1. Island Biogeography and Meta-population theory
Class 5
Presentation 2

2. Suggested readings
MacAuthur, R.H. and E.O. Wilson The theory of Island Biogeography. Monographs in Population Biology.
Levins, R Some demographic and genetic consequences of heterogeneity for biological control. Bull. Ent. Soc. Am. 15:

3. Outline
Two major paradigms in conservation biology and their influence on application on policy and application related to conservation

4. Foundations of Island Biogeography
Started with:
MacAuthur, R.H. and E.O. Wilson 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

5. 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

6. Power function
Exponential
10 ha
100 ha

7. Equilibrium model of island biogeography
Near colonizing source
Small island
Ra t e
Far
Extinction
Immigration
Large A B
Number of Species

8. 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

9. Large reserve better than small

10. Contiguous better than fragmented

11. Small reserves close together better than isolated small reserves

12. Proximity to many reserves better than to only one

13. Connectedness better than isolation

14. Less edge better than more edge

15. 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

16. 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

17. 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 Some demographic and genetic consequences of heterogeneity for biological control. Bull. Ent. Soc. Am. 15:

18. Meta-population theory
Habitat islands suffer periodic predictable extinction
Recolonized by dispersers from neighbouring islands
If migration is greater than extinction population persists

19. 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

20. Major difference: small pop & local extinctions
Meta-population
Vacant habitat re-colonized but extinction high
Unoccupied habitat important
Small habitat important useful for persistence
Island Biogeography
Extinctions replaced by re-colonizations
Persistence very rare in reality

21. New insights from meta-population theory
Spatial structure important for population persistence
Results of application have been positive so far

22. 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

23. Examples of key habitat
Spawning grounds for fish
Winter habitat for deer and moose
Moose aquatic feeding areas
Cavity trees

24. 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 non-equilibrium: constant change

25. 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