Dispersal
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Diffusion
• Gradual movement• Over several generations
California Sea Otter• Thought to be extinct in 1911
• Found at Point Sur in 1914
• More rapid southern expansion
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
Collared Dove Expansion
Dispersal Polymorphism
• Gymnarrhena micrantha
Philopatry
• Tendency to disperse near close kin
Belding’s Ground Squirrel
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 1800’s
Gypsy moth
• Accidental introduction at end of 19th century
River barriers
Acorn dispersal by Jays
The more seeds carried, the farther the distance
Neritina dispersal
Dispersal Distance
Edge of forest
Isolated tree
Eucalyptus
Longocarpus
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:
€
s2 =1
N(x i
i=1
N
∑ − x_
)2
€
s2 =1
Ndi2
i=1
N
∑
€
Distance = # dispersal_ days* s2
Dispersal vs. range
Birth nest to yearling nesting
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5
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Distance
House wren nesting at distances (1000 ft segments) from nest where hatched
Dispersal for mating
Distance from birth site to mating site for the Great Tit
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%
Opossum expansion
Climate related?
Maple/Hemlock expansion
• 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
Dispersal in Space Dispersal in Time
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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