Turnover-pulse hypothesis

The turnover-pulse hypothesis was constructed by paleoanthropologist Elisabeth Vrba, and is used to gauge the rate of survival and adaptation within species. The turnover-pulse hypothesis makes clear predictions regarding the responses of species to changing ecological factors. She defined turnover pulses as involving episodes of climatic change which 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 features 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 affecting a small number of species, and typically involve 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 plate shifting, and astronomical catastrophes, among other things.

Ecosystems periodically experience significant disruptions; these in turn result in mass extinctions and speciation. This would imply that 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, wherein the generalists will thrive within the environment by exploiting new environmental opportunities, or by moving elsewhere in diasporas 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 ubiquitous.

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 events causing geographic isolation are unmistakable in their significance as evolutionary mechanisms.

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