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 dynamics Fig c. population changes of local populations in 3 areas Fig 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 extinct m = probability a patch will be colonized Equilibrium metapopulation size P = 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, more distant 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 , 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