Dispersal

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Dispersal

• Movement of species leading to range expansion
• Hotly debated
• Dispersalists vs. Extensionists
• Continental drift changed debate
• Long-distance distance dispersal vs. vicariance
• Read Box 6.1

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Diffusion Dispersal

• Slow expansion from previous range into new areas
• Gradual process as species acclimate to
  conditions and taxa at margins of range
• Can follow jump dispersal (next example)

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• Cattle egret (Bubulcus ibis)
• Arrived by flying from Africa in late 1800s

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• European starling (Sturnus vulgaris)
• Intro to Central Park in 1896
• Wanted birds of Shakespeare

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• Oaks across Britain and Ireland

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Jump Dispersal

• Species skips over area outside its range to
  new location
• Island colonization
• Some species lacking from islands limited
  ability to disperse (mammals, amphibians,
  freshwater fishes)
• Also occurs across continents

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Recolonization of Krakatau
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Secular Dispersal

• Evolutionary divergence through range expansion
• Evolutionary time scale

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Mechanisms of Dispersal

• Active
• Capacity to travel long distances (flight,
  walking, or swimming)
• Best example are migratory animals

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Migratory route of golden plover (Pluvialis
dominica)
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Mechanisms of Dispersal

• Passive
• Wind, water, or on animals
• Plants best examples
• Also animals (insects), fungi, and bacteria
• Phoresy animal hitching a ride on another
  animal for dispersal

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Water Dispersal
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Phoresy
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Barriers

• Long-distance dispersal
• Encounter obstacles
• Unfavorable environmental conditions
• Tolerate, overcome, or dead end?

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Physiological Barriers

• Conditions fall outside range of tolerance
• Not able to cross barriers
• History of area may have allowed passage and
  distributions seen today
• Freshwater lake fishes only found in multiple
  locations if lakes were connected at one time
• Some lakes are fishless not because of
  tolerance
• Marine fish vs. freshwater fish

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v
Sheephead minnow (Cyprinodon variegatus)
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Contrast with Centrarchids
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Differences in mountain barriers temperate
vs. tropics
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Mammals, reptiles, etc. aided by past vegatation
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Temporal barriers temperate/polar water
bodies. Movement over ice
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Ecological Barriers

• Competition
• Predation
• Habitats refusal to cross

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Corridors

• Allow dispersal by permitting movement
• Contemporary examples
• Historical account for related of different
  species or even same species in widely separated
  regions

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Tethyan Seaway
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Filters

• Restrictive dispersal pathway
• Conditions restrictive to some species, not
  others
• Can be biotic or abiotic

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Two-way Filter
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