Island Biogeography

Island Biogeography

Island Biogeography

• Colonization - arrival

• float
• fly
• swim
• be carried
• wind (seeds, spores)

Surtsey (1963)

Plant colonization - Surtsey

Krakatau (1833)

Colonization - Krakatau

Characteristics of Island Species

• Good dispersal ability

• Flock loving animals

• Prefer fresh water, mangroves, secondary forest on the mainland

• High ecological flexibility

Maquire (Ecol. Monog. 33:161-185)

• Placed bowls of nutrient solution at various distances and heights from a pond.

• Some bowls increased, then decreased in one species as others moved in.

• The number of new species/unit time decreased with time. They finally reached an equilibrium state.

• Different bowls had different species assemblages.

MacArthur and Wilson

Enclosing the “island”

Simberloff - equilibrium

Size relationships

• If same distance from mainland, immigration should be the same

Small Islands - high turnover rate

• Microtus pennsylvanicus (meadow vole)

• Clethrionomys gapperi (red-backed vole)

• 12 red-backed voles introduced to Rock Island

• rapidly displaced meadow vole in small woodland
• population never > 30
• went extinct in 3 years

Inland Islands

• Mountain tops in New Guinea

Species/Area relationships

Nonequilibrium theory

• Suggested by Lawlor

• Non-flying mammals have not come to equilibrium on oceanic islands

Relationship to Distance

• Extinction is not likely to be affected by remoteness

MacArthur-Wilson model predictions

• Number of species should remain constant over time

• Some species should become extinct over time

• Extinctions balanced by immigrations

• Turnover rate of species should vary with island area and distance from a source of immigrants

Assembly rules

• Worked out by Jared Diamond

• Three sets of rules determining the species mix on an island

• Incidence functions
• Compatibility rules
• Combination rules

Incidence Functions

• Incidence functions place species into 3 groups:

• Species only on species rich islands.
• Tramps - on species rich islands and with lower probability on species poor islands.
• Super tramps - only on species poor islands.

Compatibility rules

• Built from mutually exclusive ranges of pairs of species.

• Certain closely related species cannot co-exist.

Combination rules

• Based on diffuse competition rather than direct.

• Prevents certain groups of species from co-existing.

• Calculates the probability of a given combination being found together on an island of a given size

• The only stochastic part is the order of arrival of the first colonists.

Example: Cuba