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Article Dans Une Revue Revue d'Écologie Année : 2007

The biogeography of large islands, or how does the size of the ecological theater affect the evolutionary play

Résumé

We compare selected aspects of the biotas of long-isolated islands ranging in size from Réunion to early Pliocene South America, focusing on Madagascar, New Zealand, New Caledonia and the Hawaiian Islands. Although Madagascar and New Zealand were joined to larger land masses less than 90 million years ago, their biotas are overwhelmingly dominated by descendants of colonists from overseas. The size of a long-isolated land mass decisively infl uences major features of its ecosystem. On smaller islands, extinction is more likely, colonization is rarer, and there are fewer opportunities for diversifi cation. The largest herbivores and the largest carnivores are smaller on smaller islands. Reduced diversity, lower predation pressure and diminished evolutionary innovation reduce the severity of competition on smaller islands: their plants are less well defended against vertebrate herbivores, and their primary productivity is lower, while their animals are longer-lived, less fecund, and have lower basal metabolism than mainland ecological counterparts. Herbivores are most likely to evolve convergently with counterparts on other land masses with predators of similar size and/or effi ciency. Thus sloth lemurs converged on tree sloths, Megaladapis on koalas, and moa-nalos on moas and elephant birds. The degree of an island's isolation also affects its ecosystem's characteristics. More isolated islands receive fewer immigrants, so diversity is lower on more isolated islands, especially small islands with high risks of extinction. Fewer mainland immigrants, whose effi ciency was tested against a variety of competitors and well-defended prey, reach more isolated islands, so competition is less intense on these islands, and these islands' predators are less effi cient. Smaller size and greater isolation therefore make a land mass more invasible. Islands with the fewest predators and the slowest pace of life are most likely to be catastrophically disrupted by mainland invaders. All these phenomena have analogues in human economies. As a rule, economies with higher total production support more intense competition, more innovation, a greater diversity of occupations, a faster pace of life, and greater productivity per capita.
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hal-00283373 , version 1 (14-12-2010)

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  • HAL Id : hal-00283373 , version 1

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Egbert Giles Jr Leigh, Annette Hladik, Claude Marcel Hladik, Alison Jolly. The biogeography of large islands, or how does the size of the ecological theater affect the evolutionary play. Revue d'Écologie, 2007, 62, pp.105-168. ⟨hal-00283373⟩
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