The study shows that terrestrial diversity is not greater than before

The rich levels of terrestrial biodiversity observed around the world are not a recent phenomenon: terrestrial diversity has been similar for at least 60 million years, and this soon after the dinosaurs' extinction.

According to a new study conducted by researchers at the University of Birmingham and involving an international team of collaborators, the number of species living in ecological communities on Earth increases only sporadically with geological time, a rapid increase in Diversity being followed by trays of tens of millions of years.

Previously, many scientists have argued that diversity increases steadily with geological time, which would mean that biodiversity today is far greater than it was there are several dozens of millions of years. However, it is difficult to draw a precise picture of how land diversity has been assembled, since the fossil record generally becomes less complete later in time. By using modern computer techniques, able to analyze hundreds of thousands of fossils, patterns are beginning to emerge that challenge this vision.

Researchers from the School of Geography, Earth Sciences and the Environment of the University of Birmingham and other institutions of the United Kingdom, the United States and the United States. Australia has been able to study fossil data collected by paleontologists over the past 200 years from about 30,000 fossil sites around the world. . The team focused on terrestrial vertebrate data dating back to the very first appearance of this group nearly 400 million years ago.

They found that the average number of species in ecological communities of terrestrial vertebrates has not increased for tens of millions of years. Their results, published in Nature Ecology & Evolution, suggest that interactions between species, including competition for food and space, will limit the total number of species that can coexist.

Roger Close, Senior Researcher, said, "Scientists often think that species diversity has not been controlled for millions of years, and that diversity is much greater now than in the past. It has been in the distant past.Our research shows that the number of terrestrial species communities are limited over long periods, contradicting the results of many experiments conducted in modern ecological communities – we must now understand why. "

One of the reasons why diversity within ecological communities does not increase in an uncontrolled way over long periods of time can be explained by the fact that the resources used by species, such as food and the space, are finished. Competition for these resources can prevent new species from invading ecosystems and leading to a balance between speciation and extinction rates. After the origins of large animal groups or large-scale ecological disturbances such as massive extinctions, increased diversity can occur abruptly – on geological or even human time scales – and is followed by long periods of time d & # 39; inactivity.

He adds: "Contrary to what one might think, the greatest diversity of terrestrial vertebrate communities occurred after the massive extinction that wiped out the dinosaurs, there are 66 million of them." At the end of the Cretaceous period, a few million years later, local diversity had increased two or three times pre-extinction levels, mainly because of the mammal's spectacular success. modern. "

Professor Richard Butler, who was also part of the research team, said, "Our work provides an example of the combined power of fossil recordings and modern statistical approaches to answer the big questions about the origins of biodiversity. By understanding how biodiversity has changed we may be able to better understand the likely long-term impact of the current biodiversity crisis. "

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More information:
Dynamics of phanerozoic terrestrial tetrapod diversity at the local community level, Nature Ecology & Evolution (2019). DOI: 10.1038 / s41559-019-0811-8