Lecture 5 - Speciation Darwins mystery of mysteries...

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1 Speciation Darwin’s “mystery of mysteries” Involves the splitting of evolutionary lineages Need not involve adaptation Outline Anagenesis and cladogenesis Species concepts Reproductive isolating mechanisms – Prezygotic – Postzygotic The geography of speciation – Allopatric – Sympatric – Parapatric • Examples Ring species – Reinforcement Adaptive radiations Two basic patterns of evolutionary change can be distinguished – Anagenesis – Cladogenesis Figure 24.2 (b) Cladogenesis (a) Anagenesis What is a species? Are species real entities or a product of the human desire to pigeonhole or classify? How do we define them? Species Concepts The biological species concept , Ernst Mayr – Defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but are unable to produce viable fertile offspring with members of other populations
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2 Similarity between different species. The eastern meadowlark ( Sturnella magna, left) and the western meadowlark ( Sturnella neglecta, right) have similar body shapes and colorations. Nevertheless, they are distinct biological species because their songs and other behaviors are different enough to prevent interbreeding should they meet in the wild. (a) Diversity within a species. As diverse as we may be in appearance, all humans belong to a single biological species ( Homo sapiens ), defined by our capacity to interbreed. (b) Figure 24.3 A, B Biological species concept Focuses the study of speciation on the study of the evolution of reproductive isolation Reproductive isolation Is the existence of biological factors that impede members of two species from producing viable, fertile hybrids Is a combination of various reproductive barriers that may operate either before or after fertilization Limitations of the Biological Species Concept Some species hybridize frequently where their ranges overlap, but maintain their differences elsewhere. Are these two or one species? Biologists often disagree as to whether such situations represent two species or one species with two ecotypes Example: Mimulus aurantiacus (bush monkeyflower) in San Diego County: One species or two? More limitations of the Biological Species Concept The biological species concept cannot be applied to Asexual organisms Fossils Organisms about which little is known regarding their reproduction Other Definitions of Species The morphological species concept Characterizes a species in terms of its body shape, size, and other structural features The paleontological species concept Focuses on morphologically discrete species known only from the fossil record The ecological species concept Views a species in terms of its ecological niche The phylogenetic species concept Defines a species as a set of organisms with a unique genetic history
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3 Reproductive Isolation
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