2.3 Island Biogeography

Island Biogeography Basics

The theory of island biogeography explains species richness on islands (or isolated habitats like lakes, parks) based on island size and distance from the mainland. Larger islands support more species because they have more resources and habitat diversity. Islands closer to the mainland receive more immigration of new species, increasing colonization rates.

Equilibrium of Species Richness

Species number on an island reaches equilibrium when the immigration rate equals the extinction rate. Small, far islands reach equilibrium with fewer species; large, near islands reach equilibrium with more species. This dynamic balance explains why isolated ecosystems (islands, fragmented habitats) tend to have lower biodiversity than similar mainland areas.

Applications to Conservation

Habitat fragmentation creates 'islands' of habitat surrounded by human development. Understanding island biogeography helps conservationists design habitat corridors and larger, connected reserves to maintain higher immigration rates and reduce extinction risk, preserving greater biodiversity in fragmented ecosystems.

Key terms

Theory of island biogeography

Explains species richness on islands based on island size and distance from the mainland.

Immigration rate

The rate at which new species arrive and colonize an island.

Extinction rate (island biogeography)

The rate at which species on an island die out.

Equilibrium species richness

The stable number of species reached when immigration rate equals extinction rate.

Habitat corridor

A connective strip of habitat linking fragmented areas, increasing immigration and biodiversity.

Try an AP-style question

According to island biogeography, which island has the most species?

1. A large island close to the mainland
2. A small island far from the mainland
3. A small island close to the mainland
4. A large island far from the mainland