“Extinction is the rule. Survival is the exception!”
By John J. Hidore
May 19, 2018—-Changes in climate can and do result in the elimination of species of plants and animals. Evolutionary adaptation and ecological equilibrium may not take place as rapidly as the climate changes. Adaptation by plant and animal species to environmental change may take years, centuries or thousands of years.
Different species respond at different rates and in different forms to climate change. Plants are always producing hybrids and individuals with mutations. In any plant species, there are those individuals better suited to the extremes of the range of the plant. These individuals may thrive under changing conditions while the majority perish. In this manner, the optimum conditions for the species changes to those of the new environment. Animals may also come under more and more stress with changing environmental condition and some species become extinct.
The Paleozoic/Mesozoic Mass Extinction
At intervals through geologic time, events have taken place that resulted in the demise of many if not most living species. Extreme cases are called extinctions or mass extinctions. A current definition of a mass extinction is a widespread and unusually rapid decrease in the number of species of plants or animals. There have been at least 13 mass extinctions since life became abundant on the planet. As a result of these mass extinctions 99 percent of all species that have existed on the planet no longer exist.
The most extensive mass extinction of all time happened at the boundary between the Paleozoic and Mesozoic Eras. Ninety percent of all living species died out and very drastic changes took place in the fauna of the planet with a major collapse of marine fauna, especially those living in shallow water on the continental shelves.
Among the organisms that perished were the trilobites. Trilobites were one of the dominant organisms of the seas. They survived the previous two extinctions but couldn’t withstand the changes that mark this period in earth’s history. While many land species disappeared, there was no parallel to the mass extinction of marine animals. The changes were so drastic that the life of the following Mesozoic Era was quite different from that of the Paleozoic Era.
The Pleistocene Mass Extinction was a Global Event
In the recent history of the earth there have been two periods of accelerated extinction of biota during which the extinction rates were greater than evolutionary causes would predict. These two periods are the end of the Pleistocene Epoch and the modern period.
The Pleistocene extinction, took place over a period of a few thousand years, at the end of the last glacial advance (l8,000 to 8000 BCE). In a relatively short period of time, whether measured in either geologic time, evolutionary time or in terms of human history on earth, a large number of species of mammals and birds disappeared without being replaced. The period of greatest species loss was from 13,000 to 8000 BCE. During this time there was a rapid warming of the planet. Especially impacted species were the larger animals weighing more than 40 kg (88 lbs)The spacing of the extinctions over several thousand years makes it difficult to ascribe to climate events alone. Furthermore, most of the extinct animals were large enough to be conspicuous and edible.
The rate of extinction varied from place to place and through time. The rate of extinction was lowest in Sub-Saharan Africa where modern humans coexisted with the large animals the longest. The rate of extinction increased as distance from the African region increased. The highest rate of extinction occurred in South America.
To some extent the rate of extinction paralleled the spread of modern humans. It was long believed that large mammals were too powerful for humans to hunt. Perhaps this was true for the individual hunter with spear or bow and arrow, but when hunters went out in groups, it is quite possible they could have been very successful hunters of large animals, even using only simple tools.
In Africa, pygmies hunted elephants with primitive tools. The Plains Indians of North America demonstrated they could successfully hunt large animals with primitive weapons. Herds of animals were driven off cliffs or into water by the use of fire and were either subsequently destroyed in the fall or drowned, or at least made far more vulnerable to attack. Modern humans became more sophisticated hunters as they spread from their place of origin in Africa. Places that were isolated from human migration for a longer period of time, such as some islands, suffered less species loss.
The Mass Extinction in North America
The largest North American mammals were hardest hit. Seventy percent of existing species became extinct. Horses and camels, which had evolved in the New World, became extinct on this continent, as did mammoths and mastodons, which had migrated into the New World over the once dry land of the Bering Strait. The ground sloth, saber toothed tiger, dire wolf, giant buffalo, antelope, and the giant beaver also disappeared, and yet there was no concomitant loss of small mammals, plants or aquatic organisms.
The spread of the human species and the state of the cultural development at the end of the Pleistocene suggests that humans were a major factor in this accelerated extinction. A surprising number of the fossilized bones of extinct animals and birds were discovered associated with charcoal and stone tools, such as arrowheads or spear points. Some of the sharpened tools were still embedded in the bones. Humans appeared in North America rather suddenly from Asia, occupied the continent, and began hunting animals that had never had a chance to adapt to this special type of predator.
The most recent extinction is that taking place today. How severe it will be is yet to be determined.
Follow us on Facebook at: https://www.facebook.com/planetearthweekly/