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Unformatted text preview: 1 Chapter 24: The Origin of Species Species and Speciation It is not enough to explain how adaptations evolve in a population Evolutionary theory must also explain how new species originate and develop through the subdivision and subsequent divergence of gene pools. p. 472, Campbell & Reece (2005) Speciation is the formation of a new species from an older, immediately ancestral species Species Concepts Biological Species Concept Reproductive Isolation Not necessarily easy to apply Morphological Species Concept Phenotypic differences Paleontological Species Concept Fossil species Ecological Species Concept Filling of ecological niches Competition for resources Phylogenetic Species Concept Evolutionary lineages/genetic history Cohesion Species Concept Persistence of discrete phenotypes (bacteria) Pluralistic Species Concept Combinations of above as appropriate Conspecifics are members of the same species Morphological similarity is not always a good indicator of same species Reproductive Isolation Absolute reproductive isolation means that genes (alleles) do not pass from one population to a second population, one with which the first population is reproductively isolated Note that reproductive isolation does not mean that individuals within two populations are not mating nor producing offspring within populations; instead, if there are offspring, those offspring are not contributing their alleles to either of the parental populations (e.g., because these hybrid offspring are sterile and/or do not survive to reproduce) Also note that reproductive isolation need not be 100%; it is possible for two populations to maintain a large degree of reproductive isolation with some small amount of gene exchange still occurring (a.k.a., introgression) Biological Species Concept The biological species concept is a way of defining species that employs as its number one criteria the concept of reproductive isolation A biological species is a " population or group of populations whose members have the potential to interbreed with one another in nature to produce viable, fertile offspring, but who cannot successfully interbreed with members of other species that is genetically isolated from other such populations." Each species is circumscribed by reproductive barriers that preserve its integrity as a species by blocking genetic mixing with other species. "In the laboratory or in zoos, hybrids can often be produced between two species that do not interbreed in nature. This fact does not nullify the biological species concept. Patterns of Speciation Cladogenesis is branching evolution Only via branching evolution can species increase in number 2 Anagenesis Anagenesis is the transformation of a single ancestral species into a single descendant species ; anagenesis is a mode of speciation Anagenesis involves the extinction of the older, ancestral species Cladogenesis(Adaptive Radiation)...
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- Spring '08