Island Biogeography Part I

Geographic Ecology

Search for patterns of animals and plant life that can be put on a map

Study of community ecology patterns at large spatial scale 

Who travelled through Spanish empire (June 5th, 1799)

• Alexander Von Humboldt (father of geography and geographic ecology) 

• Aime Bonpland

Expedition (Humboldt and Bonplaned)

Travelled from North to South America, they climbed the highest mountains of the Andes

• Recorded altitudinal distributions of plants and animals

• Organized observations based on climate and distributional patterns

Von Humboldts Contribution

1) Introduced idea of mapping species distributions

2) Idea of large-scale trends/patterns in nature

3) Understanding connections/relationships between species distributions/abiotic factors

4) Inspired others (Darwin/Wallace) to be naturalists and doc the presence/absence of species.

Reasons why islands are important from ecological conservation and biogeographical point of view

• First biologist studied island (Developed principles important in ecology and evolutionary biology) 

• Very fast rates of speciation and extinction 

• Little or no gene flow to dilute the effect of selection and mutation causing a very high level of endemism

• Species that experience ecological release, leading to expanded niches, increased densities compared to their mainland relatives

• Extraordinary and versatile pollinators and seed dispersers that assume the roles of their numerous absent counterparts. 

Ecological Naive Species

Species that went extinct due to human activities. (eg, flightless insects, birds, giant rodents and dwarfed elephants, other endemic species) 

Oceanic islands are hotspots of biodiversity (high levels of endemism) 

Extinctions in Insular Systems

Anthropogenic activities played significant role in recent extinctions on islands. Activities include 

• habitat destruction 

• Overexploitation 

• Introduction 

Island Gigantism (phenomenon) 

• Reduced Predation 

• Enhanced Competition 

• Resource Release 

Island Dwarfism (phenomenon)

• Limited food resources

• Smaller habitat space

• Reduced predation needs 

Flightlessness and reduction dispersal ability on islands

Flightless birds and insects are relatively common on many oceanic islands (New Zealand). Before human colonization, most Pacific islands were inhabited by flightless rail species.

Oceanic Island (Description)

Situated on an oceanic plate, never part of continent.

Continental (land-bridge) Island

Once connected to a continent, sitting on the continental shelf, possibly formed as continents shifted. 

Fragmented Habitats

Results from human activities (eg., habitat fragmentation, deforestation, urbanization), creating isolated patches.

The Island Biogeography Theory (3 trends) (MacArthur and Wilson 1967)

1) Tendency of # of species to increase with island area

2) Species-Area relationship

3) Tendency or # or species to decrease with island isolation (species-isolation relationships)

Species-Area Relationship

Has equations

Species-isolation Relationship

More isolated (distant) islands contains few species than nearby islands

Species Turnover 

Equilibrium is dynamic with immigration and extinction opposing each other, ensuring stable species richness despite turnover 

Species Turnover (example)

Island of Krakatau

• volcano exploded in 1883

• Various remnants

• The world temp decreased by 1 °C for months. 

• Broke Island in 3 places 

Extinction determined by 

Size of island 

Immigration determined by

Distance (isolation) from source populations or the mainland.