Suggested readings
MacAuthur, R.H. and E.O. Wilson. 1967. The MacAuthur, R.H. and E.O. Wilson. 1967. The theory of Island Biogeography. theory of Island Biogeography. Monographs in Population Biology.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 Two major paradigms in conservation biology and their influence on application biology and their influence on application on policy and application related to on policy and application related to conservationconservation
Foundations of Island Biogeography Started with:Started with:
MacAuthur, R.H. and E.O. Wilson. 1967. The MacAuthur, R.H. and E.O. Wilson. 1967. The theory of Island Biogeography. theory of Island Biogeography. Monographs in Population Biology.Monographs in Population Biology.
They proposed that suitable habitat and They proposed that suitable habitat and species diversity vary directlyspecies diversity vary directly
I.e. more habitat more speciesI.e. more habitat more species
Foundations of Island Biogeography Relationship could be expressed:Relationship could be expressed:
S = cAS = cAzz
S = Number of speciesS = Number of speciesc = taxon specific constantc = taxon specific constantA = Area of islandA = Area of islandz z = extinction coefficient= extinction coefficient
Species-Area Curves & Their Relationship
05
1015
2025
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Area (Log Scale)
Spec
ies
Rich
ness Power
function
Exponential
10 ha100 ha
Near colonizing source
Far
Small island
LargeImmigration
Extinction
AB
Number of Species
Ra t e
Equilibrium model of island biogeography
Equilibrium theory of Isld Biogeography Predicts that number of species will be Predicts that number of species will be
greatest on large islands near mainlandgreatest on large islands near mainland As more species inhabited island As more species inhabited island
colonization rate becomes lower colonization rate becomes lower Not all species have equal probability to Not all species have equal probability to
migrate (filtered out)migrate (filtered out) Stepping stone islands can speed rate of Stepping stone islands can speed rate of
migrationmigration
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 Any population that is a population of is a population of local populations local populations which are established which are established by colonists, survive by colonists, survive for a while, send out for a while, send out migrants and migrants and eventually disappear eventually disappear (Levins 1970)(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 Habitat islands suffer periodic predictable extinctionextinction
Recolonized by dispersers from Recolonized by dispersers from neighbouring islandsneighbouring islands
If migration is greater than extinction If migration is greater than extinction population persistspopulation persists
Meta-population theory
Large population: rate of sub-population Large population: rate of sub-population extinction not importantextinction not important
If extinction rate varies with time never get If extinction rate varies with time never get equilibrium populationequilibrium population
Theory suggests: important to define what Theory suggests: important to define what is habitat and what is notis habitat and what is not
Major difference: small pop & local extinctionsIsland BiogeographyIsland Biogeography
Extinctions replaced Extinctions replaced by re-colonizationsby re-colonizations
Persistence very rare Persistence very rare in realityin reality
Meta-population
Vacant habitat re-colonized but extinction high
Unoccupied habitat important
Small habitat important useful for persistence
New insights from meta-population theory Spatial structure important for population Spatial structure important for population
persistencepersistence Results of application have been positive so Results of application have been positive so
farfar
Refinements of meta-population theory All habitat not equal All habitat not equal ““Source” habitat = produce surplus, support Source” habitat = produce surplus, support
long term populationlong term population ““Sink” habitat = population cannot replace Sink” habitat = population cannot replace
itself without immigrationitself without immigration Key habitat important not necessarily Key habitat important not necessarily
habitat that supports high populationhabitat that supports high population
Examples of key habitat
Spawning grounds for fishSpawning grounds for fish Winter habitat for deer and mooseWinter habitat for deer and moose Moose aquatic feeding areasMoose aquatic feeding areas Cavity treesCavity trees
Summary
Meta-population theory has refined island Meta-population theory has refined island biogeography theorybiogeography theory
Meta-population theory suggests habitat Meta-population theory suggests habitat variability important for population variability important for population persistencepersistence
Shifted our view of ecosystems as non-Shifted our view of ecosystems as non-equilibrium: constant changeequilibrium: constant change
Summary
Shifted our attempts from preserving areas Shifted our attempts from preserving areas (e.g. parks) to influencing ecosystem (e.g. parks) to influencing ecosystem processes such as fire, water regimes, processes such as fire, water regimes, hebivory, nutrient flow.hebivory, nutrient flow. E.g. 1) grasslands and grazingE.g. 1) grasslands and grazing
2) forest fire2) forest fire