1. Island Biogeography Theory
Equilibrium theory of island biogeography = explains how species come to be distributed among oceanic islands
Also applies to “habitat islands” – patches of one habitat type isolated within a “sea” of others
Explains how the number of species on an island results from an equilibrium between immigration and extirpation
Predicts an island’s species richness based on the island’s size and distance from the mainland

2. Species richness results from island size and distance
Fewer species colonize an island far from the mainland
Large islands have higher immigration rates
Large islands have lower extinction rates

3. The species-area curve
Large islands contain more species than small islands
They are easier to find and have lower extinction rates
They possess more habitats

4. Small “islands” of forest rapidly lose species
Forests are fragmented by roads and logging
Small forest fragments lose diversity fastest
Starting with large species
Fragmentation is one of the prime threats to biodiversity

5. General principles of island colonization:
1) The closer the island to another land mass, the higher the probability of colonization.  2) The older the island, the more likely it will be colonized.  3) The larger the island, the more species are likely to be established.  4) Geographic isolation reduces gene flow between populations.  5) Over time, colonial populations become genetically divergent from their parent population due to natural selection, mutation, and/or genetic drift.