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Lecture 7 - Chapter 24, Sections 1 and 2 - Speciation

Lecture 7 - Chapter 24, Sections 1 and 2 - Speciation - Two...

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Speciation 2 Two basic patterns of speciation – Anagenesis (phyletic or vertical evolution) transforms one species into another – Cladogenesis (branching evolution) is the splitting of a gene pool, giving rise to one or more new species Anagenesis Cladogenesis 3 Species = fundamental unit of organization in nature (unit of classification and rank) Ornithologist Ernst Mayr identified 137 birds in Papua New Guinea Native Papuans already had names for 136 species 4 Species Concepts Morphological : defines a species by structural features (different species look different from each other) Paleontological : focuses on morphologically discrete species known only from the fossil record Ecological : (habitat) views a species in terms of its ecological niche Phylogenetic : defines a species as a set of organisms with a unique genetic history Biological : actually or potentially capable of interbreeding (e.g. all dogs, all pigeons, etc)
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5 Biological species concept is most popular, but does not work in all situations • Fossils Asexual taxa Taxa not amenable to breeding studies 6 No species concept works in all situations Many species have few distinguishing morphological characters Often have too little information to apply ecological or phylogenetic concepts Fossils rarely distinguish taxa down to the species level…. 7 Two types of reproductive barriers I) Prezygotic II) Postzygotic 8 Pre zygotic barriers impede mating or hinder fertilization if mating does occur: 1. Habitat isolation ( wrong place ) 2. Temporal isolation ( wrong time ) 3. Behavioral isolation ( no attraction ) 4. Mechanical isolation ( can’t copulate/pollinate ) 5. Gametic isolation ( can’t fertilize )
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