Island biogeography explained
The classic model proposes that immigration tends to add species and local extinction removes them, with island isolation affecting arrival and area affecting persistence. It predicts tendencies and turnover around a dynamic richness, not an exact permanent species list for every island or habitat fragment.
Scope: A worldwide introduction to equilibrium island-biogeography theory and its extensions to oceanic islands and habitat fragments. Area and isolation are central predictors, but habitat diversity, matrix permeability, disturbance, evolutionary history, species traits, and human transport also influence richness and turnover. · Last updated
The equilibrium is dynamic
In the classic model, immigration falls as more of the regional species pool arrives, while extinction rises as an island accumulates species with smaller average populations and more interactions. Where the rates cross is an expected richness. Species can continue replacing one another around that value, so equilibrium does not mean ecological stillness or a fixed roster. [1][2]
Area and isolation change the odds
Large islands generally offer more habitat and can support larger populations, reducing some extinction risks. Near islands are usually reached by more dispersers than remote ones. The famous species–area and isolation patterns are statistical, however: a small diverse island can exceed a larger uniform one, and strong fliers, windborne spores, rafting reptiles, and human-carried organisms experience distance very differently. [1][3]
Evolution enters on longer timescales
Remote islands may receive few colonists yet generate endemic lineages as populations diverge and diversify. Island age, geological change, climate, and extinction determine how much evolutionary history remains visible. Models that include speciation can better describe oceanic archipelagos, but even those models simplify changing area, connectivity, and environmental conditions through time. [1][2]
Habitat fragments are island-like, not identical
Forest remnants, ponds, and mountaintops can be analyzed as patches surrounded by a contrasting matrix, but that matrix is rarely equivalent to ocean. Some species cross farms or cities; others do not, and edges alter light, wind, predators, and vegetation. Island theory helps frame conservation questions about patch size and connectivity, while local habitat quality and movement data are needed before treating a reserve as a sealed island. [3][4]
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Where this guide comes from
Source-checked editorial guide. Last updated . This guide teaches identification and field skills; it is not a substitute for expert verification when it matters.
- Ecology and evolution — A niche-based theory of island biogeography ↗
- Proceedings of the National Academy of Sciences of the United States of America — Immigration and extinction probabilities for individual species: relation to incidence functions and species colonization curves ↗
- The Quarterly review of biology — The reticulating phylogeny of island biogeography theory ↗
- USDA Forest Service — Island biogeography and fragmented landscapes ↗
