Ch. 12 Metapopulations

• Several local populations interacting

• Models: assume no immigration and emigration

• Many species show metapopulation structure

• Subpopulations differ in growth dynamics

• Local extinctions, re-establishments possible

Metapopulation examples

-Aquatic organisms in lakes

-Caribou occur in 32 herds based on calving grounds, herds mix on wintering grounds

4 conditions define a metapopulation (Hanski)

• 1.suitable habitat only found in discrete patches

• 2.all subpopulations have a risk of extinction

• 3.patches close enough to be recolonized

• 4. local populations growth dynamics not synchronized

• Others: presence of core populations and satellite poplns sufficient criteria

Edith checkerspot butterfly metapopulations and dynamicsFig c. population changes of local populations in 3 areasFig d. population changes of Jasper Ridge data pooled

Two scales operate in metapopulations

• 1. local, within patch

– individuals move– reproduce– population changes and regulation

• 2. metapopulation, between patch

– interactions between patches determine dynamics– dispersal from and colonization of patches

• If no dispersal, patches independent• If lots of dispersal, patch boundaries disappear• If intermediate, local extinctions & colonizations may balance

Extinction & recolonization rates drive metapopulation dynamics

e = probability a patch will go extinctm = probability a patch will be colonized

Equilibrium metapopulation sizeP = 1-e/m

Skipper butterflies:

Occupied habitat patches most likely to be larger patches, closer to other patches

Unoccupied habitat patches most likely to be smaller, moredistant from other patches

Habitat heterogeneity (variety) increases local patch persistence

patch size local populations population persistence

Larger patches patch heterogeneity

If environment is variable, If species is sensitive to changing environment, If a patch has greater variety of habitats for it to use,

-expect less extinction in that patch

Kindvall studied effect of patch habitat variety on fluctuations in the population sizes for bush crickets.

Bush cricket, population variability smaller when more

habitat heterogeneity

Population variability

coefficient of variation of population sizes over time

Habitat heterogeneity

index of the vegetation types (low grassland, high grassland, sparse grassland)

Habitat heterogeneity decreased population variability and prob. of local extinction

Some habitat patches “re-seed” patches that go extinct

James Brown coined term “rescue effect”

Bay checkerspot butterfly

Needs serpentine soils for plants its caterpillars eat

Morgan Hill patch is a large “source” patch, smaller patches are “sinks”

Only smaller patches near Morgan Hill patch are regularly colonized

Frequent extinctions and recolonizations

“Mainland-island” metapopulation structure

Current presence and size of a patch population may be very misleading….

The patch may be populated by immigrants, may not be able to sustain reproduction, then becomes extinct.

If dynamics of local populations are synchronized, then large-scale declines (or increases) may occur

Bay checkerspot, regional drought in 1975-1977, caused synchronized extinction of local populations (its food plant declined)

Skipper butterfly in England

<1920, most chalklands (brown)1960, reduced in range (green)1982, reduced further (black)

Heavily grazed calcareous soils needed, these disappeared in 1900s

Species characteristics influence rates of colonization and extinction

• r-selected species - good reproduction, good dispersal, aiding colonization – result of natural selection

• Flight is an adaptation for dispersal, flightlessness associated with increased environmental homogeneity and habitat persistence

• Asexually reproducing plants usually have lower rates of extinction, but dispersal may be reduced

Species characteristics influence rates of colonization and extinction -2

• smaller animals support larger densities per unit area than larger animals

• smaller endothermic animals have higher metabolic costs, may be hard to fuel if food supply declines

• Of 3 shrews studied on islands, the smallest species with highest metabolic rate had highest extinction rate

Population - a hierarchical context

• 1. Local population, can reasonably determine birth, death, immigration, emigration rates

• 2. Metapopulation, collection of local populations close enough to exchange members and colonize empty patches

• 3. Subspecies, collections of metapopulations in a geographic area; enough isolation for genetic variation to accumulate

• 4. Species itself, collection of all subspecies, the whole range of species included

Iberian lynx<1,000 survive

9 partly isolated populations (genetically, spatially)

Habitat fragmentation created metapopulations

Crucial for lynx survival is…?

Genetic exchange between populations, what is needed for this…?

Suitable habitat corridors