Metapopulations I.

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Metapopulations I.
So far, we have looked at populations with the
assumption of geographic closure no
immigration, no emigration
What if we relax that assumption?
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What is a metapopulation?
Set of local populations occupying an array of
habitat patches and linked by the movements of
individuals
Movement emigration and immigration not
back-and-forth movements of individuals
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(No Transcript)
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Example of metapopulation spotted owls in
southern CA
(Ricklefs and Miller 2000 p. 331)
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Origin
The term was first used by Richard Levins in
1969 and 1970
Levins model looked at patch occupancy coloniza
tion and extinction events
Also known as the classical model or blinking
light model
What was the persistence time of
the metapopulation overall?
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Does the idea work?
Many species seem to have a metapopulation
structure.
Bull Trout
Butterflies
Pool Frogs
Acorn Woodpeckers
Pikas
Furbishs Lousewort
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Different kinds of patchy populations.

• Classic metapopulation (Levins)

• Mainland-island metapopulation
• migrant flow from big patch to small

• Patchy population (too much migration
• for a metapopulation)

• Separate populations (no migration at all,
• or very little)

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An illustration
(from Harrison and Taylor 1997)
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A closer look at the classical model
dP/dt mP(1-P) eP
P number of occupied patches
e extinction rate
m colonization rate
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The assumptions of the classicalmetapopulation
model

• Growth, regulation, and other dynamics
• of local populations ignored

• Colonization and extinction events are
• instantaneous (no growth/decline phase)

• All patches equally likely to receive new
• immigrants (midfield assumption)

• Patches are all the same size and quality

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The classical model
Immigrants only matter when they colonize an
empty patch
Is a patch occupied, or not?
How long will the metapopulation persist?
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What if we add some realism?
Most of the time, the distance between patches
does matter
Size also matters- patch size and distance from
another patch also interact
Isolated patches that are also large
are relatively more likely to be occupied than
small isolated patches
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Example of size/density interaction
Glanville fritillary butterfly
(Ricklefs and Miller 2000 p. 333)
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Example of size/isolation interaction
Common shrew (sorex araneus)
(Ricklefs and Miller 2000, p. 335)
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The Rescue Effect
Populations may be saved from extinction by
arrival of immigrants
Example acorn woodpecker population in New
Mexico
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Acorn Woodpeckers
Population persistence depends on immigrants from
populations whose dynamics vary independently
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Source-sink dynamics
Some patches are inherently better quality than
others
These patches support growing populations that
produce emigrants
Other patches are poorer quality, and
populations can only be maintained by immigration
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Example Eastern Kingbird
Metapopulation in Charlotte Valley, NY
Inhabited upland, floodplain, and riparian zone
habitats
Demographic rates and movements among breeding
populations were studied for 10 years
M. Murphy. 2000. Cons. Biol. 15737-748.
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Example Eastern Kingbirds
Survival was highest in floodplain,
but productivity was lowest there
Riparian subpopulation was stable, but other two
were declining
(M. Murphy. 2001. Ecology 821304-1318)
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Example Eastern Kingbirds
Modeling suggested that metapopulation overall is
a sink.
(M. Murphy, 2001. Cons Biol. 15737-748)
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Example Eastern Kingbirds
Murphy suggested that creek habitat acted as a
pseudosink
A pseudosink is a patch with density- dependent
effects on demographic rates so it seems
unsustainable if density declined, demographic
rates would improve
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Another Example
Demographic rates in a patch may vary not only
with density, but with environmental conditions-
A patch may be a source one year, and a sink the
next.
Burrowing owls at NAS Lemoore, CA
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Burrowing owls (again)
(Gervais 2002)