Week5 - Distributions of Organisms Three fundamental...

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Distributions of Organisms Three fundamental processes in biogeography: 1. evolution 2. extinction 3. dispersal The relative importance of these processes varies from one group to another. Dispersal: migration by the taxon across a barrier from A to B Vicariance: erection of a barrier between A and B, both of which were already occupied by the taxon The type of phylogenetic pattern observed for dispersal vs vicariance differs. Dispersal The role of successful dispersal in biogeography is an analog of beneficial mutations of the genome - rare, but significant events that are hard to track from step to step. 1. long-distance dispersal my be infrequent and stochastic 2. can’t ignore it just because it’s hard to study For a species to expand it’s range it must be able to: 1. travel to a new area 2. survive the passage 3. establish a viable population at the endpoint 5 - 1
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Long-distance dispersal (aka jump dispersal) three important consequences: 1. mechanism can explain distribution of organisms 2. accounts for similarities of distant biotas 3. emphasizes the impact of humans as transporters of organisms Diffusion Typically has three stages: 1. invasion and range expansion; very slow and may need several introductions 2. after establishment, range expansion is exponential 3. range expansion slows and stabilizes when ecological barriers encountered Secular migration occurs very slowly: hundreds of generations -- long enough for evolution Mechanisms: Active vs Passive Dispersal Active Movement under own power = active: e.g., animals. Passive most organisms disperse by passive means rather than active means Plants, animals, fungi and microbes can disperse passively 5 - 2
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Barriers to dispersal Physiological barriers Ecological and Behavioral barriers Dispersal Routes and Biotic Exchange Corridor: dispersal route that permits the movement of many or most taxa from one region to another Filter: dispersal route that is more restrictive than a corridor.
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Week5 - Distributions of Organisms Three fundamental...

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