Make your own free website on Tripod.com
Restoration Ecology - Week 3

Island Biogeography and Habitat Fragmentation

I. Specices-Area Reltionships
A. Observations - big areas generally have more species than small areas. Why?
B. Model
1. S = CAZ (Overhead #1)
where S = number of species present
A = area of island or reserve
C = constant
z = an exponent whose value varies between 0.24 and 0.33 on islands and 0.12 to 0.17 on the mainland
2. log S = log C + zlogA (Overhead #2)

II. Island Biogeography
A. Theory proposed by McArthur and Wilson (1967) based on work by Preston (1962)
B. Several assumptions (Overhead #3)
1. Species diversity is a balance between immigration and extinction
2. Immigration rates decrease as the number of species increases
3. Immigration rates are higher on near islands than on far islands
4. Immigration rates are higher on large islands than on small islands
5. Extinction rates are higher on small islands than on large islands
C. Equilibrium model (Overhead #4)
1. S = I - E
D. Equilibrium model - near islands and far islands (Overhead #5)
E. Equilibrium model - large islands and small islands (Overhead #6)

III. Species-Area Examples
A. Orchids in the Bahama Islands (Overhead #7 )
B. Birds on Great Basins Mountain Tops (Overhead #8 )
C. Mammals on Great Basin Mountain Tops (Overhead #9)
D. Plants on the Galapagos Islands (Overhead #10)
E. Herps in the West Indies (Overhead #11)
F. Unknown species in North Florida (Overhead #12 )

IV. Effects of Habitat Fragmentation
A. Habitat fragmentation ranks among the most serious causes of the erosion of biological diversity (Harris 1992 in Fiedler and Jain)
B. Fragmentation occurs when a large expanse of habitat is transformend into a number of smaller patches of smaller total area, isolated froom each other by a matrix of habitats unlike the original (Wilcove et al. In M. Soule 1986)
C. 90/50 rule (Overhead #13)
D. Theoretical example (Overhead #14)
E. Fragmentation
1. Veracruz Mexico (Overhead #15)
2. Cadiz Township, WI (Overhead #16)
3. Edge Effects (Overhead #17)
4. Preserve Designs (Overhead #18)
V. Island Biogeography - Relevance to Restoration
A. Number of species a restored habitat can support is proportional to its area
B. Reestablishment becomes more difficult as the number of species increases
C. Isolated site require more effort
D. Small sites require more unit effort
E. Small sites require more post-restoration management
VI. Restoration - Relevance to Island Biogeography
A. Restoration can do the following
1. Increase reserve size (increase e, decrease e)
2. Decrease distances between reserves (increase I, decrease e)
a. archipelagos
b. corridors
3. Minimize edge effects (decrease E)
a. Make "rounder"
b. Create buffer zones
SUMMARY
A. Many natural areas and restored sites are islands
B. Number of species a restored habitat can support is proportional to its area
C. Restoration should maximize I and minimize E