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Biology 4218A

52.4  Wallace: correctly deduced that dramatic differences in flora+fauna were related to depth of channel separating two areas channel so deep it remained barrier to movement o established foundations of biogeography: scientific study of patterns of distribution of populations, species, ecological communities on earth and geological history of area influences kinds of organisms found there o Wallace’s Line: line he drew through Malay Archipelago  flora, fauna, and microorganisms (the biota) of world allow us to divide earth into biogeographic regions: based on taxonomic composition of organisms living in them o boundaries are set where species change dramatically over short distances o biotas differ b/c barriers (oceans, mountains) restrict dispersal of animals btwn o interchanges not been frequent/massive enough to eliminate striking differences that have resulted from speciation+extinction within each region: most species confined  a species found only within certain regions is endemic to region (ex vascular plants of Madagascar b/c of water barriers)  biotas of major biogeographic regions are very different from eachother  3 scientific advancements changed biogeography o acceptance of continental drift theory  Linnaeus believed all organisms created in one place (Paradise) from which they dispersed, and organisms distributed b/c of massive dispersal  Wegner: continental draft; continents changed position over time  280,000,000 yrs ago, continents united to form single land mass (Pangaea), then began to separate, and species evolved o development of phylogenetic taxonomy  biogeographers transform phylogenetic trees into area phylogenies by replacing names of taxa on a tree with names of places where those taxa live(d) o development of island biogeography theory to explain why ocean islands have fewer species that mainland area of same size  2 processes: immigration of new species, extinction of species already present  species pool: list of species on mainland that might possibly colonize  first colonists = new species; as # of species on island increases, they will be members of species already present; rate of arrival of new species decreases until reaches 0  first: few species on island, pop’n may grow large; resources divided among more species; avg pop size of each species will become smaller as number of species increases; smaller pop = more likely to become extinct, and number of species that can possibly become extinct increases as species accumulate;  new arrivals may include pathogens or predators, increases extinction probability therefore rate of extinction increases as # species increases  rate of arrival of new species decreases and extinction race increases, eventually number of species on island should reach an equilibrium at which at they are both equal  if more species than equilibrium, extinction should exceed arrivals, species richness shou
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