Chapter 24 The Origin of Specifes

Chapter 24 The Origin of Specifes - Chapter 24 The Origin...

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Chapter 24: The Origin of Species 24.1: The biological species concept emphasizes reproduction isolation - Speciation: the process by which one species splits into two or more species The Biological Species Concept - Described by Ernst Mayr in 1942: a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but not with other groups - Members of a species often resemble each other because their populations are connected by gene flow Reproductive Isolation - The existence of biological factors that impede members or two species from producing viable, fertile offspring o These barriers block gene flow between species and limit the formation of hybrids - Prezygotic barriers: block fertilization from even occurring o Work by stopping members of a different species from even attempting to mate, preventing an attempted mating from being successfully completed, or by hindering fertilization if mating is completed successfully Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Gametic isolation - Postzygotic barriers: contribute to reproductive isolation after the hybrid zygote is formed o Developmental errors can reduce survival among hybrid embryos o Problems after birth can decrease their chances of survival long enough for them to reproduce Reduced hybrid variability Reduced hybrid fertility Hybrid breakdown Limitations of the Biological Species Concept - Although it directs our attention to how speciation occurs (by evolution of reproductive isolation), the number of species to which this concept can be usefully applied is limited - There are many pairs of species that re morphologically and ecologically distinct and yet gene flow occurs between them; in this concept, species are designated by the absence of gene flow Other Definitions of Species
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This note was uploaded on 04/21/2009 for the course BISC 120Lg taught by Professor 11:00-01:50pm during the Fall '06 term at USC.

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Chapter 24 The Origin of Specifes - Chapter 24 The Origin...

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