RT info:eu-repo/semantics/article
T1 The island immaturity - speciation pulse model of island evolution: an alternative to the ‘‘diversity begets diversity’’ model
A1 Whittaker, Robert J.
A1 Ladle, Richard J.
A1 Araújo, Miguel B.
A1 Fernández-Palacios, José María
A1 Delgado, Juan Domingo
A1 Arévalo, José Ramón
K1 IISP model
K1 Canary Islands
K1 island evolution
K1 Islas Canarias
K1 evolución insular
AB Islands have long provided model systems in whichecologists and evolutionary biologists have developed,tested and refined models for species diversity(Whittaker and Ferna´ndez-Palacios 2007). In two recentpapers, Emerson and Kolm (2005a, b) have presentedand discussed multiple regression analyses from twooceanic archipelagos, the Canaries and Hawaii, demonstratingfor plants and arthropods that islands of greaterspecies richness also have higher proportions of singleisland endemics (SIEs). They claim this as evidence thathigher species richness of a taxon drives higher rates ofdiversification in that taxon, i.e. that ‘‘diversity begetsdiversity’’. Their analysis is interesting, but given that it isan analysis of proportions of SIEs not rate of speciesproduction, it is ultimately inconclusive as to mechanismsleading to the relationship. It might tell us,as inferred by Emerson and Kolm (2005a, b), thathigh species richness creates the conditions for high ratesof speciation through: 1) competitive interactions,2) genetic drift due to small population sizes, and3) greater community structural complexity. But it couldalso be that the relationship is a by-product of circumstancesnot adequately captured in their analyses.Herein, we develop an alternative model, positingthat the opportunities for speciation have a broadlypredictable relationship to the life cycle of oceanicislands. We term our model the island immaturity  speciation pulse (IISP) model of island evolution.Intrinsic to this model is that opportunity drivesspeciation rate and that opportunity is greatest at arelatively early stage of an island’s life cycle, whenintrinsic carrying capacity exceeds species richness by thegreatest margin, i.e. when there is greatest ‘‘vacant nichespace’’. As islands mature, both richness and endemismincrease in tandem, but as islands decline in their oldage, opportunities for speciation diminish, in tandemwith a reduced carrying capacity (and reduced numbersof SIEs). Our argument is that the mechanismsidentified by Emerson and Kolm (2005a, b), whilsteach having a role in island evolution, make for anincomplete set of key island mechanisms and that inparticular they neglect the likely importance of competitiverelease early in the life cycle of an island, and of thesubsequent decline in carrying capacity, for the proportionsof single island endemics (see Peck et al. 1999).In setting out the IISP model, we describe theobservations on which it is based, and then examinewhat we expect in terms of critical rates, and emergentpatterns of SIEs, comparing our model with that putforward by Emerson and Kolm (2005a, b). Weillustrate our model with reference to data for thearthropods and plants of the Canary Islands (cf.Emerson and Kolm 2005a).
PB Oikos Editorial Office
YR 2007
FD 2007
LK http://riull.ull.es/xmlui/handle/915/18481
UL http://riull.ull.es/xmlui/handle/915/18481
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DS Repositorio institucional de la Universidad de La Laguna
RD 24-abr-2024