Island Biogeography and Meta-population theory

Class 5Class 5

Presentation 2Presentation 2

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

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 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