1. R. H. MacArthur E. O. Wilson 1963, 1967 Species richness on islands:
Tended toward equilibrium number, Ŝ
Resulted from balance between rates of immigration and extinction

2. Extinction vs. colonization
Immigration rate
Extinction rate
Number of species P Ŝ
Size of species pool

3. More realistically: Inflections due to interactions among species
Extinction rate
Immigration rate
Immigration rates differ among species
Competition among species increases as more species arrive P
Number of species

4. Still more realistically:
Extinction and immigration probabilities related to island area and distance from source
Immigration to near islands more likely than to far
vs.
Extinction on small islands more likely than on large
vs.
Archipelago
Mainland

5. Area and distance combined:
near
small
Extinction rate
Immigration rate Ŝ
Species richness for a far, small island Ŝ
Species richness for a near, large island
large
far P
Number of species

6. Conceptually powerful tool:
Can be used to make predictions across a broad array of circumstances

7. Near vs. far archipelagos:B A
Near A B C C B A
Far

8. Distance vs. area: C B A
Large A B C
Small C B A

9. Stepping stones: C B A
Without A B C C B A
With

10. Effects of clumping: C B A
Scattered C B A C B A
Clumped

11. Extinction Immigration
Modifications:
Area Distance
Extinction Immigration
Target effect
MacArthur-
Wilson
Rescue effect

12. Predictions
Number of species on an island constant, but turnover is considerable
Relationship between island isolation and immigration
Relationship between island size and richness
Species area curve

13. Species-area curve S = cAZ Where: S = richness c = slope of curve
A = area, and
z is really hard to explain (usually 0.2 to 0.4)
Number of species
Island area

14. S = cAZ  Qualitative comparisons
Archipelago B
Predictions of IB hold for both Archipelagos
S greater overall for Archipelago B
Number of species
Archipelago A
Island area

15. log (S=cAZ)  log S = log c + z log A
Why?
Plot of logS vs. logA is linear
z has meaning!
Slope of the logS/logA line
The rate of increase of species per unit area
(or is it?)
c is intercept of the logS/logA line
Not of a lot of analytical interest (generally)
Allows quantitative analysis:
Island biogeography’s predictions
Comparisons of biotas

16. c differs, z is the same
Predictions of IB hold for both
S greater overall for Archipelago A
Log species
Archipelago A
Archipelago B
Log area

17. Archipelago A
Log species
Archipelago B
c and z differ
Predictions of IB hold for Archipelago A only
Log area

18. Species-area curves Probably broadest application of IB theory
Used to explore relationships between S and:
Space
Time
Body size
Habitat diversity
Sampling effort
Speciation
Extinction
Coevolution
[Rosenzweig, M. L Species diversity in space and time. Cambridge University Press]

19. Caveat
Species-area relationships do not validate island biogeography, per se
Other reasons S could increase with area:
On larger islands, the more you look, the more species you find (sampling issue)
Speciation more likely on larger islands
Large islands influenced proportionally less by disturbances
Fewer catastrophes, more successional diversity
Large islands contain more habitats

20. Pros of IB Elegant Rigorous Currency is tractable Simple
A few causes explain multiple effects
Rigorous
Yields testable, numerical predictions
Facilitates quantitative analysis
Falsifiable
Currency is tractable
Species richness
Important to research and conservation

21. Cons of IB Biological meaning?
Non-mechanistic
No biology involved beyond immigration and extinction rates
Very few estimates of extinction and immigration rates, or species turnover exist
How well does simple species richness portray community structure and stability?
Application to landscape ecology & conservation?
Are patches on a landscape analogous to oceanic islands?

22. What is biodiversity? Number of species?
Relative abundance of species?
Trophic interactions?
Energy/nutrient flows?

23. How do we measure it? Count things: Estimate interactions:
Vertebrates only?
Invertebrates, too?
Estimate interactions:
Food webs?
Rates of energy transfer?
At what scale?
richness
area/time

24. I dunno… No 1 universal approach…
Match the approach to the scale of observation
Temporal, spatial, ecological
Sounds like….
… hierarchy theory?

25. On landscape scales, maybe…?
Competition
Predation/herbivory
Disturbance
Coevolution
Succession
Parasitism
Commensalism
Mutualism
Complex interactions (indirect effects)
Transfer/flow of energy and nutrients
Island Biogeography
L - n L?
L + n

26. Discussion What is biodiversity, really?
How do we understand and measure it on large scales
When is island biogeography appropriate to landscape ecology, when not?
How much of island biogeography is implicit in our understanding of landscape ecology?