Vom Menschen verursacht: Massenaussterben kann ganze Gattungen auslöschen

Ausgestorbene Wandertaube (Bild von 2014): Nur noch im Museum

Ausgestorbene Wandertaube (Bild von 2014): Nur noch im Museum

Foto: Susan Walsh/ AP

The human race poses a threat to the environment in which it resides. Current situation: the sixth mass extinction in Earth’s history, as researchers call it. It is triggered by humans and the changes they leave behind on the planet. Two scientists now demonstrate that the crisis could potentially be even more profound. They state in the scientific journal „Proceedings of the National Academy of Sciences“ that not only species are becoming extinct, but entire genera as well.

Gerardo Ceballos from the National Autonomous University of Mexico and Paul Ehrlich from the Stanford School of Humanities and Sciences refer to the disappearance of entire species as „mutilation of the tree of life“. They were able to assess extinction at the genus level thanks to improved information on the conservation status of species collected in databases. The researchers examined 5,400 genera of terrestrial vertebrates, comprising 34,600 species.

The result: 73 species of land-dwelling vertebrates have become extinct since 1500 AD. Birds suffered the greatest losses with 44 extinct species, followed by mammals, amphibians, and reptiles. Based on the historical extinction rate of mammals, the current rate of vertebrate species extinction is 35 times higher than that of the past million years, according to the authors. Without human influence, the Earth would have likely only lost two species during this time. However, things turned out differently: in just five centuries, humans triggered a wave of species extinction that would have otherwise taken 18,000 years to occur.

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It is significant because the extinction of genera is more serious than the extinction of species. According to Ceballos, other species from the same genus can take on parts of the role in the ecosystem, thus preserving evolutionary potential. He explains it metaphorically: if a single branch is removed, neighboring branches can intertwine and fill the gap. However, if entire branches are lost, a hole remains in the canopy. It could take dozens of millions of years for it to be closed. According to Ceballos, humanity cannot wait that long for their life support systems to recover, as the stability of our civilization depends greatly on the contributions made by Earth’s biodiversity.

The researchers demonstrate the significance of the disappearance of a species for humans through the spread of Lyme disease. The disease is transmitted by white-footed mice, which used to compete with migratory pigeons for food. With the disappearance of pigeons and the decline of predators like wolves and pumas, mouse populations have increased – along with the cases of Lyme disease in humans.

The loss of species could also exacerbate the climate crisis even further. „Climate disruptions accelerate extinction, and extinction is interconnected with climate because the type of plants, animals, and microorganisms on the planet is one of the most important determinants of the climate we have,“ Ehrlich said according to the statement. The scientists are calling for immediate countermeasures and a greater public awareness of the species extinction crisis.