METAPOPULATIONS II.

So far, we have discussed animal examples almost exclusively.

Metapopulations were first appliedto animals

Do they apply to plants?

Plants and metapopulations

Difficult to tell if plants are part of a metapopulation-

Seed bank recruitment vs. immigration

Most patchy distributions seem to beonly partly dependent on meta-population dynamics

Plants and metapopulations

Seem to occur most commonly whenplant inhabits an ephemeral andunpredictable patch

Examples:badger moundsgaps in forest canopy

Example of plant metapopulation

Water hyacinths (Eichhornia paniculata)in Brazil

No seed bank

Subpopulations comeand go

Another example

Primula vulgarisLives under gapsin forest canopy

Relies on seeddispersal to reachnewly formed gaps

Gap grows closed,subpopulation dies

Furbish’s Lousewort (Pedicularia furbishiae)

Endemic to the St. John riverin Maine

Inhabits early-mid successionalstreambanks

Requires ice and flooding to removecompeting species

Metapopulation model appears to apply

Example of source-sink in plants

American SearocketCakile edentula

(Keddy, PA. 1982. Oecologia 52:348-355)

Plant metapopulations and invasions

Metapopulation dynamics do explain therapid spread of invasive species

Small, outlying populations critical to continuing the spread

These are called “nascent foci”

Examples: spread of oak in Britain afterice age; many invasive exotic spp.

Genetics and metapopulations

What are the consequences of thesemovements among subpopulationsfor the subpopulations’ geneticstructure?

Factors influencing genetic diversity in metapopulations

1.Carrying capacity of patches

2. Rate of turnover events (extinctionfollowed by recolonization)

3. Number of sources of colonists inthe 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 ofpatch size and colonization and extinction rates.

A few large patches will have greater genetic diversity than more smallerones with the same overall N.

Metapopulations and genetic diversity

The greatest overall genetic diversitywill theoretically be maintainedwhen:

Some subpopulations have frequentmigration, but others are nearlyisolated

Metapopulations and genetic diversity

LOSS OF GENETIC DIVERSITY:

•If migration among patches does notovercome genetic drift

•If colonization rare and from only oneor very few individuals (foundereffect)

Metapopulation structure does notguarantee genetic diversity!

A botanical exampleCampion (Silene alba) roadside weed

in Virginia

High turnover rate

Poor dispersal

Most subpopulationsfounded by few individuals

Over time, marked loss of genetic diversity

(McCauley et al. 2001)

Landscape ecology vs. metapopulations

How are they different?

Primarily in how they deal with thespace between patches

How are they similar?

Both deal with interactions amonghabitat patches

Landscape ecology

•Patches vary in quality both acrossspace and through time

•There are boundaries between patches

•Movements of organisms and materialsamong landscape elements determineconnectivity

•Patch characteristics and dynamics are afunction of location relative to featuresin the landscape as a whole.

Landscape ecology

(Ricklefs and Miller 2000, p.344)

Metapopulation theory and conservation

Metapopulation theory highlighted needto maintain connectedness amongpopulations

Shifted conservation focus away fromtreating each small population separately

Emphasis on connectivity and movement

Biological corridors

Movement of organisms across alandscape is not necessarily random

Conservation attempts to maintain“travel routes” for organisms todisperse 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 earlysuccessional vegetation in pineplantations of South Carolina

(Haddad et al. 2003. Ecology 84:609-615)

Haddad et al.’s Corridor Test

Two butterfly speciesTwo rodent species

The seeds of four plant speciesPollen 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 usecorridors for movement

•First demonstration that interpatch movement by plants affected byconnectivity

•Overall, 68% more individuals moved toconnected patches rather thanunconnected ones

Haddad et al.’s Corridor Test

Emigration didn’t appear to be affectedby the landscape

If you were going to leave, you did soregardless of the surroundings.

No relationship between taxa and sizeof corridor effect

Summary

•The metapopulation model applies to plants

•Most applicable to ephemeral and unpre-dictable habitats

•Also applies to invasive species- “nascentfoci”

•Genetic diversity is not necessarily maxi-mized in metapopulation

•Landscape ecology adds realism tometapopulation models

Summary continued

•Metapopulation theory emphasized population connectivity and movementsof individuals between them

•Widely applied to reserve design inconservation