The study by Gerardo Ceballos, Paul R. Ehrlich and Rodolfo Dirzo, published in the scientific journal Proceedings of the National Academy of Sciences, is chilling. They do not hesitate to evoke a “defaunation”, or worse, the alarming acceleration of “the sixth mass extinction”. And this is not a natural phenomenon.
27,600 species on 5 continents
This is what they call “biological annihilation”. In a very alarming study, published in the Proceedings of the National Academy of Sciences (PNAS), American and Mexican researchers conclude that vertebrate species are receding massively on Earth, both in numbers of animals and in extent. A “defaunation” with “catastrophic” consequences for ecosystems and major ecological, economic and social impacts.
The 32% decline in terrestrial animal populations
The three authors, Gerardo Ceballos (National Autonomous University of Mexico), Paul Ehrlich and Rodolfo Dirzo (Stanford) are not at their first test on the theme of the erosion of biodiversity. In June 2015, the first two had already published another study in the journal Science Advances, which showed that the Earth’s fauna was already undergoing its sixth mass extinction. They calculated that species extinctions have increased 100-fold since 1900, an unprecedented rate since the extinction of the dinosaurs 66 million years ago.
Disappearance of populations
This time, the researchers sought to quantify the decline not in the number of species but in populations, that is groups of animals in a territory. “The emphasis on species extinction may give the impression that terrestrial biodiversity is not dramatically and immediately threatened, but that it is just slowly entering a major erosion episode that can be combated. later, “explain the authors.
This approach has several shortcomings in their eyes: public opinion struggles to measure the severity of the phenomenon at work (two species disappear each year, which seems weak, especially when the latter are little known or little used). And it does not correctly assess the current problem. The most common species (whose populations are widely present) are experiencing massive declines in their numbers, without yet being threatened. “The disappearance of populations is a prelude to that of species, warn scientists. A detailed analysis of the declining numbers of animals makes the problem much clearer and worrisome. “
The researchers then conducted an extensive analysis of half of the known vertebrate species: they examined the evolution of the populations of 27,600 species of terrestrial mammals, birds, reptiles and amphibians spread over the five continents, using the The International Union for the Conservation of Nature (IUCN) red list data is the most comprehensive global inventory of the state of conservation of biodiversity. They also looked at the magnesia, more specifically, 177 species of mammals, for which they had data on the range between 1900 and 2015.
“The real scale of mass extinction that affects wildlife has been underestimated: it is catastrophic,” they say. In total, 32% of the species studied decline in population and extent. Many mammals that were doing well a decade or two ago are now endangered.
In 2016, the planet had only 7,000 cheetahs and 35,000 African lions (-43% since 1993). Orangutan populations in Borneo have fallen by 25% over the last decade to 80,000, while giraffe populations have increased from 115,000 in 1985 to 97,000 in 2015. Pangolin populations have been decimated .
30% of declining species are common
What is less well known is that about 30% of these declining species are considered common. They are (still) classified as “low concern” and not “endangered” by IUCN. In France, the goldfinch has, for example, recorded a 40% decline in its numbers over the past ten years. “That as many common species see their numbers decrease is a strong sign of the severity of the current episode of biological extinction,” Gerardo Ceballos warns.
All continents are concerned by this spectacular erosion of biodiversity. The most affected areas, especially for mammals and birds, are those located in the tropics (Amazon, Congo Basin, Southeast Asia) because they are the richest in terms of fauna. But temperate regions have similar or higher rates in relative value – that is, compared to the richness of their biodiversity.
Corollary of the loss of numbers, the wildlife sees its territory diminishing like a skin of sorrows. Of the 177 mammal species surveyed more specifically by the study, almost all have lost at least 30% of their historical range since 1900 and 40% have lost more than 80%. An emblematic case, the lion has long reigned over most of Africa, from southern Europe and the Middle East, to northwestern India; there are only a handful of scattered populations in sub-Saharan Africa and a population in the Gir Forest in India.
Orangutan populations in Borneo, Indonesia, have fallen by 25% over the last decade to 80,000 individuals. BINSAR BAKKARA / AP
In total, more than 50% of animals have disappeared for forty years, say scientists, describing their results as “cautious”. Findings that confirm those of the latest Living Planet report, published in October 2016 by the World Wide Fund for Nature (WWF): he estimated that vertebrate populations dropped by 58% between 1970 and 2012. The interest of the The new study, published in the PNAS, is based on the much larger dataset (27,600 species examined versus 3,700 for WWF) and geographic analysis.
Two or three decades to act
“The approach of this study is very interesting: instead of focusing on extinctions, which are difficult to quantify, it focuses on the evolution of populations, which confirms and provides information on the seriousness of the situation. Judge Benoît Fontaine, conservation biologist at the National Museum of Natural History, who did not participate in the study.
“This publication shows that the situation is very alarming, more than what can be seen in our red list”, abounds Florian Kirchner, in charge of the “species” program for the French branch of IUCN, which only issues a reserve : have focused the analysis on the only terrestrial vertebrates – the most studied – and not fish, invertebrates and plants, whose populations are also declining massively. According to IUCN, 42% of terrestrial invertebrate species (butterflies, earthworms, etc.) and 25% of marine invertebrate species (such as bivalves or sponges) are threatened with extinction.
The causes of these setbacks are known: they are attributable, in the first place, to the loss and degradation of the habitat under the effect of agriculture, logging, urbanization or urbanization. mineral extraction. Then there is overexploitation of species (hunting, fishing, poaching), pollution, invasive species, diseases and, more recently, climate change. “The ultimate drivers of the sixth mass extinction are less often cited, say the authors. It is about human overpopulation, linked to a continuous growth of the population, and overconsumption, especially by the rich. “
“We only have a small window to act, two or three decades at most,” they warn. So is the survival of biodiversity, but also of humanity. “The erosion of species has serious cascading consequences for all ecosystems, as well as economic and social impacts for humans,” says Gerardo Ceballos. The fauna and flora provide us with many services, be it pollination, the improvement of the productivity of the land, the cleansing of the air and the water or the storage of the CO2.
Among the priority actions, scientists call to reduce the growth of the human population and its consumption, to use less destructive technologies for the environment, to stop the trade of endangered species or to help developing countries to maintain natural habitats and protect their biodiversity.