Species and Speciation Species and Speciation Speciation is the process that produces new species Species A fundamental biological unit Defined by the ability or inability of two individuals to exchange genetic material by producing fertile offspring Become extinct Give rise to new species Species Plot Biological Species Concept BSC Alfred Russel Wallace 1865 Ernst Mayr Groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups Morphospecies Concept States that members of the same species usually look alike More practical Not perfect Ring Species Limitations of the BSC Difficult to apply in real world Cannot be applied to asexual or extinct organisms Does not account for genetic exchange in ring species Does not account for hybridization in plants Interbreeding between different species seen often in plants The species maintain distinct appearances indicating that natural selection works against the hybrid offspring Improving the BSC Ecological species concept ESC A species can sometimes be characterized by its ecological niche Impossible for two species to coexist in the same location if their niches are too similar Evolutionary species concept EvSC Members of a species all share a common ancestry and a common fate These two concepts broaden and generalize the BSC Reproductive Isolation Pre zygotic before fertilization Behavioral Physical Time temporal Space ecological Post zygotic after fertilization Genetic incompatibility Different numbers of chromosomes zygote does not develop offspring are sterile Speciation the evolutionary process of genetic divergence Allopatric Speciation Geographic model of speciation Physical separation between two populations Subspecies may form Two basic mechanisms Dispersal Vicariance Dispersal Derived Speciation Peripatric Speciation Dispersal Derived Speciation Adaptive Radiation Vicariance Derived Speciation Co Speciation Sympatric Speciation Instantaneous Speciation Plant Polyploidy Speciation and Selection Speciation can occur in the presence or absence of selection Natural selection does not always lead to speciation Reproductive isolation can be the result of genetic drift Two ways that natural selection can be involved Sympatric disruptive natural selection Allopatric and adaptive radiation facilitated by natural selection Reinforcement of reproductive isolation Natural Selection in Speciation
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