Causes and consequences of species decline
Butterflies, birds, bees, fish, orchids – the diversity of animal and plant species has declined sharply in recent years. Over the coming decades, the world risks the further loss of up to one million species globally, warns the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) in its “Global Assessment Report on Biodiversity” of May 2019. This decline not only leads to the loss of benefits for humans – it threatens our global ecosystem. The 2024 Biodiversity Fact Check also highlights the dramatic state of biodiversity in Germany.
What is biodiversity?
Biodiversity has three dimensions: the diversity of species, i.e. all animal, plant, fungal and microorganism species, the genetic diversity within these species and the diversity of ecological communities such as forests, moors, seas, lakes and meadows. It is therefore the basis for functioning ecosystems and human life.
Biodiversity is very unevenly distributed globally. The most species-rich areas of the world are found in the tropics. Species richness decreases from the equator to the poles. The last intact wilderness areas, for example the core zones of the large tropical or boreal forest regions (also known as taiga), often make a significant contribution to ecosystem services and store a third of the carbon that exists on land.
Questions and answers
Question
What are ecosystem services?
Answer
Ecosystem services refer to the benefits that humans derive from natural ecosystems. This refers to all the services that nature and biodiversity provide for human well-being: Supporting services, i.e. basic natural processes such as nutrient cycles or the growth of plants, provisioning services, i.e. the provision of material goods such as food, drinking water or wood, regulating services, i.e. natural functions such as climate regulation, pollination of plants or flood protection, and cultural services, i.e. non-material contributions from nature such as recreation or aesthetics.
The concept of ecosystem services originates from environmental economics and ecology and is now a key concept at the interface of natural and social science environmental research. In more recent international assessment frameworks, particularly in the context of the World Biodiversity Council (IPBES), the approach has been further developed and summarised under the term "Nature's Contributions to People".
Why do we need biodiversity?
Animals, plants, fungi and microorganisms have important functions in the earth's ecosystem. The diversity of species provides food, provides active ingredients for medicines, is used for recreation and plays an important role in climate regulation. Without biodiversity, we could not exist on our planet.
Biodiversity in ecosystems
Many different plants fulfil different tasks in the ecosystem. While some plant species primarily promote biomass and humus formation, others make a particular contribution to the stability of ecosystems. Stable, species-rich ecosystems absorb carbon dioxide by continuously forming biomass. Some of this carbon is stored in the soil as humus or peat via dead plants and roots, where it remains bound in the long term. Ecosystems with high biodiversity are more resistant to change. However, if species are missing, the cycles are disrupted. If insect species die out, for example, this has an impact on birds, among others, which feed on these insects.
Audioplayer
Biologist Prof Dr Katrin Böhning-Gaese on biodiversity in ecosystems
Audio in German | “We know that biodiverse ecosystems are more stable. Let's say we have a drought one year and another where it rains a lot, where it is cold or unusually warm, a meadow with a variety of thirty or forty different species of plants will always have some that cope well with the prevailing conditions. We also know from long-term studies that biodiverse ecosystems are much more reliable in the long term to provide biomass for the harvest.”
Copyright: Peter Kiefer
Biodiversity and nutrition
Insects perform essential work in the pollination of plants and thus for the harvest. The decline in biodiversity is therefore also a threat to human food security. The economic value of these "services" provided by insects, which pollinate three quarters of all crops worldwide, is estimated at around 500 billion dollars a year.
Audioplayer
Landscape ecologist Prof Dr Alexandra-Maria Klein on biodiversity and pollination
Audio in German | “When certain species are missing, less pollination occurs and that means less yield.”
Biodiversity and health
Nature also serves us humans for recreation. In its status report of May 2019, the World Biodiversity Council also emphasises the benefits of nature for human well-being. A diverse natural environment improves mental and physical health, including through the provision of diverse, varied food.
Audioplayer
Agricultural biologist Prof Dr Josef Settele on biodiversity and health
Audio in German | “Health is also about diversity.”
However, the World Biodiversity Council (IPBES) also ascribes an ethical and moral value to biodiversity that goes beyond human interests. Nature and living organisms therefore have a value in themselves and thus a right to exist, even if they have no direct economic or functional benefit.
What losses are there in biodiversity?
Globally, biodiversity is declining dramatically. Only around 20 to 34 per cent of terrestrial ecosystems are little to very little changed by humans. Only around 3 per cent have an intact fauna unaltered by humans. Today, it is assumed that around 1 million of the estimated 8.7 million plant and animal species worldwide are threatened with extinction, many of them in the coming decades. The decline in biodiversity varies around the world, with tropical regions - including savannahs - being particularly badly affected, especially in South America.
In Germany, almost a third of all animal and plant species are considered endangered. The number of flying insects has fallen by at least 75 per cent in the last thirty years and a good two hundred flowering plant species are on the "Red List" of endangered plants in Germany.
Audioplayer
Botanist Prof Dr Thomas Borsch on endangered plant species
Audio in German | “The most famous endangered plant is arnica.”
The loss of biodiversity in Germany is particularly worrying in agricultural landscapes, but even in nature reserves, a sharp decline in species diversity can be observed. The causes lie in a combination of many factors: Species-poor arable crops provide few habitats and food sources for plants and animals; pesticides kill not only pests but also many beneficial insects and other organisms; monocultures crowd out other plant species and thus reduce ecological diversity. Overall, the main problem is a change in land use that is destroying the habitats of animals and plants. And thus also our livelihood.
