Nature's capacity to 'bounce back' when species are lost is vastly overestimated

The idea that ecosystems carry plenty of backup, so if a small number of species become extinct there is little harm, has been greatly overestimated, according to the largest global study of its kind.

New research led by King's College London and Imperial College London warns that a lack of biodiversity could threaten people's food security and climate protection, as diverse ecosystems provide a wide range of benefits that people depend on, including pollination, water purification, carbon storage and natural pest control.

The study, by King's College London and Imperial College London with the Natural History Museum and The Alan Turing Institute, has found that ecosystems have far less "spare" capacity than previously thought, with the ocean potentially having the most to lose.

Biodiversity benefits rarely level off

The study, published in Nature Ecology & Evolution, combined 423 published studies and 222,829 data points across land, freshwater, marine and estuarine ecosystems, producing a database more than twice the size of the largest previous effort and the largest of its kind.

Across 23 categories of ecosystem services and functions, most benefits rose steadily with biodiversity rather than leveling off once a handful of species were present. The findings suggest that functional redundancy—the idea that species can substitute for one another, so losses do little harm—has been overestimated.

Dr. Emma Moffett, study lead and lecturer in geography at King's College London, said, "Our findings challenge the comfortable assumption that ecosystems carry plenty of backup, so losing a species here and there doesn't change much. Across most of the benefits ecosystems provide that we looked at, the data doesn't support that. The ecological benefits keep climbing as diversity rises, which means they fall as we lose species."

Ocean carbon storage depends on diversity

Ocean carbon sequestration, the process of capturing and storing carbon dioxide (CO₂) from the atmosphere in marine waters and sediments, showed by far the strongest positive response to biodiversity of any service measured.

This indicates that so-called blue carbon sinks—the ocean and coastal ecosystems such as coral reefs, salt marshes or mangroves that capture and store carbon dioxide from the atmosphere—depend on sustaining diverse marine communities, from phytoplankton to the microbial food webs that pump carbon into deep water.

The authors caution that this result rests on a small number of data sets and identify it as an urgent gap in current knowledge.

Moffett goes on to say, "The ocean result stopped us in our tracks. Carbon capture at sea responded to biodiversity more strongly than anything else we measured, and yet it's one of the least studied areas we found. If the world is counting on blue carbon to help with climate change, marine life can't be an afterthought."

Not all services depend on diversity

Some ecosystem services proved exceptions. Protection against hazards such as coastal flooding and erosion was relatively insensitive to biodiversity overall, because it often depends on one or two foundational species, such as the shrubs that stabilize sand dunes. The authors argue that conservation must therefore balance maintaining overall diversity with safeguarding irreplaceable foundational species.

Dr. Will Pearse, an associate professor of evolutionary ecology in the Department of Life Sciences at Imperial College London, said, "We've known that biodiversity supports humanity by providing us with food, clean water, clean air and so many other ecosystem services. But what this model gives us is a precise, global picture: We can now predict the benefits biodiversity provides anywhere, making it even easier to recognize and take advantage of those benefits."

The full database and model forecasts across all 23 ecosystem service and function categories are publicly available to support policy and planning.

The team also used the database to look ahead, linking it to biodiversity projections under the socioeconomic scenarios used by the Intergovernmental Panel on Climate Change.

The researchers' model predicts that biological pest control on farmland, delivered free by the natural enemies of crop pests, declines under a fossil-fuel-driven development path compared with one with less fossil fuel, with the sharpest losses in countries experiencing rapid population growth and lower levels of development.