Island Biogeography and Meta-population theory

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

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

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. 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

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. 1970. Some demographic and genetic consequences of heterogeneity for biological control. Bull. Ent. Soc. Am. 15:237-240

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