in a way that suggests the influence of specific goals or purposes. Such explanations appear to directly conflict with the scientific aim of explaining things in terms of laws. Nagel tried to explain that functional claims can and should be made without reference to goals or purposes. For example, rather than saying: ‘The function of the lungs is to oxygenate the blood,’ Nagel might say: ‘Given the structure of lung tissue, the properties of gases, and the pressure differences during breathing, oxygen diffuses into the bloodstream and carbon dioxide diffuses out.’ This becomes a scientific explanation based on laws and initial conditions. Cummins, however, thought this missed how scientists actually think about function. He saw that references to function could be a useful explanatory shortcut when talking about how things work, and so proposed a different approach. According to Cummins’s argument, ascribing function to anything is simply a way of identifying a component’s contribution to the ‘capacity’ of the system that contains it. Functional language, from this view, is fine. For example, the carburettor in a car enables the engine to convert chemical energy to mechanical energy; the engine enables the car to transport passengers; and so on.

It is easy to see why this theory would be attractive to ecologists who are typically interested in........

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