Island biogeography

Definition

A body of ecological theory and empirical study examining how isolation and area govern species richness, colonization, and extinction in discrete habitat patches. Originally formulated for oceanic islands, the framework now applies to any isolated ecosystem—mountain peaks, forest fragments, urban habitat patches, or caves—where dispersal limitation and local extinction create distinctive community dynamics. The equilibrium model predicts that species number reflects a balance between immigration rates (decreasing with isolation) and extinction rates (decreasing with area).

Etymology

From Latin insula (island) + Greek bios (life) + graphein (to write); coined by Robert H. MacArthur and E. O. Wilson in their 1967 monograph "The Theory of Island Biogeography."

Example

A study of carabid beetles in forest fragments of varying sizes found that smaller patches supported fewer species, with the most isolated fragments showing delayed recolonization after local extinctions—consistent with island biogeography predictions.

Synonyms

• insular biogeography

Related Terms

• species–area relationship
• metapopulation
• habitat fragmentation
• edge effect
• beta diversity
• rescue effect
• target effect

Usage Notes

The term now extends well beyond literal islands; specialists distinguish between true insular systems (surrounded by uninhabitable matrix) and habitat islands (surrounded by modified but not necessarily lethal matrix). Equilibrium predictions assume stable environmental conditions and ignore evolutionary time; deviations are common in dynamic or anthropogenic landscapes. Contrast with mainland–island metapopulation models, which emphasize source–sink dynamics rather than mutual colonization–extinction balance.