Diversity of life on Earth has not changed since the days of the dinosaurs
A rich variety on land that we see today around the globe - the phenomenon is not new: the diversity of life on the land has not changed in at least the last 60 million years ago. Recall that the dinosaurs became extinct about 65 million years ago. According to a new study conducted by researchers at the University of Birmingham, the number of species in ecological communities on land increased only sporadically in the course of geological time. The rapid growth of diversity followed by a plateau that lasted for tens of millions of years.
How many species on Earth?
Previously, many scientists have argued that diversity is steadily increasing with the passage of geological time, which would mean that biodiversity is much greater today than it was tens of millions of years ago. But to create an accurate picture of how there was a diversity of life on land, it is very difficult, because the fossil data are becoming increasingly scarce, the farther back in time we go. Using modern computer technology, capable of analyzing hundreds of thousands of fossils, we begin to see patterns that challenge this view.
Researchers from the School of Geography, Earth Science and Environment at the University of Birmingham and other institutions in the UK, US and Australia were able to study the details of fossils collected by paleontologists for the last 200 years of the 30 000 different excavations around the world. The scientists took as a basis the data on terrestrial vertebrates, which allow for the earliest appearance of this group of almost 400 million years ago. It was found that the average number of species did not increase for tens of millions of years in the environmental community of terrestrial vertebrates. The results, published in the journal Nature Ecology & Evolution, show that the interaction between species, including competition for food and space, limits the total number of species that can coexist.
Lead researcher Dr Roger Klose said: "Scientists often assume that the diversity of species in an uncontrolled increase in the course of millions of years, and that the diversity of today is much more than in the past. Our research shows that the number of species within terrestrial communities is limited for long periods of time, which is contrary to the result of many experiments in modern ecological communities - and now we need to understand why. "
One of the reasons why the diversity in ecological communities is not increased, it may be that the resources used by the species, such as food and space is limited. Competition for these resources can prevent the penetration of new species in the ecosystem and lead to a balance between the rates of speciation and extinction. However, after the appearance of the major animal groups, or major environmental disturbances, such as mass extinctions, increasing diversity can happen suddenly - in geological, and not by human standards - and behind them again followed by long periods without any increase. "Contrary to expectations, the greatest increase in diversity in the communities of terrestrial vertebrates occurred after the mass extinction that killed the dinosaurs 66 million years ago, during the late Cretaceous period. In just a few million years of local diversity has increased two to three times compared to the level before extinction - mainly due to the impressive success of modern mammals. "
Professor Richard Butler, who also was a member of the research team, adds that if you understand how to change the diversity in the past, we have been able to better understand the possible long-term effects of the current biodiversity crisis.
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