Saturday, July 19, 2008

A new look at oceanic island biogeography

Oceanic islands have long fascinated biogeographers and ecologists, and indeed their study has played an important role in our understanding of the distribution and evolutionary origins of species. However, it is also acknowledged that the existing body of island biogeographical theory has been less successful and is less complete when applied to oceanic island systems operating on evolutionary timescales than where applied to less isolated archipelagos. This has led to repeated calls for the development of new theories of oceanic island biogeography, re-unifying ecological and evolutionary biogeography.
In a study recently published in the Journal of Biogeography, Robert Whittaker, Kostas Triantis and Richard Ladle present what they term a general dynamic model (GDM) of oceanic island biogeography. Their aim is to provide a general explanation of oceanic island biodiversity patterns through describing the relationships between fundamental biogeographical processes – speciation, immigration, extinction – through time and in relation to the island life-cycle. The argument is built on combining three premises: (1) that emergent properties of island biotas are a function of rates of immigration, speciation and extinction, (2) that evolutionary dynamics predominate in large, remote islands, and (3) that oceanic islands are relatively short-lived landmasses showing a characteristic humped trend in carrying capacity over their life span. Based on these premises, Whittaker and his colleagues derived several new predictions concerning the emergent properties of oceanic island biotas.
The authors go on to evaluate these expectations principally by means of simple analyses of proportions of endemics on each island within several oceanic archipelagos, finding broad support for the model, while noting that “The GDM is a deliberately simplified representation of diversity dynamics on oceanic islands”. As such it necessarily glosses over important details, but offers the promise of a more integrative and dynamic island biogeographical theory, and a framework for a renewed effort to integrate ecological and evolutionary approaches to the study of island biotas.

Source paper: Whittaker, R.J., Triantis, K.A. & Ladle, R.J. (2008) A general dynamic theory of oceanic island biogeography. Journal of Biogeography, 35, 977–994.

Source of article: Journal of Biogeography highlighted papers

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