Raia Pasquale, Meiri Shai
Università degli Studi del Molise, Dipartimento di Scienze e Tecnologie per l'Ambiente e il Territorio, Via Mazzini 8, 86170 Isernia, Italy.
Evolution. 2006 Aug;60(8):1731-42.
The island rule is the phenomenon of the miniaturization of large animals and the gigantism of small animals on islands, with mammals providing the classic case studies. Several explanations for this pattern have been suggested, and departures from the predictions of this rule are common among mammals of differing body size, trophic habits, and phylogenetic affinities. Here we offer a new explanation for the evolution of body size of large insular mammals, using evidence from both living and fossil island faunal assemblages. We demonstrate that the extent of dwarfism in ungulates depends on the existence of competitors and, to a lesser extent, on the presence of predators. In contrast, competition and predation have little or no effect on insular carnivore body size, which is influenced by the nature of the resource base. We suggest dwarfism in large herbivores is an outcome of the fitness increase resulting from the acceleration of reproduction in low-mortality environments. Carnivore size is dependent on the abundance and size of their prey. Size evolution of large mammals in different trophic levels has different underlying mechanisms, resulting in different patterns. Absolute body size may be only an indirect predictor of size evolution, with ecological interactions playing a major role.
岛屿法则是指岛屿上大型动物小型化和小型动物巨型化的现象，哺乳动物提供了典型的案例研究。针对这种模式已经提出了几种解释，而且在不同体型、食性习惯和系统发育亲缘关系的哺乳动物中，与该法则预测的偏差很常见。在此，我们利用来自现存和化石岛屿动物群组合的证据，对大型岛屿哺乳动物的体型进化提出一种新的解释。我们证明，有蹄类动物的侏儒化程度取决于竞争者的存在，在较小程度上还取决于捕食者的存在。相比之下，竞争和捕食对岛屿食肉动物的体型几乎没有影响，其体型受资源基础性质的影响。我们认为，大型食草动物的侏儒化是低死亡率环境中繁殖加速导致适应性增加的结果。食肉动物的体型取决于其猎物的数量和大小。不同营养级别的大型哺乳动物的体型进化有不同的潜在机制，从而导致不同的模式。绝对体型可能只是体型进化的一个间接预测指标，生态相互作用起着主要作用。
