Ecosystems Have Far Less Spare Capacity Than We Thought, Global Study Finds

One of the most comforting ideas in ecology is that nature carries insurance. If a species disappears, the thinking goes, another one steps in to perform its role, and the ecosystem keeps functioning more or less as before. A sweeping new global analysis, led by researchers at King’s College London and Imperial College London together with the Natural History Museum and The Alan Turing Institute, suggests that this safety net is far thinner than scientists and policymakers have assumed. Published in Nature Ecology & Evolution, the study synthesised 423 published investigations and 222,829 individual data points spanning terrestrial, freshwater, marine and estuarine environments, making it more than twice the size of the largest comparable effort ever attempted and the most comprehensive of its kind.

The central finding is stark. Across 23 categories of ecosystem services and functions, most of the benefits that nature provides to humanity rose steadily as biodiversity increased, rather than levelling off once a handful of species were present. This pattern directly undermines the concept of functional redundancy, the long-standing assumption that species can readily substitute for one another, so that moderate losses of diversity do little measurable harm. Instead, the data show that ecological benefits keep climbing with every additional unit of diversity, which means, conversely, that they keep declining with every species lost. The comfortable buffer that conservation planning has often relied upon appears, in most cases, to be largely an illusion.

Dr Emma Moffett, the study’s lead author and a lecturer in geography at King’s College London, said the results challenge a deeply embedded assumption. Our findings challenge the comfortable assumption that ecosystems carry plenty of back-up, so losing a species here and there doesn’t change much, she explained. Across most of the ecosystem benefits the team examined, the data simply do not support that view. Because the ecological benefits continue to climb as diversity rises, they are falling as species disappear, and the consequences are likely to accumulate quietly until they become difficult to reverse. The implication for food security and climate protection is considerable, since diverse ecosystems underpin pollination, water purification, carbon storage and natural pest control, all services on which human societies depend daily.

Perhaps the most striking single result concerns the ocean. Ocean carbon sequestration, the process by which carbon dioxide is captured from the atmosphere and stored in marine waters and sediments, showed by far the strongest positive response to biodiversity of any service the researchers measured. This suggests that so-called blue carbon sinks, the ocean and coastal ecosystems such as coral reefs, saltmarshes and mangroves that draw down atmospheric carbon, depend critically on sustaining diverse marine communities, from phytoplankton at the base of the food web to the microbial networks that help pump carbon into deep water. If those communities are simplified by warming, acidification or overfishing, the ocean’s capacity to buffer climate change may weaken in ways that current models do not capture.

The authors are careful to note that the ocean result, while dramatic, rests on a comparatively small number of datasets, and they identify it as an urgent gap in current knowledge. Dr Moffett described the finding as one that stopped the team in its tracks. Carbon capture at sea responded to biodiversity more strongly than anything else measured in the analysis, she said, and yet it remains one of the least studied areas the team encountered. If the world is counting on blue carbon to help address climate change, she argued, marine life cannot be treated as an afterthought. The mismatch between the importance of the service and the paucity of data supporting it is itself a call to action for the research community.

Not every ecosystem service proved equally sensitive to diversity loss, and the exceptions are instructive. Protection against natural hazards such as coastal flooding and erosion was relatively insensitive to biodiversity overall, because this service often depends on one or two foundational species rather than on a broad portfolio of contributors. The shrubs that stabilise sand dunes, for example, deliver most of the protective benefit regardless of how many other species share the habitat. The authors argue that conservation strategy must therefore balance two distinct goals: maintaining overall diversity to preserve the many services that scale with it, and safeguarding irreplaceable foundational species whose loss would remove a single critical function outright.

Dr Will Pearse, an Associate Professor in Evolutionary Ecology in the Department of Life Sciences at Imperial College London, emphasised the practical power of the new synthesis. Biodiversity has long been known to support humanity through food, clean water, clean air and many other ecosystem services, he noted, but the model developed by the team delivers something more precise: a global picture that allows the benefits of biodiversity to be predicted anywhere on Earth. That predictive capability, he argued, makes it easier than ever to recognise those benefits and to take them into account in planning and decision-making. The full database and the model’s forecasts across all 23 categories of ecosystem services and functions have been made publicly available to support policy and planning at every scale.

The team did not stop at describing the present. They linked their database to biodiversity projections under the socioeconomic scenarios used by the Intergovernmental Panel on Climate Change, allowing them to look ahead at how ecosystem services might fare under different development pathways. One projection stands out for its immediate relevance to agriculture: biological pest control on farmland, delivered free of charge by the natural enemies of crop pests, declines under a fossil-fuel-driven development path compared with a scenario involving less fossil fuel use. The sharpest losses are projected for countries experiencing rapid population growth and lower levels of development, precisely the places least equipped to replace a free ecological service with costly chemical alternatives.

The technical achievement underlying these conclusions lies in the scale and consistency of the synthesis. By harmonising data from hundreds of studies across four broad ecosystem types, the researchers were able to test whether the relationship between biodiversity and ecosystem functioning, often demonstrated in small-scale experiments, holds at global scope and across real-world gradients of species loss. The answer, in most service categories, is that it does, and that the relationship is closer to a steady climb than to a plateau. That shape matters enormously for policy: if benefits saturated quickly, moderate biodiversity loss would be tolerable, but a steadily rising curve means every increment of loss carries a measurable cost in pollination, carbon storage, water quality and pest suppression.

For a world negotiating how much habitat it can afford to lose, the study reframes the question. The assumption of plentiful ecological back-up has allowed biodiversity loss to be treated as a secondary concern, something to be addressed once more urgent priorities are met. The new evidence suggests that the margin for error is much narrower than believed, and that the ocean, the planet’s largest carbon reservoir, may be the most biodiversity-dependent and least understood component of the entire system. As the authors make clear, the database and forecasts are now public, giving governments and planners the tools to quantify what is at stake. What remains is the political will to act on a finding that is, in essence, a warning: nature’s resilience has been overestimated, and the services it quietly provides are being spent faster than they can be replaced.

Subject of Research: Global synthesis of biodiversity-ecosystem service relationships across land, freshwater and marine environments

Article Title: Nature’s capacity to ‘bounce-back’ when species are lost vastly overestimated

Article References: Nature’s capacity to ‘bounce-back’ when species are lost vastly overestimated. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: biodiversity, ecosystem services, functional redundancy, blue carbon, ocean carbon sequestration, Nature Ecology & Evolution, King's College London, Imperial College London, climate change, pest control, conservation, IPCC scenarios