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BIOL 1001 (162)
Tamara Kelly (110)
Chapter 5

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School
York University
Department
Biology
Course
BIOL 1001
Professor
Tamara Kelly
Semester
Winter

Description
SpeciationThe evolution of two or more distinct species from a single ancestral species Due to gene flow popns may diverge from each other when isolatedand create 2 distinct species both popns begin to evolve independently of each otherSpeciation results from genetic isolation due to lack of gene flowand genetic divergence due to selection drift and mutation1 How are species definedidentifiedSpeciesAn evolutionary independent population group of populationsMonophyletic groupAn ancestral population an all its descendantsSpecies are evolutionary independent because no gene flow occurs between them and other speciesCriteria for identifying species 1 The Biological Species Concept criteria for identifying species is based on reproductive isolation If two populations do not interbreed or fail to produce surviving and fertile offspring then the two popns are considered distinct species Logical criteria because no gene flow occurs between populations that do not reproduce with each other Reproductive isolation can result from numerous eventsprocesses essentially gene flow is stopped1 Prezygotic Isolation before zygote prevents individuals of different species from mating 2 Postzygotic isolation after zygoteevent in which the offspring of matings between members of different species do not survive or reproducedis criteria of reproductive isolation cannot be evaluated in fossils or asexually reproducing species2 The Morphospecies Concept Researchers identify species evolutionary independent lineages by difference in shape size and morphological features Logical because these distinguishing features are most likely to occur in popns that are isolated from gene flowindependent Applicable to asexual species and fossils dis CANNOT identify cryptic species those that differ in traits other than morphology dis morphological features used to distinguish species are subjective different people may agreedisagree on distinguishing characteristics3 The Ecological Species Concept Defines species as a set of organism exploiting a single set of resources same range of environmental tolerances and facing the same predatorsparasites This concept emphasizes the role of natural selection certain traits favoured to better exploit resources and tolerate environmental conditions Most useful for identifying asexual eukaryotes bacteria archaea4 The Phylogenetic Species ConceptBased on reconstructing the evolutionary history of populations
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