Dispersal

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Dispersal
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Diffusion

• Gradual movement
• Over several generations

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California Sea Otter

• Thought to be extinct in 1911
• Found at Point Sur in 1914
• More rapid southern expansion

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Jump Dispersal

• 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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Collared Dove Expansion
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Dispersal Polymorphism

• Gymnarrhena micrantha

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Philopatry

• Tendency to disperse near close kin

Beldings Ground Squirrel
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Barriers

• Physical
• human introductions indicate how effective
  barriers can be
• overcome resistant propagules
• "weeds" are good dispersers (hardy)
• Physiological
• land-water
• salinity for aquatic organisms
• temperature both low and high
• Ecological-Behavioral
• predators
• strong fliers that won't cross water

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U.S. Starling Dispersal

• 100 birds added to Central Park in late 1800s

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Gypsy moth

• Accidental introduction at end of 19th century

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River barriers
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Acorn dispersal by Jays

• The more seeds carried, the farther the distance

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Neritina dispersal
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Dispersal Distance
Eucalyptus
Isolated tree
Edge of forest
Longocarpus
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Measuring Dispersal Distance

• Breadth of normal distribution characterized by
  standard deviation (s)
• Variance
• If mean (release point) is 0, distance from
  release site(xi-mean) is di, then
• Distance over time is

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Dispersal vs. range
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Birth nest to yearling nesting
House wren nesting at distances (1000 ft
segments) from nest where hatched
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Dispersal for mating

• Distance from birth site to mating site for the
  Great Tit

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Inbreeding vs. Outbreeding

• In many bird populations, about 50 of the birds
  in an area are immigrants.
• Great Tit study - 22 of pairings were from
  resident males females
• Inbred nestling mortality 27.7
• Outbred nestling mortality 16.2

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Opossum expansion

• Climate related?

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Maple/Hemlock expansion
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Dispersal in Space
Dispersal in Time

• Large seeds and fruits
• Long-lived plants
• Low relative growth rates
• Strong competitive ability
• Predator defenses in plants
• Innate, transient dormancy
• High decay rates of soil seed populations
• Flat dispersal curve
• Stable populations of plants

• Small seeds
• Short-lived plants
• High relative growth rates
• Weak competitive ability
• Predator defenses in seeds
• Enforced dormancy dependent upon burial
• Low decay rates of soil seed populations
• Steep dispersal curve
• Unstable populations of plants

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Seed Dormancy

• Innate dormancy - from when seed first produced
• Induced dormancy - internal, but first induced by
  environmental factor
• Enforced dormancy - environmental factors

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