Section 3

Formation of Species

• According to the biological species concept, a species is a population of organisms that can successfully interbreed but cannot breed with other groups.

• Geographic isolation results from the separation of population subgroups by geographic barriers. Geographic isolation may lead to allopatric speciation.

Vocabulary speciation (p. 326) morphology (p. 326) biological species concept

geographic isolation (p. 32?) allopatric speciation (p. 32B) reproductive isolation

• Reproductive isolation results from the separation of population subgroups by barriers to successful breeding. Reproductive isolation may lead to sympatric speciation.

• In the gradual model of speciation, species undergo small changes at a constant rate. In the punctuated equilibrium model, new species arise abruptly, differ greatly from their ancestors, and then change little over long periods.

prezygotic isolation (p. 32B) postzygotic isolation (p. 32B) sympatric speciation (p. 329)

gradualism (p. 330) punctuated equilibrium

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