Islands are simplified ecosystems that provide natural scientists with multiple, discrete units to study and upon which to base more general biogeographical, ecological and evolutionary theory. Island biogeographical theory has provided a framework for estimating species losses and to guide conservation management as continental landscapes become increasingly fragmented into ‘habitat islands’.

Keywords: adaptive radiation; biogeography; ecological assembly; equilibrium theory; taxon cycle

Figure 1.

The role of spatial and temporal scale in defining ecological and evolutionary processes. (1) Range and lifetime of an individual; (2) population scale operating in ecological time (e.g. competition); (3) population scale operating over evolutionary time (e.g. differentiation); (4) species scale (e.g. adaptive radiation). (Redrawn from Haila, ).

Figure 2.

Conceptual model depicting the relationship between geographical variables and evolutionary process (from Whittaker, ). The model indicates a trend from micro‐ to macro‐evolutionary changes as island isolation and area increase: large, distant islands are most disharmonic and possess most vacant niche space, perfect platforms for spectacular radiations; tiny islands, even if isolated, fail to provide for the persistence of large populations and complex ecosystems, and thus feature impoverished biotas of widespread species; large near‐mainland islands typically contain a full balance of species and lack the long‐term isolation that favours lineage radiation. For terms, see text, apart from ‘anagenesis’, which refers to speciation with little or no radiation, most prevalent on single, isolated islands in contrast to the radiations more prevalent on archipelagos.

Figure 3.

The equilibrium theory of island biogeography (ETIB) proposed by MacArthur and Wilson showing the relationship of distance from an island and source area on immigration (I), island area on extinction (E), and the intersection of both at an equilibrial point to produce a turnover rate (T) at a predictable species number (S). The roughly triangular area bounded by the darkened lines to the left of the turnover intersection point delimits the turnover rates and species numbers theoretically possible before equilibrium is reached (fl, far large; ns, near small).



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Further Reading

Brown JH and Lomolino MV (1998) Biogeography, 2nd edn. Sunderland, MA: Sinauer.

Darwin C (1845) Voyage of the Beagle. London: Murray.

Global Ecology and Biogeography (2000) 9(1) 1–92. [Island Biogeography Special Issue.]

Grant PR (ed.) (1998) Evolution on Islands. Oxford: Oxford University Press.

Grant PR and Weiner J (1999) Ecology and Evolution of Darwin's Finches. Princeton, NJ: Princeton University Press.

Hubbell SP (2001) The Unified Neutral Theory of Biodiversity and Biogeography. Princeton, NJ: Princeton University Press.

Quamman D (1996) Song of the Dodo; Island Biogeography in an Age of Extinctions. London: Hutchinson.

Weiher E and Keddy P (eds) (1999) Ecological Assembly Rules: Perspectives, Advances, Retreats. Cambridge: Cambridge University Press.

Williamson M (1992) Island Populations. Oxford: Oxford University Press.

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Henderson, Scott J, and Whittaker, Robert J(Mar 2003) Islands. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0003234]