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Island Biogeography and Meta-population theory Class 5 Presentation 2 Suggested readings MacAuthur, R.H. and E.O. Wilson. 1967. The theory of Island Biogeography. Monographs in Population Biology. Levins, R. 1970. Some demographic and genetic consequences of heterogeneity for biological control. Bull. Ent. Soc. Am. 15:237-240 Outline Two major paradigms in conservation biology and their influence on application on policy and application related to conservation Foundations of Island Biogeography Started with: MacAuthur, R.H. and E.O. Wilson. 1967. The theory of Island Biogeography. Monographs in Population Biology. They proposed that suitable habitat and species diversity vary directly I.e. more habitat more species Foundations of Island Biogeography Relationship could be expressed: S = cAz S = Number of species c = taxon specific constant A = Area of island z = extinction coefficient Species Richness Species-Area Curves & Their Relationship 25 20 15 10 5 0 Power function Exponential 1 2 3 4 5 6 7 8 9 10 11 12 13 14 10 ha 100 ha Area (Log Scale) Equilibrium model of island biogeography Near colonizing source Small island R a Far t Immigration e Extinction Large A B Number of Species Equilibrium theory of Isld Biogeography Predicts that number of species will be greatest on large islands near mainland As more species inhabited island colonization rate becomes lower Not all species have equal probability to migrate (filtered out) Stepping stone islands can speed rate of migration Large reserve better than small Contiguous better than fragmented Small reserves close together better than isolated small reserves Proximity to many reserves better than to only one Connectedness better than isolation Less edge better than more edge Problems with island biogeography •Unable to answer important question such as: which species would be found in new areas •Actual extinction rates lower than predicted •Needed new theory to answer question on persistence of small populations Origin: Meta-population theory • First described in the 1950’s •First experimental evidence 1958 •Found that population of predator and prey were more stable (less oscillation) and persistence increased when habitat was more heterogeneous •Found that small populations sometimes occupy small habitats temporarily Definition: Meta-population Any population that is a population of local populations which are established by colonists, survive for a while, send out migrants and eventually disappear (Levins 1970) Levins, R. 1970. Some demographic and genetic consequences of heterogeneity for biological control. Bull. Ent. Soc. Am. 15:237-240 Meta-population theory Habitat islands suffer periodic predictable extinction Recolonized by dispersers from neighbouring islands If migration is greater than extinction population persists Meta-population theory Large population: rate of sub-population extinction not important If extinction rate varies with time never get equilibrium population Theory suggests: important to define what is habitat and what is not Major difference: small pop & local extinctions Island Biogeography Extinctions replaced by re-colonizations Persistence very rare in reality Meta-population Vacant habitat recolonized but extinction high Unoccupied habitat important Small habitat important useful for persistence New insights from metapopulation theory Spatial structure important for population persistence Results of application have been positive so far Refinements of meta-population theory All habitat not equal “Source” habitat = produce surplus, support long term population “Sink” habitat = population cannot replace itself without immigration Key habitat important not necessarily habitat that supports high population Examples of key habitat Spawning grounds for fish Winter habitat for deer and moose Moose aquatic feeding areas Cavity trees Summary Meta-population theory has refined island biogeography theory Meta-population theory suggests habitat variability important for population persistence Shifted our view of ecosystems as nonequilibrium: constant change Summary Shifted our attempts from preserving areas (e.g. parks) to influencing ecosystem processes such as fire, water regimes, hebivory, nutrient flow. E.g. 1) grasslands and grazing 2) forest fire