Dispersal

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"Three fundamental processes of Biogeography"

  • Speciation
  • Extinction
  • Dispersal: movement beyond distribution limits
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The pattern of Disjunctions: distantly separated populations [Larrea]
  • Dispersalist: C. Darwin, A.R. Wallace, A. Gray
  • Extensionist: C. Lyell, E. Forbes, J. Hooker (Vicariance)
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Ecological (Adaptive) Dispersal
     "why it happens"
  • Movement to new, unused resources (away from parents)
    • Within same habitat
    • Across barrier to new habitat (within range)
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Dispersal as a biogeographic Event
  • Rare and infrequent, seldom observed
  • Fundamental process of biogeography
  • Common in the fossil record (minimum age)
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Successful Dispersal depends on
  • "long distance" transport
  • withstanding unfavorable conditions during travel and upon early arrival
  • establishing a viable population
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Three Kinds of Dispersal Leading to Range Expansion

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Dispersal and Range Expansion
  • Jump Dispersal: long distances over inhospitable habitat
    • example: oceanic islands
    • mostly by volant organisms (flight) ex.: Galapagos Islands
    • rare, large (distance), and "surprising" events
    • explains large discontinuous distributions of some organisms
    • explains taxonomic similarity of distant biotas and populations
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Dispersal and Range Expansion next
















Dispersal and Range Expansion
  • Secular Migration: geological times scale
    • Plants: diversification and spread of flowering plants
    • Animals: spread of camels from North America to S. America and Asia
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Dispersal Mechanisms next
















Passive Dispersal Mechanisms
















Dispersal "strategies" for plants
  • Resistant seeds, spores (floating on salt water)
  • Tiny size for distant transport by wind
  • hitchhikers (phoresy): hooks, hairs for transport by animals
    • animal hitchhikers: flower mites in hummingbird noses
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Barriers to Dispersal
  • Physical
    • human introductions indicate how effective barriers can be (bass in Caribbean)
    • overcome resistant propagules
    • "weeds" are good dispersers (hardy)
  • Physiological
    • land-water
    • salinity for aquatic organisms
    • temperature both low and high (sky islands)
  • Ecological-Behavioral
    • predators
    • strong fliers that won't cross water
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Dispersal Routes
  • Corridors: favorable habitat connecting larger ones
    • Tethyan Sea
    • Bering Land Bridge [map]
    • Panama Isthmus
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Dispersal Routes
  • Filters:blocks or slows passage of some organisms
    • Arabian desert allows movement of animals between Africa and Asia
    • Sunda archipelago reptiles
    • Southwestern forest vertebrates [SW]
    • Panama: freshwater separates Caribbean from Pacific
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Dispersal Routes
  • Sweepstakes Routes: severe barrier that permits rare dispersals
    • Asian snails in the South Pacific
    • South American animals in the Galapagos
  • Plate Tectonics
    • Indian fauna introduced to Asia
    • Terranes
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Factors favoring establishment
  • Appropriate Habitat - Niche
  • Propagule (minimum unit)
    • asexually reproducing plants
    • parthenogenetic geckos
    • gravid females
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  • pagile: distributed passively.
  • parthenogenetic: females developing eggs capable of producing adults, without male fertilization.
  • phoresy: the transport of organisms by other organisms
  • propagule: any part of an organism (colony of organisms) or life stage of its life cycle that can reproduce the species and establish a new population (distribule)
  • vagile: capable of active dispersal
  • volant: capable of sustained flight
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