Transcript Metapopulations II

METAPOPULATIONS II.
So far, we have discussed animal
examples almost exclusively.
Metapopulations were first applied
to animals
Do they apply to plants?
Plants and metapopulations
Difficult to tell if plants are part of a
metapopulationSeed bank recruitment vs. immigration
Most patchy distributions seem to be
only partly dependent on metapopulation dynamics
Plants and metapopulations
Seem to occur most commonly when
plant inhabits an ephemeral and
unpredictable patch
Examples:
badger mounds
gaps in forest canopy
Example of plant metapopulation
Water hyacinths (Eichhornia paniculata)
in Brazil
No seed bank
Subpopulations come
and go
Another example
Primula vulgaris
Lives under gaps
in forest canopy
Relies on seed
dispersal to reach
newly formed gaps
Gap grows closed,
subpopulation dies
Furbish’s 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
Example of source-sink in plants
American Searocket
Cakile edentula
(Keddy, PA. 1982. Oecologia 52:348-355)
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.
Genetics and metapopulations
What are the consequences of these
movements among subpopulations
for the subpopulations’ genetic
structure?
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
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.
Metapopulations and genetic diversity
The greatest overall genetic diversity
will theoretically be maintained
when:
Some subpopulations have frequent
migration, but others are nearly
isolated
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!
A botanical example
Campion (Silene alba) roadside weed
in Virginia
High turnover rate
Poor dispersal
Most subpopulations
founded by few individuals
Over time, marked loss of genetic
diversity
(McCauley et al. 2001)
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
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.
Landscape ecology
(Ricklefs and Miller 2000, p.344)
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
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)
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 84:609-615)
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
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
Haddad et al.’s Corridor Test
Emigration didn’t 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
Summary
•The metapopulation model applies to plants
•Most applicable to ephemeral and unpredictable habitats
•Also applies to invasive species- “nascent
foci”
•Genetic diversity is not necessarily maximized in metapopulation
•Landscape ecology adds realism to
metapopulation models
Summary continued
•Metapopulation theory emphasized
population connectivity and movements
of individuals between them
•Widely applied to reserve design in
conservation