The megafauna's extinction was analyzed from a diverse sample of books, journals, and articles; the main goal was the addition of new perspective on the studies conducted earlier on and to establish the cause of this extinction. The study was based on Grayson 1977 doubt of the anthropogenic overkill hypothesis. The major factors that influenced Pleistocene extinction included: human impact (overkill theory), which was based on such aspects as extinction in island, Clovis first aspect, and Clovis hunter’s aspect. The second factor that influenced megafauna’s extinction was the climate change theory, which was based on the climatic factors such as rainfall level and the temperature level, which contributed greatly in eliminating principal habitants. Other aspects that contributed to the extinction included overspecialization, some species were more superior as compared to others, and failure to transfer to a more favorable area due to dynamic environmental conditions. The third aspect that leads to Pleistocene extinction was the outbreak of diseases. Diseases were as a result of changes in the diet, environmental conditions, such as coldness or very high temperature. Bacterial diseases were easily spread from one animal to another, especially for the herbivores and the carnivores, hence contributing to their extinction. The fourth factor that influenced the megafauna's extinction was due to the effect of fire on the grasslands. Drought and fire affected the grassland globally, which endangered animals. The burning of grassland scared away animals and hunters could easily spot them because they could not hide for their safety. The fifth factor that led to extinction was the combination of both human impact and climatic changes. This theory mainly combines the effects attributed to the human being and the climate. However, the theories named above had limitations in addressing the extinction issue.
Through research on the literature from various authors on the extinction of the megafauna’s in the North of America, the researcher realizes that there are many studies analyzing the extinction as documented in various books, journals, articles, and other literature. These researches have put the study into various contexts discussing different theories explaining the extinction. These ideas explain the cause of the extinction either by a factor, independently or stating that the extinction is a complex thing. The goal of this paper is to add a new perspective on the various studies conducted on the Megafauna’s Extinction through a review of many factors that have influenced the extinction over the years.
This goal will be achieved through two main divisions of the paper with the first one discussing the various theories explaining the cause of the extinction. The study will focus on four key factors influencing the extinction of the Megafauna’s in the North of America: climate change, human impact (examining the overkill theory as the main factor), and external factors, such as disease, breakdown in the genetic diversity, various astronomical events, and possible combination of the factors. The other part will focus on the conclusion of the study and the various areas for further research to expand the research on the subject. The paper also includes a list of work cited containing a combination of books, articles, and journals done by various authors. The research begins with putting the research into historical context on which various studies on the topic have been conducted.
Grayson (1977) doubted the anthropogenic overkill hypothesis. The study suggested the theory, as it states that the Pleistocene in the North of America was due to the high rate of disappearance of the mammalian genera needs a universal extinction for them to be slightly greater than the general extinction of other vertebrate classes at the time (Wolverton et al. 29). Through an examination of bird extinction, it was found that almost an equal proportion came to extinction at the end of the Pleistocene similar to megafauna. However, the study is refuted by radiocarbon studies in Australia and other countries where it was found out that human beings lived with some megafaunas for a long time, and thus, refuting the theory of quick overkill. There are limited locations over a large area, and many of these have a limited traditional inventory. There is also no sufficient evidence that paleo in India was due to an increased level of game hunting. Additionally, the existence of a large number of wild species in the nineteenth century, despite a huge population in India is also contrary to the theory, thus, the diverse findings by various authors.
Human impact (Overkill Theory). The first group of human beings to arrive in America met a diverse group of some huge mammals, which are currently vanished, that existed in the continent until the end of Pleistocene in various locations (Haynes 6). Different traditions steadily hunted the animals in parts of North America. On the contrary, the experiences of South America, though there was a confirmation of increased population interacting with the fauna, hunting was not very rampant in the region. The relationship between humans and the extinction of various large mammals came to reality in the 1930s where there was sufficient evidence that people had startled the animals and led to their extinction.
The theory of overkill is to a large extent attributed to Martin who came up with the theory and supported it with sufficient details. Though the theory has changed gradually with time, four key things have remained to be significant of the theory, that is, the theory was conventional over archaeological together with the paleontological study and evidence that human settlement in the prehistoric period on various islands was consequently followed by an immense extinction of various vertebrates. Clovis, a group of humans, used to prey on different mammals which are no longer in existence now. Thirdly, Pleistocene extinction of mammals in the North of America happened in the last 11000 years of radiocarbon. Lastly, the Clovis was known to be the first group of human to have hunted big mammals in many areas.
