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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40

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