With species extinction rates up to 1,000 times higher than the natural rate, it is becoming urgent to understand the pressures on ecosystems and the consequences for our societies.
To discuss biodiversity loss, we asked Céline Bellard, a biologist and researcher at the CNRS, five questions. Her work focuses on conservation biology, biological invasions and biodiversity loss. Céline will explore the planetary boundary related to biodiversity, its root causes, its systemic impacts and the levers for reversing this trajectory.
1. How do we measure biodiversity and why does this remain a scientific challenge?
Measuring biodiversity is an extremely complex task due to the diversity of life forms and scales of analysis. As Céline Bellard points out, ‘one of the indicators is the number of species. But just counting species is a colossal task!’ This applies to terrestrial species as well as those in marine, underground and microbial environments. She also points out that the total number of species on Earth is estimated to be between 2 and 100 million, a range that shows how much remains unknown. But beyond simple counting, researchers are also interested in ‘biomass, abundance and even the role of species within ecosystems’.
This last dimension corresponds to functional diversity, i.e. the ability of a species to fulfil an ecological role (pollination, decomposition, predation, etc.). Céline also emphasises the importance of species communities, i.e. all the interactions between a species and others in its habitat: ‘Will it be prey, a predator, a resource, or a competitor?’ Each methodology thus captures a different facet of biodiversity, which makes mapping it all the more difficult.
2. Why do we talk about a ‘planetary boundary’ for biodiversity, and how is it quantified?
Biodiversity is now considered to be a planetary boundary that has been exceeded, i.e. a threshold beyond which the consequences become increasingly serious and difficult to control for ecosystems and human societies. The Stockholm Resilience Centre recently succeeded in quantifying this boundary using two main indicators: the rate of species extinction and the loss of genetic and functional diversity.
Céline Bellard explains that while ‘species extinctions are a natural phenomenon,’ current rates are ‘between 100 and 1,000 times higher than the rates found in fossil data.’ It is therefore the speed of extinctions that is worrying, as it prevents ecosystems from adapting or recovering. The biologist points out that this measurement includes ‘the loss of genetic diversity but also functional diversity’, i.e. the disappearance of key roles in ecosystems. Biodiversity is therefore not just a list of species: its degradation directly affects ecological balances and the services provided to humanity.
‘Nature is declining globally at a rate unprecedented in human history, and the rate of species extinction is accelerating, already causing serious effects on human populations around the world,’ warns IPBES.
3. What are the main pressures on biodiversity, and what are the consequences for humans?
Five major pressures have been identified as responsible for the current decline in biodiversity. Drawing on the conclusions of IPBES (the equivalent of the IPCC for biodiversity), the biologist cites:
- habitat loss (deforestation, urbanisation)
- pollution (soil, ocean, light)
- climate change
- biological invasions
- overexploitation of resources
These pressures interact with each other, exacerbating the effects. For example, pesticides cause both soil pollution and the decline of pollinators. Yet pollinators are essential: ‘more than 80% of pollination in Europe is carried out by wild pollinators,’ Céline points out. Their disappearance would lead to a collapse in agricultural productivity. In some regions, ‘pollination is done by hand,’ particularly for crops such as vanilla. The loss of biodiversity also means the loss of access to medicinal and food resources, as well as ecological regulation.
Céline emphasises that ‘all the services that biodiversity provides to humans could be jeopardised’, thereby threatening food security, human health and the balance of societies.
4. What is the link between biodiversity, climate and other planetary boundaries?
There is a two-way link: ‘climate will determine the distribution of species’ and the dynamics of ecosystems, and, in turn, the health of ecosystems also influences the climate. Céline points out that ‘oceans, forests and peatlands are important carbon storage areas’ and that their degradation weakens their ability to mitigate climate effects. Thus, ‘once biodiversity is degraded, it can no longer fulfil its role as a carbon store’, which exacerbates global warming.
The loss of a natural habitat, such as a forest replaced by bare soil, means that it can no longer play this regulatory role. This can amplify local warming, but also promote phenomena such as soil erosion and flooding. ‘From that point on, we have a chain reaction,’ where the various planetary boundaries—climate, biodiversity, land use—interact and reinforce each other’s disruption.
5. What concrete solutions can be implemented at all levels to halt biodiversity loss?
It is crucial for companies to start by measuring their impact. Although the carbon footprint is now widely quantified, the biodiversity footprint is still emerging. Céline cites two tools: ‘EU Business for Biodiversity’ and ‘Global Biodiversity Score’ developed by CDC Biodiversité, which enable companies to measure their biodiversity footprint. However, she acknowledges that ‘quantifying one’s impact on biodiversity implies quantifying known biodiversity’, yet a huge part of it remains unknown. Despite this uncertainty, she considers measurement to be a fundamental step: ‘it allows us to take stock of our role and set impact reduction targets’.
The response to the biodiversity crisis then relies on coordinated action at several levels, from governments to citizens. At the national level, the scientist stresses the importance of ‘establishing strict protected areas’ to maintain undisturbed habitats.
Local authorities can limit habitat fragmentation through controlled urbanisation and the preservation of natural spaces in cities. At the individual level, actions such as ‘not concreting over your garden, planting wild flowers and preserving hedges between crops’ encourage the return of diverse wildlife.
In terms of consumption, she calls for ‘eating less meat, consuming locally, and favouring organic farming’. These choices reduce the use of pesticides, which is beneficial for our health, biodiversity and soil fertility. Céline also emphasises the ability of biodiversity to help us adapt: ‘Ecosystems are capable of being resilient to stress,’ provided they are diverse. This diversity is essential because ‘several species can fulfil the same function and replace a species that has disappeared.’ In short, diversity is the key to resilience. She concludes with a strong message: ‘We can all contribute to limiting human impact on biodiversity.’
Céline Bellard is a biologist and researcher at the CNRS, currently attached to the Ecology, Systematics and Evolution Laboratory at Paris-Saclay University. Supported by the AXA Research Fund, she specialises in the study of biodiversity, particularly biological invasions and ecosystem vulnerability. She has conducted postdoctoral research at University College London and is now dedicated to research in conservation biology, with a focus on biodiversity loss and species extinction. In addition to her scientific work, Céline is involved in popularising science and promoting women in science through the L’Oréal Foundation’s Girls in Science programme. In 2022, she received the Irène Joliot-Curie Prize – Special Prize for Commitment.