The principles made Martin conclude that the hunters led to the extinction of the animals. His argument was that direct predation, led to the removal herbivore reliant, and the loss of these herbivores made carnivores go to extinction. The theory was rejected through the understanding of western European archaeology, where the climate and vertebrate paleontology has clearly supported the idea that the changes in the number of mammals were related to the changes in the climatic conditions. Various aspects were used to explain the theory better, these include:
These were to prove that human settlement led to extinction of vertebrates on many scenarios. The context was preferable since there is adequate documentation that confirms that human settlement in the prehistoric period consequently led to the extermination of vertebrates. In New Zealand, some of the large birds disappeared after several years of permanent settlement of human beings. Additionally, over 25 vertebrate species also disappeared. On Mangaia, 13 to 17 species also went to extinction while in West Indies, several species of hutias, rodents disappeared peoples’ arrival. Various human acts are believed to have led to this extinction for instance hunting and setting human fires that ruined large forests as well as introducing more competitors and predators (Haynes 22). Hunting, the introduction of other species, and other vegetation led to the extinction of the other species a matter that is well documented in various researches. Island faunas are known to be susceptible to human acts since they are restricted to a particular region that has very high chances of being affected by various environmental changes (Wolverton et al. 40).
The fact that the history has it that people passed through the North of America to the South. It was and remains to be the earliest evidence that human factors are the major causes of extinction of large mammals.
Lack of many kill sites in North America in late years of Pleistocene triggered Martin's research on the theory. Despite the lack of enough sites Martin has extraordinarily explained the theory though he calls for the need to increase the number of sites.
Moreover, the extinction occurred more than 11000 years ago which increases the number of critics of the theory. It is clear that the process of extinction for the various species in North America happened gradually over the years. There are also other chances that there were other factors that would have caused the extinction such as the climatic conditions and other external factors.
Climate Change Theory. At the time of Pleistocene, it was noted that Winscount Ice Sheet departure caused changes in the climatic conditions globally. Temperatures became less consistent which made the winters become very cold, and the summer very hot than previous periods. Rain levels were also varied where some seasons were wet and others dry. The level of waters in the streams lowered, and the water tables also reduced significantly.
These changes led to the elimination of principal habitants and increased the number of those which were few before the changes. The level of competition among the herbivores also increased due to the environmental changes (Bamforth and Grund 1769). Due to the discriminatory evolution, stronger species survived while the weaker ones became extinct. Due to the high demand of principal habitat, a lot of water and foliage, big mammals, unlike small mammals, could not survive in the adverse climatic changes, and so they died.
There are other reasons that caused the extinction of various large animals under the pressures of the climate change and competition for scarce resources which include: overspecialization, the existence of superior species, failure to transfer to a more favorable area, and fast environmental changes that were dangerous. Due to the small size of the smaller mammals, they demand fewer resources and, therefore, take longer to feel the impact of the climatic changes and only start to face the effect long after the large animals begin to adjust and respond to the ecological stresses. These factors led to the extinction of the species, and the strategies to protect the animals from extinction was only short term and only slowed the extinction rate, but the animals eventually died due to selective pressure (Blois et al. 773).
Other repercussions of the climatic change hypothesis are the length of the pregnancy period which argues that due to the inability of some species to change their breeding behaviors, the changes in climatic conditions led to their elimination. Large animals tend to have a longer gestation period while others have a gestation period that is linked to the factors such as temperature and food supply. Thus animals with a gestation period shorter than the favorable climatic changes supported the favorable productivity of the species. Consequently, animals that have a gestation period exceeding the favorable climate reduce the chances of either the mother or her offspring to survive (Faith 1681). For large animals, the gestation period that is linked to the environmental changes were modified to ensure that mother gives birth during favorable periods and thus increasing the chances of survival.
During Pleistocene periods, the environmental changes became unstable and thus unpredictable which reduced their rate of reproduction. The low birth rates due to the changing environmental unpredictability increased the chances of the animals becoming extinct. Uncertainties of the pregnancy period also reduced the fitness of the mother and thus reduced her productivity and also the survival of the offspring. Long gestation periods and limited favorable seasons led to a decline in the population of the large animal species. There was a long time taken for the species to adapt to the new environmental condition which led to a decline in the number of offspring and lowered the reproduction success rates of the species.
Cold period displayed a high level of ecological diversity and thus a diverse fauna at the time of Wisconsin ice sheet, heterogeneity decreased, and thus the fauna variety reduced the diversity of the fauna which therefore became unfounded.
Disease. At the time of the migration in Berengian Bridge, the Homo sapiens came carrying a diet that was entirely based on meat and introduced new bacteria and parasite sites. The meat-based diets were used in Europe during the Paleolithic period. This helped the Homo sapiens in surviving during the migration period transversing the Asian and Berengian ecologies. The change of the diet and lack of experience of the native prey and the hunting behavior of the Homo sapiens also led to the extinction of the species. Diffusion of different diseases to the herbivore population, which the large animals had not adapted to, also reduced the population of large species. Coexistence of similar species also increased the chances of sharing the disease transmitting organisms. Additionally, the complementary domestic dogs may have faced competition with the endemic carnivores and as such, some of the domesticated animals may have also contributed to the introduction of the diseases. However, the theory also accounts just for a small level of extinction since research shows that dogs arrived in countries like Australia roughly 35000 years after human arrival and roughly 30000 years after extinction the megafaunas. The extinction of the large animals was due to the act of their life history against that of small animals (Bamforth et al. 1773). It is believed that small animals have a very high chance of resilience because of their history. Humans are also believed to be the reason since before their migration animals used to migrate, and extinction of the large animals had not been experienced. Diseases that emanated from the people such as Avian Malaria to species like Hawaii led to the extinction of isolated birds.
