Chapter 21 - C hapter 21: Speciation What mechanisms...

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Chapter 21: Speciation What mechanisms produce distinct species? o Microevolutionary processes alter the pattern and extent of genetic and phenotypic variation within populations. When these processes differ between populations, the populations will diverge, and they may eventually become so different that we recognize them as distinct species. Speciation —the process of species formation Morphological species concept - the idea that all individuals of a species share measurable traits that distinguish them from individuals of other species. biological species concept - emphasized the dynamic nature of species. o In principle, if the members of two populations interbreed and produce fertile offspring under natural condition, they belong to the same species. o If two populations do not interbreed in nature, or fail to produce fertile offspring when they do, they belong to different species. o In terms of population genetics and evolutionary theory. o The first half of Mayr’s definition notes the genetic cohesiveness of species: populations of the same species experience gene flow, which mixes their genetic material. o Second part, the genetic distinctness of each species: because populations of different species are reproductively isolated, they cannot exchange genetic information. o Best evolutionary definition of a sexually reproducing species. Phylogenetic species concept - uses both morphological and genetic sequence data to define a phylogenetic species as a cluster of populations—the tiniest twigs on the tree—that emerge from the same small branch. o Comprises populations that share a recent evolutionary history Many species exhibit substantial geographical variation o Subspecies- local variants of a species; “race.” When geographically separated populations of a species exhibit dramatic, easily recognized phenotypic variation. o Speciation patterns Ring species Some plant and animal species have a ring-shaped geographical distribution that surrounds uninhabitable terrain.
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Chapter 21 - C hapter 21: Speciation What mechanisms...

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