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Islands as biological substrates: classification of the biological assemblage components and the physical island types

Ali, Jason R.
Journal of biogeography 2017 v.44 no.5 pp. 984-994
ancestry, biogeography, islands, ontogeny, subsidence, tectonics
AIM: Biological suites on marine islands attract the attention of many researchers because their natural seclusion enables a variety of key processes to be studied in considerable detail. The present‐day classification of marine‐island biotic systems is based largely on 19th Century ideas, specifically those of Darwin and Wallace. However, along a number of fronts, knowledge has advanced dramatically, particularly regarding the dynamic ‘solid’ Earth (plate tectonics, ocean‐floor thermal‐cooling subsidence, mantle‐plume hotspots, etc.), as well as the behaviour of the planet's liquid and gaseous envelopes, today and in the geological past. This manuscript serves as an introduction to a series of articles aimed at providing the biological/biogeographical community with an overview of the current understanding of the physical settings of the marine islands, that is, the substrates upon which the biotas accumulate and develop. LOCATION: Global. RESULTS: I propose separate classification systems for the biotic assemblage components and the physical island types to replace the current mixed scheme of recent continental, ancient continental and oceanic. The lifeforms can be assigned to one of four classes reflecting how an organism's founder ancestors colonized an island: recent land bridge, recent ice‐sheet, overwater dispersed and deep‐time vicariant (an island may host two or more of these types). The nomenclature for the islands reflects their geo‐physical setting and has the advantage of indicating the ontogenetic path the landmass is on. In turn, this may feed back into the way the hosted biology is viewed. Four major categories are recognized: continental, island arc, composite terrane and mantle‐plume hotspot, plus a handful of left‐overs. These groups can be further split into between three and nine types. MAIN CONCLUSION: Separating the classifications of the island biotic assemblage components and the physical island varieties (of which there are many sorts) makes it possible to assign all islands and their biotas unambiguously. It thus provides an appreciably more nuanced scheme than Wallace's threefold system.