Mar11_Species - Integrative Biology 200A "PRINCIPLES OF...

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1 Integrative Biology 200A "PRINCIPLES OF PHYLOGENETICS" Spring 2008 University of California, Berkeley B.D. Mishler March 11, 2008: Species Concepts I. Importance of the species problem a. nomenclatorial requirements (all organisms must belong to a species). b. practicality -- need to organize diversity, summarize information, communicate, give names to things. c. legal issues -- endangered species legislation; conservation c. connection to evolutionary theory -- desire to have species as units functioning in process theories (but which process theories? how to connect units and theories without circularity?) d. philosophical concerns -- need to be clear about properties of units: sets vs. individuals, universalism vs. pluralism. II. Quasi-historical outline: a. typological or essentialist approach (i.e., systematics through Linnaeus) b. phenetic, morphological, or "natural" approach - older botanists (Gray, Bentham, Hooker) plus many recent botanists (Cronquist, Levin, Sokal & Crovello) - some recent cladists (!) (Nelson & Platnick, Cracraft, Nixon & Wheeler) c. "biological" species concept: interbreeding groups - classic isolation approach (most zoologists, e.g., Mayr, Dobzhansky) - newer recognition approach (some zoologists, see Paterson) d. "evolutionary" species concept: lineages (Simpson, Wiley) e. "ecological" species concept: niches (Van Valen) f. "species as individual": integrated, cohesive units with spatio-temporal boundaries (Ghiselin, Hull) g. "phylogenetic" species concept: basal monophyletic groups (will return later)
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2 III. Reason for the existence of a species problem: a. most of the above concepts and criteria conflict in most real cases -- different concepts (and processes) "pick out" different groups in each particular case, thus the implied correspondence between different criteria relied on by the BSC (and phenetic concepts) is abundantly falsified. b. operationality -- how to apply various concepts in a practical sense. c. what causes integration/cohesion of species? -- concerns: - breeding relationships are often clinal and/or non-transitive (what does "potential" interbreeding mean?) - gene flow is often very limited or lacking (what causes the evident distinctness of many asexual species?) - what is a niche? - developmental constraints (phylogenetic inertia)? d. what are the spatio-temporal boundaries of species? - monophyly? - origin? - extinction? IV. The winning argument for phylogenetic classification (review) The debate over classification has a long and checkered history (see Hull 1988; Stevens, 1994). A conceptual upheaval in the 1970's and 80's resulted in a true scientic revolution -- Hennigian Phylogenetic Systematics. Many issues were at stake in that era, foremost of which was the nature of taxa. Are they just convenient groupings of organisms with similar features, or are they lineages, marked by homologies? A general, if not completely universal consensus has been reached, that taxa are (or at least should be) the latter (Hennig, 1966; Nelson, 1973; Farris,
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This note was uploaded on 08/01/2008 for the course IB 200 taught by Professor Lindberg,mishler,will during the Spring '08 term at University of California, Berkeley.

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Mar11_Species - Integrative Biology 200A "PRINCIPLES OF...

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