Endangered species of animals and their characteristics. Scientific library - abstracts - causes of extinction of animals and plants in the past and present. Variety of marine life
You know that the development of living nature, as a rule, follows the path of increasing complexity of organization. Why do some species become extinct and are replaced by others?
The main directions of the evolutionary process are biological progress and regression. These directions were identified by A.N. Severtsov and I.I. Shmalgauzen.
Biological progress is characterized by an increase in the number of individuals of a systematic group, an increase in the number of species, subspecies, and populations included in it, and an expansion of the range. Species in a state of biological progress emerge victorious in the struggle for existence.
What do trilobites and dinosaurs have in common? They ended in mass extinction. 185 million years passed, but neither was able to escape the great catastrophes that broke the earth. Mass extinction is a global catastrophe. More than half of all known animal and plant species have been extinguished. This has happened five times in the last 540 million years. At one point, 250 million years ago, it was so bad that the earth was almost relegated to the microbial stage. Geologists debate the causes of these great stereobooks, giant volcanic eruptions called or asteroid attacks, to lead only the two most famous theories.
Biological progress can be achieved through aromorphoses, idioadaptations or degeneration. For example, the biological progress of angiosperms was facilitated by aromorphoses - the appearance of a flower and a fruit, which led to a significant improvement in the processes of pollination, fertilization, formation and distribution of seeds, and plant reproduction in general.
The worst disaster on Earth
Climate always seems to play a role, or better yet, climate change. With current climate change, scientists therefore fear that humans have already caused the sixth mass extinction. Their death is as inevitable as that of humans. More than 99 percent of all species that have ever existed have gone extinct over a long period of time. It is quite normal for such “background noise” to die. But from time to time, everything that happened in the history of the Earth stood on a knife's edge, and life slid into deep crises.
The concept of “endangered organism”, a general description of the causes of extinction of animals and plants
The mass extinction took its course, and many species disappeared at once. These are eras of interruption and upheaval in which the book of life is rewritten. Mass extinction is a decisive step in the development of life - and not just in a negative sense. They can extinguish dominant organisms and send evolution in a new direction.
The further evolution of angiosperms followed the path of idioadaptations, the emergence of various adaptations to different living conditions. Idioadaptations led to the appearance of plants with different flowers, fruits, shoots, leaves, root systems, development periods, adaptations to pollination by wind, water, and insects. Thanks to idioadaptations, a large number of species of angiosperms have emerged.
Three hypotheses about the causes of extinction will be considered below.
Massive volcanic eruptions infinitely more powerful than Mount St. Helens are blamed for the mass extinction. The reason: In a short time, many species disappear in mass extinctions, and groups that dominate ecosystems and prevent other people from doing so are quite disappointing. This opens up new opportunities for survivors. However, the differences between before and after don't always have to be dramatic. Neither the catastrophe at the end nor in or brought about a new era. New developments have appeared, but there is no revolution.
Biological regression is a direction of evolution that is characterized by a decrease in the number of species, subspecies, populations, and a reduction in range. Biological regression has affected many species of amphibians and ferns. The end result of regression is the extinction of the species.
The cause of biological regression is often human activity. Humans influence species directly, by destroying them, or indirectly, by changing their habitat. So, at the beginning of the 17th century. - wild bulls - aurochs - were exterminated. By the second half of the 18th century. were completely destroyed marine mammals- Steller's cows. By the beginning of the 19th century. hunters completely exterminated the large flightless moa birds that lived in the forests of New Zealand, reaching three meters in height.
The cuts were more like a flesh wound that healed quickly. Finally, the evidence contradicted anyone other than Charles Darwin. According to him, evolution must continue unabated, resulting from the struggle for scarce resources. It was constant change, no breaks. But Darwin was wrong: evolution knows deep distortions. This is not slow competition between species. In contrast, in these mass extinctions, the environment seems to change so quickly that many creatures are unable to adapt and go extinct.
The Ice Age triggered extinction
But what can cause such upheaval? How strong is the destruction to resist life? The oldest crisis we have found in rocks occurred 600 million years ago, when microbial moths and bacterial cones caused serious burglaries due to the introduction of burrowing animals from which they never recovered. But because we know little about the world since then, the consequences cannot be assessed, and this "incident" remains unchanged when counting mass extinctions.
There are other reasons for the extinction of species. The evolution of species is determined by the interaction of natural selection and the characteristics of the biological organization of species. However, the possibilities for evolutionary changes in a species are not unlimited; there are evolutionary restrictions. For example, each species is characterized by a certain spectrum of mutations. Some mutations are impossible due to the lack of genetic prerequisites. Thus, in fly drosophila mutations are impossible that would determine the appearance of individuals with green or blue eyes.
