Evidence supporting the prehistoric overkill hypothesis includes the persistence of megafauna on some islands for millennia past the disappearance of their continental cousins. For instance, there are ambiguities around the timing of sudden Australian megafauna extinctions. There are some inconsistencies between the current available data and the prehistoric overkill hypothesis. the extinction of the woolly mammoth allowed the extensive grassland to become birch forest, then subsequent forest fires changed the climate.climate change associated with the advance and retreat of major ice caps or ice sheets.There are three main hypotheses to explain this extinction: There is no evidence of megafaunal extinctions at the height of the Last Glacial Maximum, suggesting that increased cold and glaciation were not factors in the Pleistocene extinction. The increased extent of extinction mirrors the migration pattern of modern humans: the further away from Africa, the more recently humans inhabited the area, the less time those environments (including its megafauna) had to become accustomed to humans (and vice versa). These continents had no known native species of Hominoidea (apes) at all, so no species of Hominidae (greater apes) or Homo. This may relate to non-African megafauna and Homo sapiens not having evolved as species alongside each other. It was only in Australia and the Americas that extinction occurred at family taxonomic levels or higher. The proportion of megafauna extinctions is progressively larger the further the human migratory distance from Africa, with the highest extinction rates in Australia, and North and South America.Įxtinctions in the Americas eliminated all mammals larger than 100 kg of South American origin, including those which migrated north in the Great American Interchange. The Late Pleistocene saw the extinction of many mammals weighing more than 40 kg. The proportion of extinct large mammal species (more than or equal to 10 kg) in each country during the last 132 000 years, only counting extinctions earlier than 1000 years BP.jpg South America, Central America, and the CaribbeanĪustralia, New Guinea, New Zealand, and neighbouring islands. ![]() Indian subcontinent, Southeast Asia, and southern China Ī variant of the former possibility is the second-order predation hypothesis (see § related below), which focuses more on the indirect damage caused by overcompetition with nonhuman predators.Įxtinctions by biogeographic realm Summary Extinctions range of the continental large and medium-sized mammals from 40,000–4,000 years BP in different biogeographic realms Biogeographic realm A notable modern human presence first appeared during the Middle Pleistocene in Africa, and started to establish continuous, permanent populations across Eurasia and in Australia-New Guinea from 65-50,000 years BP, and across the Americas south of the Laurentide Ice Sheet from around 16,000 years BP. ![]() Another is that the widespread appearance of humans caused stress on animal populations via overkill or competition. ![]() One possible explanation is that natural climate change related to the Last Glacial Maximum was significantly different from previous instances of climate change. The unusually large scale of megafaunal extinction during this time period has led scientists to search for unique circumstances to explain it. Peak of extinctions in north Eurasia and the Americas occurred during the transition from the Pleistocene to the Holocene epoch (13,000 BCE to 8,000 BCE), except Africa and southern Asia. The main difference from other extinctions is the uncompensated extinction of megafauna, that was a convenient prey for early humans. Major extinctions were incurred in Australia beginning approximately 50,000 years ago and in the Americas about 15,000 years ago, coinciding in time with the early human migrations into these regions. The timing and severity of the extinctions varied by region and are thought to have been driven by varying combinations of human and climatic factors. The extinctions during the Late Pleistocene are differentiated from previous extinctions earlier in the Pleistocene by the widespread absence of ecological succession to replace these extinct species, and the regime shift of previously established faunal relationships and habitats as a consequence. The Late Pleistocene (~129,000-11,700 years Before Present) saw extinctions of numerous predominantly megafaunal species, which resulted in a collapse in faunal density and diversity across the globe. ![]() Late Pleistocene landscape of northern Spain, by Mauricio Antón (left to right: Equus ferus, Mammuthus primigenius, Rangifer tarandus, Panthera spelaea, Coelodonta antiquitatis)
0 Comments
Leave a Reply. |