Every two years, the World Wildlife Fund (WWF) assesses the abundance of wild vertebrate populations, through its “Living Planet Index” (LPI). And, every two years, this indicator describes a decline that increases, inexorably. According to the latest edition of the report, published Thursday, October 13, populations of birds, fish, mammals, amphibians and reptiles have declined by an average of 69% between 1970 and 2018. In 2020, the same indicator showed a drop of 68%.
“A drop of 1% in two years is colossal, and we have lost 10 points in ten years, underlines Arnaud Gauffier, the program director of the WWF. On very low populations, this can be dramatic and lead to extinctions. The mere fact that this indicator is not improving is catastrophic. » Vertebrates represent less than 5% of known animal species, but are the most followed.
Great disparities
In just fifty years, according to the LPI, lowland gorilla populations have declined by 80%; those of Africa’s forest elephants, listed as critically endangered, by 86%. The populations of oceanic sharks and rays have also collapsed (–71%). Other populations – about half of those studied – are stable or increasing.
Developed by the Zoological Society of London, the Living Planet Index calculates an average evolutionary trend for tens of thousands of populations of terrestrial, marine and freshwater vertebrates. This year, 31,821 populations representing 5,230 species were taken into account, representing 838 new species and 11,011 more populations compared to 2020 – a considerable increase. The number of species of fish (+29%) and birds (+95%) in particular, as well as data from previously underrepresented regions, such as Latin America and the Caribbean, have been greatly expanded.
At the end of 2020, researchers had judged, in an article published in Sciencethat this indicator gave a vision “catastrophist” of the erosion of biodiversity, estimating that the extreme reduction of certain populations affected in a way “disproportionate” the overall average. For this new edition, the LPI has been recalculated by excluding certain species or populations. “This confirmed that the index was not driven by extreme declines or increases”write the authors of the report.
The loss of biodiversity is particularly complicated to summarize in a figure or a measurement that would create consensus, the phenomenon being multidimensional. “The GPI allows useful comparisons to be made from year to year and to give an order of magnitude of the loss of biodiversity, explains Michel Loreau, research director at the CNRS. But I prefer other more specialized and homogeneous studies on the decline of birds or insects, which are just as alarming. »
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