Species extinction


August 15, 2022

In biology and ecology, extinction is the total disappearance of a species or a group of taxa, thus reducing biodiversity. Ecologists distinguish this numerical extinction from functional extinction, which is the reduction in population size of a species such that it leads to the depletion or extinction of other species in the community, which alters the functionality and stability of the ecosystem. Through evolution, new species arise through the process of speciation — where new varieties of organisms emerge and develop when they are able to find and exploit an ecological niche — and species die out when they are not. more able to survive in changing conditions or in the face of competition that they cannot meet. Typically, a species dies out in 5 to 10 million years (excluding periods of biogeological crisis), although some species, called living fossils, survive practically unchanged for hundreds of millions of years, such as the Ginkgoaceae family. , which is around 270 million years old. Only 1/1000 of the species that have existed are still alive today. Paleontological data show that extinction rates were consistently low before human expansion across the planet, and that mass extinctions were rare events. Beginning approximately 100,000 years ago and coinciding with the growth in numbers and distribution of humans, species extinction has increased at a rate unprecedented since the Great Cretaceous Extinction, reaching an extinction rate of 1– 2.2% of species in the last decades of the 20th century (one in 1,000 species every 1,000 years according to the Millennium Ecosystem Assessment). This phenomenon is known as the Holocene extinction and represents the sixth, mass extinction. In the early 2000s, experts estimated that more than half of the then living species could become extinct before 2100. This prediction was challenged by Bjorn Lomborg, but at the end of 2014 a new assessment published in the journal Nature concluded that it remains impossible to precisely quantify all biodiversity, but that for known species the situation is worsening: amphibians are the most threatened (41% of endangered species), ahead of birds (26%) and mammals. 60% of corals could die even before 2050. If we consider the range of a prospective assessment (36,000 species disappearing per year around 2010-2014) the 6th extinction (75% of species would then have disappeared) could occur around 2200 (if nothing more is done to avoid it). To the old and natural causes of extinction (hunting, overexploitation, etc.) have been added recent anthropogenic causes such as the effects of pollution, the overexploitation of natural resources, the destruction of habitats or the insularization induced by the increasing ecological fragmentation of landscapes. These effects could in the near future be exacerbated by the effects of climate change. Since 1900, the disappearance of species has multiplied by 100, a rate unparalleled since the extinction of the dinosaurs. According to the 2019 Global Assessment Report on Biodiversity and Ecosystem Services, published by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, the biomass of wild mammals has declined by 82%, natural ecosystems have lost about half their area and one million species are threatened with extinction, all largely as a result of human actions. 25% of plant and animal species are threatened with extinction.