|
''The Turnover-pulse hypothesis'' was constructed by paleoanthropologist Elisabeth Vrba used to gauge the rate of survival and adaptations within species. The Turnover-pulse hypothesis makes clear predictions regarding the responses and actions of species to changing ecological factors. She defined Turn-over Pulse’s as involving episodes of climatic change that caused geographic isolation in various taxa; the isolation subsequently spurred extinction and speciation in several different clades. The Turnover Pulse Hypothesis is significant because it extends the geographic radiation concept from a single to a multi-clade context. The theory's key factors are based on the sequence of species in the palaeontology of related genera, and environmental aspects in adaptation, survival and extinction. The majority of turnover pulses that occur result in small peaks effecting a small amount of organisms and typically involves a small geographic area. It is important to note that based on Vrba and the Turnover-pulse hypothesis, evolutionary change is caused by physical changes in the environment such as climate change, tectonic plates shifting, and astronomical catastrophes to name a few. ==Theory== Ecosystems periodically experience significant disruptions, these in turn result in mass extinctions and speciation. Climate changes have an effect on all groups, from bacteria to hominids.〔 Modern studies of individual populations have shown large cyclical shifts in phenotype/genotype that correlate with climatic variations. These studies in turn, enable scientists to create a better turnover model. Extinctions often hurt specialists more than generalists, where the generalists will in turn thrive within the environment by utilizing new environmental opportunities, or by moving elsewhere in diaspora to take advantage of other environments. The specialists will experience more extinctions, and a "pulse" of positive and random speciation within their groups. These two events lead to more specialists in isolated areas whereas the generalists will become more spread out. This geographic isolation is a common thread in evolution. It is a key factor in the evolution of species on a grander scale. Thus, the activities causing geographic isolation are unmistakable in the significance of evolutionary mechanisms. This hypothesis was developed to explain the different patterns of evolution seen in African antelopes. Later, it was used in an attempt to explain the speciation and distribution that lead to early hominins and subsequently ''Homo sapiens''. Paleoecologists largely agree that global climatic changes in conjunction with tectonic activity are viable explanatory factors in the extinction of ''A. afarensis'', the origin of ''Homo'', and the changes in behavior ecology leading to archaeological sites. This hypothesis has coincided with several theories including the savannah hypothesis which was later renamed the aridity hypothesis. This environmental theory is used to extend the scope of reason behind the appearance of bipedalism. The hominids went from trees to living on the savannah ground. The increased aridity led to the growth and expansion of the savannah, thus requiring the hominids to traverse on two legs. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Turnover-pulse hypothesis」の詳細全文を読む スポンサード リンク
|