The rate of biodiversity loss is growing

    22 Jul 2021

    Throughout the history of the Earth, there have been several mass extinctions of animals. But humanity has turned the last of them into a process of unprecedented scale.

    Let’s check the zoologist, Ph.D. on zoology Vilaly Gryshchenko’s opinion about it.

    Throughout the existence of the Earth’s biosphere, some species of living beings have appeared, others have disappeared. Their extinction was constant, it is an entirely natural process, but the emergence of new species balanced it. However, there have been crises where biodiversity has declined sharply.

    Paleontologists had described five mass extinctions in the last 540 million years when three-quarters or more of the species that existed on the planet disappeared. This is considered primarily global catastrophic processes – climate change, sea-level fluctuations, movement of continents, volcanism, etc. Currently, the most significant global cataclysm is human activity. Humans have directly or indirectly been the cause of the extinction of many species of animals and plants on Earth. One of the founders of geochemistry, biogeochemistry, and radiogeology, Vladimir Vernadsky, also wrote that humanity had become a geological force on a planetary scale. And the impact of this force on biodiversity is negative.

    Scientists have talked about the sixth (Holocene) mass extinction (there’s Elizabeth Colbert’s book about it). It covers the entire Holocene (modern geological epoch, which began 12 thousand years ago) and gained momentum. And although in terms of the total number of extinct species, this extinction is far from the Big Five, the speed of this process is much higher than natural.

    But these are all words, and is it possible to quantify the damage to nature somehow and prove that the culprits are people and not, say, climate change or geological processes? To do this, we must compare how extinction occurred before and after the appearance of humans and determine the impact on him of various factors.

    This is exactly what a group of European scientists, Tobias Andermann and his colleagues did. They used computer simulations to analyze the extinction of mammals on Earth since the late Pleistocene (previous geological epoch, 2.6 million 12,000 years ago; the late Pleistocene began 126,000 years ago). The results of their research are published in one of the most prestigious scientific journals in the world – Science Advances.

    There are now about 5,700 species of mammals on Earth. Another 351 species have disappeared since the late Pleistocene, 80 of them in historical times, after 1500 AD. Scientists have noticed similar trends among other classes of vertebrates: birds, reptiles, amphibians, bony fish. All this gives grounds to speak of the sixth mass extinction.

    The authors of the study took from the scientific literature information about the latest findings of each of the 351 species of extinct mammals – dating fossils for those that disappeared long ago or observations for species that became extinct after 1500. The 126,000-year period includes both significant climate change (Pleistocene glaciation, interglacial, Holocene warming) and human settlement on the planet. The simulation made it possible to assess the impact of each of these factors on mammalian extinction. It showed that the current extinction rate is about 1700 times higher than it was at the beginning of the Upper Pleistocene. Extinct species could exist for an average of about 1.75 million years at a constant rate of extinction and only 810 years – at present.

    Scientists have identified four periods of the significant increase in the extinction rate of mammals: 63.8-32.2 thousand years ago, 16.0-9.5 thousand years ago, 2300-600 years ago, 180-120 years ago. They are in good agreement with the stages of human colonization of new continents and islands. Thus, in the first period was inhabited by Australia, in the second – America. But a coincidence in time does not necessarily mean a causal relationship. The answer was given by further modeling. Factors related to people (population and area) and climate (global temperature and rate of change) were taken into account. It turned out that the population explains the extinction of mammals with an accuracy of 96.0%, populated area – 97.1%. But the influence of climatic factors is much lower – 63.6% – for temperature and 60.2% – for the rate of change. In addition, these indicators do not differ statistically significantly from similar parameters for the “zero” model – the calculation of events provided that the rate of extinction remains unchanged all the time. That is, in general, climatic factors played a minor role in this case. Mixed models that considered the combined influence of humans and climate also showed a significant predominance of anthropogenic factors.

    Scientists have long noticed that after people populated new areas, their biodiversity declined sharply. Large animals and birds (the so-called megafauna) suffered the most, which were first hunted or which disturbed the settlers the most (you can read more about this in another article for Kunsht). The results of Andermann’s study with co-authors once again confirm this. It was after the advent of humans that the rate of mammal extinction increased sharply. And that’s where wild animals and people last time evolved together; such a catastrophe did not happen.

    The animals managed to adapt to the “super predator” and were not defenseless against him. In Africa, the extinction rate did not increase at all, and the loss of diversity was relatively slow. In Eurasia, the pace of these processes was slower than on other continents. The most incredible devastation was experienced by island territories (data from Madagascar and the Caribbean). The simulation also shows the different vulnerabilities of different systematic groups of mammals. A number of the proboscis (megafauna!) were almost completely exterminated, but primates suffered much more minor.

    The forecast of the authors of the article, unfortunately, is disappointing. If the rate of extinction remains constant, by 2100, about 30 more species of mammals will disappear. If it continues to overgrow, this fate can expect 558 species.

    Of course, such modeling involves simplification – the influence of only certain factors is analyzed. In nature, this does not happen; each species is affected by a range of factors. And they can both strengthen and weaken each other. But the main conclusion is still indisputable – humanity itself is primarily responsible for the sixth mass extinction, the tragedy unfolding before our eyes.

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