Biodiversity is the entirety of life on earth – the diversity of genes, organisms and ecosystems.
We know about the existence of around 1.8 million species. As there is no universal definition of “species”, the number slightly varies. Different methods estimate a total number of between 3 and 100 million species.
Biodiversity distribution on planet earth is uneven. Diversity depends on various factors such as climate, nutrient availability, geography and disturbance. Anthropogenic activities are able to manipulate every single of these factors.
This is exactly what happens as a by-product of modern homo sapiens history: Population growth and increasing abilities to shape planet earth put pressure on ecosystems and biodiversity.
Drivers of modern biodiversity decline include habitat loss, fragmentation and degradation, climate warming, eutrophication, invasive species, light pollution and overhunting.
Ecosystem services are benefits that humanity derives from the existence of biodiversity. These services may be grouped into three categories: Provisioning services (e.g. the provision of clean water, food or timber), regulating services (the maintenance of life-supporting conditions, e.g. climate regulation) and cultural services (e.g. eco-tourism or spiritual experiences).
It is well-studied that higher biodiversity correlates with the functioning of ecosystem services (“ecosystem functioning”). The shape of this correlation remains uncertain. Specific keystone species may have an especially high importance for ecosystem functioning.
Extinction of species always happened. More than 99 percent of the species that have existed during planet earth history already went extinct.
There have been five mass extinction events that each wiped out at least 60-80 percent of species. The most recent mass extinction event happened around 65 million years ago. Causes of mass extinctions may have been fast-paced climate changes, ocean acidification, volcanic activity and asteroids.
The biodiversity crisis of the 21th century is sometimes described as sixth mass extinction. The 2019 IPBES special report estimated that modern extinction rates are 100-1000 times higher than the average of the past 10 million years and that around 1 million species are threatened by extinction. These numbers are extremely high, but nevertheless not at the level of the five mass extinction events.
Conservation refers to the safeguarding of biodiversity, for example by restoring ecosystems, linking fragmented habitat patches or reducing greenhouse gas emissions.
Conservation measures may be justified by the importance of ecosystem services and/or the intrinsic value of biodiversity. The second argument is contested and subject of 20th and 21st century ethics.
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