Dispersal, Colonization and Invasion

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Dispersal, Colonization and Invasion
Dispersal active v. passive Colonization,
Seasonal migrations, and irruptions Population
Growth Diffusion vs. jump dispersal Barriers,
Corridors, Filters, Stepping Stones,
Sweepstakes Recent invasions by exotic species
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Dispersal movement of an organism from its point
of origin. intra-range (ecological)
dispersal extra-range (biogeographic) dispersal
Propagule the stage in life cycle, part of the
organism, or group of organisms that is required
to establish a new reproducing population.
samaras
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Passive Dispersal Strategies - Keywords
Anemochores Hydrochores Anemohydrochores Zoocho
res Anthropochores
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Dispersability Establishment Tradeoffs
after Grime and Jeffery, 1965
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Dispersal Efficiency
Typical dispersal distance is not very far But
exceptions always occur
from Cramer, 1965 Begon et al., 1996
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Colonization expansion of a species through the
establishment of a self-sustaining population in
a new geographic location. Compared to
Seasonal migration annual geographic movements
of organisms
Irruptions episodic explosions in the population
size and range of insects/animals
Gypsy Moth Larvae
Central Europe June 2005
after Begon et al., 1996
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Colonization and Theoretical Population Growth
Consider population growth of propagule in new
area without resource limits (open niche)
Exponential Pop. Growth
r per capita growth rate (intrinsic rate) N
population size
With resource limitations
Logistic Pop. Growth
K carrying capacity
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Population Growth Real Data
Reconstructed pop. growth from fossil pollen
Lab experiments with beetles
after MacDonald, 1993
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Once the per capita rate of population growth (r)
is calculated, the population doubling time (td)
can be estimated as
Td ln2 / r
ln2 is approx. 70, which is typically used in
equation
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Read Technical Box p. 239
Fossil spruce (Picea) pollen grains ( 5000 years
old) found in lake sediments
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Diffusion Dispersal
Defn the expansion of the range of a species
along a discrete front.
Continental scale Eastern Hemlock postglacial
spread
After MacDonald (1993). data from Davis et al.
(1986)
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Jump Dispersal
Defn dispersal of a species across a geographic
area not occupied by the species.
After Mundinger and Hope, 1982 Shigesada and
Kawasaki, 1997
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Geographic Features and Dispersal/Colonization
Barriers Corridors Harmonization Filters e.g.
Great American Exchange Stepping
stones Sweepstakes Routes
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Dispersal Filter
The Isthmus of Panama and the Great American
Exchange
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Dispersal Stepping Stone
after Woodroffe, 1987
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Recent Invasions by Exotics
After Ebenhard, 1988