Species_concepts___speciation_class

Species_concepts___speciation_class - Species concepts...

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Species concepts & Speciation Reading: Chapter 16
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Objectives What is a species? Species concepts Mechanisms of speciation Allopatric, parapatric & sympatric speciation Hybridization & polyploidy
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What is a species???? Species = Latin for “kind”, -taxonomic units to which taxonomists like Linnaeus assigned species Defining “species” has, and continues to be controversial due problems with the establishment of practical criteria for recognizing evolutionary independence As a result, there are many species concepts
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Typological or Morphological Species Concept Type specimen = a single individual (usually) that represents the entire species Specimens are considered to belong to the same species if they agree morphologically with the “Type” of the species However, many species show a continuum of morphological variation Today the “Type Method” is still used, but there is an attempt to select defining characters that have a genetic basis There are clearly written rules for naming and renaming taxa: Botanical Code, Zoological Code etc.
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Typological or Morphological Species Concept: Problems Cryptic Species : species that cannot be distinguished on the basis of their morphological characteristics Phenotypic Plasticity : morphological variation that does not have a genetic basis. Environmentally induced morphological differences
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Biological Species Concept Species are groups of interbreeding natural populations that are reproductively isolated from other such groups (Ernst Mayr, 1942) Individuals within a species resemble each other due to gene flow , resulting from interbreeding Evolutionary criterion is reproductive isolation and interbreeding Legal definition used in U.S. endangered species act
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Biological Species Concept: Problems Asexual Taxa : obviously doesn’t apply Fossil Taxa : cannot be tested Hybridization : difficult to apply the biological species concept to taxa that hybridize
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Some organisms currently considered to be different species hybridize and form viable offspring Coyote Canis latrans Wolf Canis lupus http://www.cws-scf.ec.gc.ca/ Mallard ( Anas platyrhynchos) Northern Pintail ( Anas acuta)
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Hybridization: The Splake Lake Trout Salvelinus namaycush Speckled Trout Salvelinus fontinalis
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Hybridization: Brown (Grizzly) and Polar Bears (Interspecific Hybridization) Inter = between, Intra= among Ursus maritimus Ursus arctos
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A Grolar/ Pizzly/ Grizzlar Bear
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Species_concepts___speciation_class - Species concepts...

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