Evolution- Pace of Speciation
Terms in this set (7)
Distinguish between punctuated equilibria and gradual speciation.
Species arise gradually through evolution of traits that distinguish them from ancestral forms. The gradual speciation concept is based on Darwin's original concept of speciation. In the 1970s, Gould and Eldredge proposed that instead of slow gradual change, species arose suddenly and then remained in stasis, morphologically and genetically stable for most of their evolutionary history. The theory of punctuated equilibria generated considerable controversy. Consensus today is that both modes of speciation are represented among organisms.
Describe factors that affect speciation rates.
Genetic and environmental factors affect speciation rates. Speciation is a genetic event based on reproductive isolation. Reproductive isolation can arise due to chance events in the environmental or from behavioral or morphological variation. Genetic factors can enhance reproductive isolation once initiated, enhancing the likelihood and rate of speciation. There are several methods that can be used to determine speciation rates in organisms.
Give examples of speciation rates and explain methods for determining speciation rates.
There are different types of speciation rates, and different methods are used to determine them. (1) Some plants, such as Gladiolus, speciate slowly, consistent with the gradual speciation model. However, scientists have found punctuated equilibria patterns among marine fossils, and have recreated such patterns among lab-cultured bacteria. (2) The fossil record provides data that can be used to determine speciation rates. Since fossilization events are rare and occur under varying circumstances, such data is prone to error and misinterpretation. (3) The molecular clock model uses genetic and molecular data to determine speciation rates. It assumes a constant rate of neutral mutation. Although this assumption may not be met, when genetic divergence is calibrated to dates of known environmental events, speciation rates can be established with high confidence. Among organisms surveyed, speciation rates vary by four orders or magnitude, from one species per 4,000 years in cichlid fishes to one per 40 million years in beetles.
Smooth, gradual evolutionary change.
Species traits relatively constant, interupted by brief, sudden, and abrupt strong selective pressures.
Evolutionary process by which populations diverge to form new species.
Evolutionary steady-state condition in which little change is occurring.
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