Island Biogeography
MacArthur and Wilson's model of species richness as function of area and isolation.
The Theory of Island Biogeography was articulated by Robert H. MacArthur and Edward O. Wilson in their 1963 paper 'An Equilibrium Theory of Insular Zoogeography' (Evolution) and substantially elaborated in their 1967 monograph The Theory of Island Biogeography. The framework's central commitment is that species richness on islands reflects a dynamic equilibrium between immigration of new species (declining as more species are present) and extinction of resident species (increasing as more species are present), with equilibrium species number varying systematically with island area (larger islands have more species — the species-area relationship S = cA^z, where z is typically 0.2-0.3) and distance from mainland (closer islands have more species due to higher immigration rates). The empirical species-area relationship is one of the most robust patterns in ecology, observed across taxa, biogeographic regions, and spatial scales. MacArthur and Wilson's framework substantially shaped ecological thinking by replacing static-cataloging-of-species approaches with dynamic-equilibrium thinking, and the framework provided the conceptual foundation for modern conservation biology — particularly the design of nature reserves (single large or several small? — the SLOSS debate), the consequences of habitat fragmentation, and the prediction of extinction debt following habitat loss. Subsequent extensions include the unified neutral theory of biodiversity (Hubbell 2001, generalizing island biogeography to mainland communities), metapopulation theory (Levins, Hanski), and substantial work on island-mainland and inter-island species interactions. The framework has had enormous influence on conservation policy through species-area predictions of extinction following habitat loss, though specific predictions have varied in empirical validation.
Core components
- Dynamic equilibrium between immigration and extinction
- Species-area relationship S = cA^z (z typically 0.2-0.3)
- Distance effect on immigration rates
- Predictions about island species richness
- Application to habitat fragmentation and conservation
- SLOSS debate (Single Large Or Several Small) for reserve design
- Extinction debt following habitat loss
- Connection to metapopulation theory
- Foundation for unified neutral theory of biodiversity (Hubbell 2001)
- Substantial empirical support for species-area relationship across taxa and scales
Primary use case
Foundation of contemporary biogeography and macroecology; basis for substantial work in conservation biology and reserve design; reference framework for predicting extinction consequences of habitat loss; foundation for SLOSS debate and continuing reserve-design discussions; integration with metapopulation theory and landscape ecology; pedagogical foundation in ecology and conservation biology education; influence on contemporary biodiversity conservation policy; foundation for some commercial environmental-impact-assessment methodologies.
Common criticisms
- Predictions about specific species' extinction following habitat loss have varied in empirical validation — extinction debt sometimes follows predictions, sometimes shows substantially different dynamics
- the species-area relationship is robust but the underlying mechanisms (passive sampling vs ecologically meaningful equilibrium dynamics) remain contested
- habitat fragmentation effects depend substantially on matrix quality (the area between fragments) that simple island-mainland models don't address
- SLOSS debate remains unresolved — empirical evidence supports both single-large and several-small designs depending on context
- specific extinction predictions following habitat loss have been controversial — He and Hubbell 2011 argued species-area-based extinction projections are systematically overestimated
- commercial environmental-impact assessments often apply island-biogeography reasoning to mainland contexts where conditions differ substantially
- integration with phylogenetic and functional diversity frameworks has been productive but incomplete
- cross-taxonomic variation in species-area exponents complicates universal predictions
- the framework's mid-1960s formulation predates substantial subsequent ecological theory, requiring integration with metapopulation and landscape-ecology developments.
Lineage
- Siblings
- Predator-Prey Dynamics