METAPOPULATIONS II.

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METAPOPULATIONS II.
So far, we have discussed animal examples
almost exclusively.
Metapopulations were first applied to animals
Do they apply to plants?
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Plants and metapopulations
Difficult to tell if plants are part of a
metapopulation-
Seed bank recruitment vs. immigration
Most patchy distributions seem to be only partly
dependent on meta- population dynamics
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Plants and metapopulations
Seem to occur most commonly when plant inhabits
an ephemeral and unpredictable patch
Examples badger mounds gaps in forest canopy
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Example of plant metapopulation
Water hyacinths (Eichhornia paniculata) in Brazil
No seed bank
Subpopulations come and go
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Another example
Primula vulgaris
Lives under gaps in forest canopy
Relies on seed dispersal to reach newly formed
gaps
Gap grows closed, subpopulation dies
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Furbishs Lousewort (Pedicularia furbishiae)
Endemic to the St. John river in Maine
Inhabits early-mid successional streambanks
Requires ice and flooding to remove competing
species
Metapopulation model appears to apply
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Example of source-sink in plants
American Searocket Cakile edentula
(Keddy, PA. 1982. Oecologia 52348-355)
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Plant metapopulations and invasions
Metapopulation dynamics do explain the rapid
spread of invasive species
Small, outlying populations critical to
continuing the spread
These are called nascent foci
Examples spread of oak in Britain after ice
age many invasive exotic spp.
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Genetics and metapopulations
What are the consequences of these movements
among subpopulations for the subpopulations
genetic structure?
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Factors influencing genetic diversity in
metapopulations

1. Carrying capacity of patches

2. Rate of turnover events (extinction followed
by recolonization)
3. Number of sources of colonists in the
metapopulation
4. Total number of patches
5. Rate of gene flow among patches
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Metapopulations and genetic diversity
All of these elements combined
Genetic diversity is a function of patch size and
colonization and extinction rates.
A few large patches will have greater genetic
diversity than more smaller ones with the same
overall N.
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Metapopulations and genetic diversity
The greatest overall genetic diversity will
theoretically be maintained when
Some subpopulations have frequent migration, but
others are nearly isolated
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Metapopulations and genetic diversity
LOSS OF GENETIC DIVERSITY

• If migration among patches does not
• overcome genetic drift

• If colonization rare and from only one
• or very few individuals (founder
• effect)

Metapopulation structure does not guarantee
genetic diversity!
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A botanical example
Campion (Silene alba) roadside weed in
Virginia
High turnover rate
Poor dispersal
Over time, marked loss of genetic diversity
(McCauley et al. 2001)
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Landscape ecology vs. metapopulations
How are they similar?
Both deal with interactions among habitat patches
How are they different?
Primarily in how they deal with the space
between patches
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Landscape ecology

• Patches vary in quality both across
• space and through time

• There are boundaries between patches

• Movements of organisms and materials
• among landscape elements determine
• connectivity

• Patch characteristics and dynamics are a
• function of location relative to features
• in the landscape as a whole.

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Landscape ecology
(Ricklefs and Miller 2000, p.344)
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Metapopulation theory and conservation
Metapopulation theory highlighted need to
maintain connectedness among populations
Shifted conservation focus away from treating
each small population separately
Emphasis on connectivity and movement
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Biological corridors
Movement of organisms across a landscape is not
necessarily random
Conservation attempts to maintain travel
routes for organisms to disperse among
subpopulations
Example Cougars in S. CA
(Beier, P. 1995. JWM 5(228-237)
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Biological Corridors
An experimental approach

• Corridors direct movement for which taxa?

• How much effect to corridors have?

• Do corridors increase emigration?

Created patches and corridors of
early successional vegetation in
pine plantations of South Carolina
(Haddad et al. 2003. Ecology 84609-615)
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Haddad et al.s Corridor Test
Two butterfly species
Two rodent species
The seeds of four plant species
Pollen of one plant species
One species of bee
Also examined data from other studies
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Haddad et al.s Corridor Test

• The plants and animals studied did use
• corridors for movement

• First demonstration that interpatch
• movement by plants affected by
• connectivity

• Overall, 68 more individuals moved to
• connected patches rather than
• unconnected ones

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Haddad et al.s Corridor Test
Emigration didnt appear to be affected by the
landscape
If you were going to leave, you did
so regardless of the surroundings.
No relationship between taxa and size of
corridor effect
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Summary

• The metapopulation model applies to plants

• Most applicable to ephemeral and unpre-
• dictable habitats

• Also applies to invasive species- nascent
• foci

• Genetic diversity is not necessarily maxi-
• mized in metapopulation

• Landscape ecology adds realism to
• metapopulation models

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Summary continued

• Metapopulation theory emphasized
• population connectivity and movements
• of individuals between them

• Widely applied to reserve design in
• conservation