The first "regular" mass extinction occurred about 440 million years ago. In Ordovicca, 60 to 80 percent of all known species have disappeared from the sea. The second mass extinction occurred 367 million years ago in Devonian. At the time, the mass extinction appears to have captured mariners in several attacks. The worst catastrophe occurred about 251 million years ago, when more than 90 percent of all species known to us perished, more than 70 percent of terrestrial species. The world as it existed before is gone.
The next crisis began about 210 million years ago, and it was difficult to live life both in the sea and on land. At that time, the Saurs took control of the earth - 65 million years ago, another world, the center of the Earth, ended, and the last of them had to abandon them. They disappeared, except for those who turned into birds.
Sometimes the most successful adaptation that promotes progress becomes the cause of evolutionary limitations at a certain stage of development. For example, the appearance of tracheas (air breathing organs) in insects gave them ample opportunities for mastering the air habitat. However, with the appearance of tracheas in insects, the circulatory system became more simply structured, as a result, the supply of nutrients to the organs deteriorated, which led to a decrease in body size. The largest extinct dragonflies reached a length of 75 cm, and the largest modern insects do not exceed 12-15 cm.
Our earlier ideas about these events came from the "refilling" of abandoned niches, such as a chessboard from which a mass extinction simply destroyed the pieces, and then the board was filled by the creation of new pieces, explains Doug Erwin of the Smithsonian Museum of Natural History in Washington. DC, but the checkerboard rooms were preserved, they were, so to speak, a legacy of the old ecosystem before the mass extinction, which is not true, because then the niches would have to survive Reality with the species that lived in them.
Thus, limiting factors limit the possibilities for further evolutionary changes and often lead to biological regression.
EXTINCTION OF SPECIES, a phenomenon that occurs in the process of development of living nature throughout geological history. history of the Earth. Occurs as a result of nature. selection, conditioned both by significant changes in the external environment, to which certain organisms do not have time to adapt, and by minor changes in living conditions, leading to a delay in the reproduction of any species. V. in. plays an important role in the evolution of living nature. It is known that many forms of plants and animals have disappeared. According to the teachings of C. Darwin, V. century. occurs when environmental conditions change due to the enormous influence of changed external factors, be they abiotic, related to the inorganic world (for example, chemical composition soil or atmosphere, fresh and sea waters, air temperature, radiation regime, etc.), or biotic, relating to interspecific relationships (the mutual influence of living organisms of different species on each other), including anthropogenic factors arising under the influence of human activity and steady growth population. If species occupy a limited area or water area, then the immediate cause of their extinction may be rapid changes in the habitat. Widely distributed species that live simultaneously on most continents or in all oceans do not disappear everywhere, and the final extinction of some species is often delayed due to local favorable conditions, usually biotic. This explains the existence of relict forms (i.e., preserved as a remnant of bygone eras of the distant past), which include modern American species of grapes of the genus Vitis that survived the Tertiary period. According to paleontologists. According to data, many genera and species of grapes became extinct during the change in geological conditions. eras. Some were found in archaeological sites. excavations and described. Extinct species of grapes include, for example, Cissites parvifolius, previously described by Fontaine under the name. Vitiphyllum and later assigned to the genus Cissites; found in the Lower Cretaceous deposits of the east. parts of the North America, in the West Europe, as well as near Lake Chushka-Kul in Kazakhstan. This species has had many forms with a large range. Extinct species of the genus Vitis include fossil species V. dakotana, V. Leei, V. arctica, V. sachalinensis, V. teutonica, V. praevinifera, V. Ludwigii, etc. In the territory. CIS (Middle Asia, Urals, etc.) species Cissites Kryshtofovichianus, C. uralensis, etc. were also found in the Upper Cretaceous deposits. Some species of the genera Cissus and Tetrastigma are also known in the fossil state (see Family Vitaceae Juss).
After a mass extinction, ecosystems are “minimalistic.” When a disaster occurs, food chains and habitats disappear. Those who are still surviving suddenly did not compete. Species that previously existed modestly on the margins multiplied explosively. Opportunists take the helm. But these creatures are often genetically determined. They are perfectly adapted to poor conditions, but do not have the opportunity to develop further. They form a system for transition. At some point, the situation returns to normal again, life returns.
According to Doug Erwin: Many new species suddenly appear, others reappear that seem to have disappeared, but they probably survived the extinction and time later in the niche - Dachshund, because they seem to come back from the dead if they appear after millennia. Life is exciting again.
Lit.: Davigashvili L. Sh. Causes of extinction of organisms. - Moscow,
1969.