Biodiversity researcher Katrin Böhning-Gaese on the loss of species in the agricultural landscape
The World Biodiversity Council warns of the incalculable consequences of species loss. This is because there are so-called tipping points in ecosystems at which sudden and irreversible processes can occur. The processes and consequences differ depending on the ecosystem, time horizon and assessment method. Given the complexity of ecosystems and the interaction between species and the environment, these tipping points are difficult to predict.
Audioplayer
Landscape ecologist Prof Dr Alexandra-Maria Klein on tipping points in ecosystems
Audio in German | “We don't know when or how, but something will happen.”
“We don't know when or how, but something will happen.”
Deepening on the subject
- Video: Biodiversity: Impact and change - Lecture Christian Wirth on the report of the World Biodiversity Council IPBES 2019 (German only)
- Discussion paper "How can international agricultural trade contribute to biodiversity conservation, climate protection and food security? Towards coherent governance of consumption, production and trade" (2025, German only), Chapter 3.1 Biodiversity loss
- Digital dossier "15 answers to 15 questions on biodiversity": What losses are we seeing? (German only)
- Statement "Biodiversity and Management of Agricultural Landscapes" (2020): Chapter 2 State and development of biodiversity
What are the causes of the decline in biodiversity?
The five main drivers of species loss are land-use change (e.g. expansion and intensification of agriculture), direct exploitation of species (e.g. hunting, fishing), climate change, pollution and the spread of invasive species.
Land use change
According to the report by the World Biodiversity Council IPBES, the main cause of species decline is changes in land use. These include increasing sealing due to large-scale construction, the loss of structural diversity in the landscape and, above all, ever larger areas of agricultural land, which are associated with the draining of moors, deforestation or the conversion of grasslands and savannahs. In addition, agriculture has become industrialised. Whereas small, varied fields used to be cultivated in the past, today there are predominantly monocultures with high-yielding but species-poor arable land.
Exploitation of species
In the oceans, fishing and hunting activities are causing a severe loss of biodiversity. Industrial fishing has greatly reduced many stocks. Millions of animals die every year due to bycatch, i.e. unwanted catches in nets. Bottom trawls also destroy sensitive seabeds. Hunting and poaching have also minimised numerous populations on land, and some species such as otters and brown hares have even been almost wiped out. Many wild plant species have also been massively removed from ecosystems: for medicinal use, as ornamental plants or timber.
Climate change
As a result of climate change, habitats are becoming uninhabitable for native species, species are becoming locally or regionally extinct or are having to spread to cooler regions. Some species are unable to adapt quickly enough or find suitable new habitats, which jeopardises their survival. For example, the rise in sea temperatures is having a dramatic impact on coral reefs. Excessively warm temperatures cause coral bleaching and thus the death of entire marine ecosystems. Climate change is also altering life cycles, which affects food chains, for example when plants flower too early for pollinating insects or insects hatch too early for young birds.
Environmental pollution
Chemical pollution such as pesticides, air pollution, waste and microplastics have a serious impact on biodiversity. Over-fertilisation, for example, causes fast-growing grasses to spread rapidly and displace other species. Massive algae growth is occurring in the oceans, resulting in oxygen-depleted zones in which only a few species can survive. Litter and microplastics also harm animals, disrupt nutrient cycles and alter habitats. Microplastics are particularly problematic because they can be measured everywhere - in soils, rivers and oceans - and are hardly broken down again.
Spread of invasive species
Invasive species, i.e. alien animal, plant, fungal or microorganism species, are usually introduced into new habitats by humans - intentionally or unintentionally. There they spread rapidly, displacing native species and changing ecosystems. The rabbit, for example, was brought to Australia by Europeans. There it multiplied unchecked and destroyed the native vegetation. In Germany, for example, the American signal crayfish is displacing native crayfish species. Plants can also be invasive, such as the Japanese knotweed, which spreads rapidly and destroys banks and infrastructure through uncontrolled growth.
Deepening the topic
- Digital dossier "15 answers to 15 questions on biodiversity": What are the causes of biodiversity loss? (German only)
- Digital dossier "15 answers to 15 questions on biodiversity": How does climate change affect biodiversity? (German only)
- Statement "Biodiversity and management of agricultural landscapes" (2020): Chapter 4 Causes of the decline in biodiversity in agricultural landscapes (German only)
Leopoldina members on their research
Many Leopoldina members deal with the topics of biodiversity and biodiversity loss in their research. On behalf of the Leopoldina, they are involved in science-based policy advice, within working groups, in the preparation of statements and discussion papers or at events.
- Deep-sea researcher Antje Boetius talks about the mysteries of the deep sea in the video format "3 Minuten Zukunft", a collaboration between the Leopoldina and Mitteldeutscher Rundfunk (German only)
- In his evening lecture on the occasion of the presentation of certificates to new members of Class II - Life Sciences in May 2022, biologist Lars Chittka reported on his research into the intelligence of bees (German only)
- In his keynote speech at the 2021 Leopoldina Annual Assembly, Christian Wirth presented a study on "biodiversity" in culture and literature. (German only)
Published: October 2020, Updated: April 2026