Island biogeography: lecture topics. Introduction to island communities: Empirical patterns of species diversity on islands MacArthur & Wilson Dynamic Theory of Island Biogeography Theory Tests Criticisms/problems Environmental application of island biographical theory: Conservation Biology.
Only four Resident landbird species, of which Cocos Finch shown here (used as example of ecological release = niche expansion in prior lecture)(Photos T.W. Sherry & T.K. Werner)
Next pattern: Species-area curve illustrates dependence of species richness on area. Example shown here for herpetofauna (reptiles & amphibians) of Greater Antilles and nearby smaller Caribbean islands
Z-values (slope in species-area curve) tend to be lower in groups that disperse well (such as birds, graph b) than in groups that show more effect of isolation (such as mammals, graph c)
Final pattern: Isolation effect, shown by fewer species on isolated islands, in species-area curve for birds of warm ocean regions: red triangles represent isolated islands (>300 km from next largest land mass) (from Paul Slud)
Cocos Island, Costa Rica
Graphical model of one variation of MacArthur-Wilson Dynamic Theory of Island Biogeography
Both isolation (distance) effects on immigration, and island size (area) effects on extinction, combined into one model--showing different predicted equilibrium species richness values
Rate (immigration, extinction, turnover = T)
No. Species on Island
Result? Many animal species disappeared from forest fragments, especially rainforest interior species; big edge effects on trees & other species
Cocos Island: Vagrant, starving great blue heron (due to disharmonious-ness of fauna, harsh climate) would be unlikely to colonize successfully. Thus successful dispersal does not guarantee successful colonization.(Photo T.W. Sherry & T.K. Werner)
Relaxation effect: Number of species on continental islands decreases back towards MacArthur-Wilson equilibrium over time, from super-saturated condition when island formed by post-Pleistocene sea-level rise
Edge effect (perimeter)
Acknowledgements: Some illustrations for this lecture from R.E. Ricklefs. 2001. The Economy of Nature, 5th Edition. W.H. Freeman and Company, New York.