When biodiversity falls below the vital minimum

Jean-Luc Goudet
Journalist

The collapse of wild animal populations affects the entire planet: this is what the 550 scientists for the IPBES , a sort of IPCC of biodiversity, who wrote their report submitted this March 23, 2018. The endangered species of disappearance sometimes make the headlines, but it is an equally important notion: what is the minimum size of a population below which a species is irremediably doomed to disappear? In 2016, a large British study of nearly 40,000 species answered the question. Moreover, it concluded that, on more than half of the Earth's land, biodiversity has fallen below this limit value.

Article published on July 25, 2016

Biodiversity losses are today often quite well documented in different environments. Between agriculture and urbanization, the disappearance of species , locally or globally, is undeniable. But is it serious? For the first time at this scale and with this precision, scientists, led by Tim Newbold of UCL ( University College London ), took stock of the evolution of the number of species of terrestrial ecosystems .

The researchers worked on 2.38 million data, concerning 39,123 species, collected on 18,659 sites by hundreds of scientists collaborating in the project Predicts ( Projecting Responses of Ecological Diversity in Changing Terrestrial Systems ). This patient count led to an estimate of biodiversity up to a unit area of 1 km 2 .

The result, described in the journal Science , quantifies the decline by " biome ", that is to say by type of environment (meadow, desert , temperate forest ...), by comparing with the number of species " "original", that is, before human activities have changed the habitat. The authors considered a limit, a "threshold of sensitivity", below which equilibrium is no longer possible. This concept had already been mentioned in earlier work on " planetary boundaries ". In 2009, researchers had identified areas where human activities could exceed the planet's resilience . From biodiversity to the use of fresh water, climate and the cycles of nitrogen and phosphorus , the study pointed to nine. In 2014, another team claimed that four of these borders had been crossed or would soon be crossed.

In red, the regions where the loss of biodiversity exceeds the limit considered as the threshold of sensitivity. In yellow, those where she approaches. In blue, regions where biodiversity is good. © UCL

58.1% of the land under the limit

According to the study by Tim Newbold's team, biodiversity has fallen below this threshold, set at 10%, on 58.1% of the land area. "In these territories live 71.4% of human beings" underline the researchers in the UCL release . The most affected biomes would be grasslands , savannas and bush. It is essentially the exploitation of these surfaces for human activities that make them flee plants and animals. "The biggest changes have occurred where humans are the most numerous," say the researchers.

The consequences of a degradation of these ecosystems - desertification for example - also have a strong impact on the human populations and the researchers conclude by urging the public authorities to preserve, as far as possible, natural environments.

Source: futura-sciences.com
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