For a disease to be confirmed as the true cause of extinction, several criteria had to be met. For instance, the pathogen should have a carrier state in the receiving species. The pathogen must also have a high infection rate, be exceptionally fatal and be able to infect several species, and thus, dangerous to humans. Though human beings may be infected, the disease should not be very dangerous to a level of causing an epidemic. However, diseases were also not the only cause of extinction; for the theory to stand, people must remain immunologically unexperienced amidst the endless diffusion of hereditary and pathogenic material.
Several years back, grassland happened to be all over the continent with an estimated proportion of 42% ground cover in all the continents. It was characterized by having few trees and shrubs with the grass being the dominant plant. Over the years the huge portion of the grassland has been affected by the human acts. Some of the reasons for the disturbance the search for space for agriculture and livestock raring (Gill et al. 1101). Climate, Drought, and fire affected the portion of grass globally. Despite the challenges that have endangered the grasses, it has adapted to the adverse effects and can hide underground and be able to recover after the adverse effect of drought, fire and animal grazing. There have been various reasons for the many cases of fire some being attributed to human acts in the forests and others being the lightning in the plantations. Due to the huge portion of grass lands, most wild animals moved from the forests to the open fields of grasslands. This however endangered the animals since it became easy for the hunters to target the animals and for the prey to attack these animals. As a result, a large number of wild animals were killed through hunting, the fires set on the grasslands, and the predators. This led to massive decline in the number of animals and eventually became extinct. The regular fire also reduced the habitat for the animals, and therefore the level of competition for the resources increased which lead to the extinction of those that could not survive the competition.
From the different arguments by the various authors, the studies indicate that none of the two methods is independent. There is a high probability that the climate together with the Homo sapiens led to the extinction of many native animals in Australia and other parts of the world (Anderson 648). The change in the climate characterized by high temperatures, dryness of the surroundings among others, led to a declining number of various species due to the pressure of competition for the limited resources. The hunting behaviors of various people, ignorant of the threat posed to animal species with small populations, also highly contributed to the extermination of these animals (Barnosky et al. 863)
Therefore, from the various theories, each factor led to the dire consequences of bringing an end to the various species. However, there is no factor that can be assumed to be having the full responsibility for the extinction in isolation of the other. In case the climate had not reduced the size of the population, the few immigrants of Homo sapiens migrating to Australia and New World would not have been able to hunt and kill all the animals.
The methods proposed by authors Whittington and Dyke are used in advancing the proposition that human habit of killing animals led to the late Pleistocene extinction. However, there are other factors that fail to neither address the climatic changes nor acknowledge that climate was changing at the time. From the data given by the hunters, hunting habits tend to vary with the changes in the environment. Some researchers also attribute inadequate data in the archives to the movement of the Homo sapiens in all over the continent. However, attaching lack of enough archeological sites influenced by the drastic extinction and migration is doubtful. The lack of enough sites due to the short time frame is not a guarantee for their non-existence.
There is, therefore, a high possibility of combining the opinions of the various authors to have a multidimensional model of elimination. The proposal from Guilday 1967 is that the change in the climate led to a shrink in many habitats, thus, reducing the size of the habitat for a large number of the big mammals. The congestion of the animals in a small place caused competition for the limited resources leading to the extinction of some of the species due to the pressure and stress within the small place (Rule et al. 1484). Additionally, the congestion also increased the chances for the hunters and other prey groups to attack the animals. This is attributed to the fact that there were a large number of preys in a very small area increasing the chances of successful hunting.
Other authors are of the opinion that many hunters and gatherers target large wild animals due to the high chances of succeeding in their game and the perceived fitness brought about by the success (Speth et al. 116).
This is a confirmation that the higher success rates in hunting attributed to the concentration in a small area of the big wild animals in a climatically shrunk area. A combination of these factors has a very high chance of bringing the species into extinction. The amalgamation of the point of view, with some supporting the proposition and others against it is a strong foundation of combining the two to explain the megafaunal extinction in a multidimensional model (Barnosky et al. 857).
Despite the fact that it was very hard to combine two theories due to their diversity, compromise may work. This is evidenced by the fact that the two theories agree that the change in the climatic conditions happened relatively within the same period with the arrival of the Homo sapiens (Faith 1676). Therefore, it is very hard to set apart the two events. As such, it is also clear that it is not possible to separate the effects of the two events on the extinction of the huge animals.
The two theories, however, have challenges and limitations to be addressed. As such, the multidimensional approach of looking at the differences, collecting date and facts for the two approaches as well as merging them into one is recommended to help in the understanding of the phenomenon of Megafaunal extinction.