The island rule: made to be broken?

Abstract

The island rule is a hypothesis whereby small mammals evolve larger size on islands while large insular mammals dwarf. The rule is believed to emanate from small mammals growing larger to control more resources and enhance metabolic efficiency, while large mammals evolve smaller size to reduce resource requirements and increase reproductive output. We show that there is no evidence for the existence of the island rule when phylogenetic comparative methods are applied to a large, high-quality dataset. Rather, there are just a few clade-specific patterns: carnivores; heteromyid rodents; and artiodactyls typically evolve smaller size on islands whereas murid rodents usually grow larger. The island rule is probably an artefact of comparing distantly related groups showing clade-specific responses to insularity. Instead of a rule, size evolution on islands is likely to be governed by the biotic and abiotic characteristics of different islands, the biology of the species in question and contingency.

How do seemingly non-vagile clades accomplish trans-marine dispersal? Trait and dispersal evolution in the landfowl (Aves: Galliformes)

“…This 'partridge' morphotype has evolved multiple times across Phasianoidea, and is characteristic of genera including Perdix, Francolinus, Pternistis, Arborophila and others [28,34]. Evolution of body size has been suggested as an adaptation in populations following insular colonization [54][55][56], although whether or not it is a predictable, general pattern remains controversial [57,58]. In theory, island gigantism (i.e.…”

Unravelling the determinants of insular body size shifts

“…However, this generalization may be an oversimplification of a weak overall pattern [3] where exceptions abound [4]. For example, insular size shifts appear to be concentrated in a few key clades [5], and the magnitude of size shifts within a single species can vary among islands [6].…”

“…Analyses combining multiple explanatory variables are rare and often limited to specific clades [13] and sets of islands [14]. Phylogenetic analyses, which have the potential to elucidate underlying evolutionary constraints, are also rare (but see references [5,13,15]). Here, we assemble a dataset, including key climatic, geographical and biological data for 721 islands and 184 mammal species along with their insular size shifts.…”

Island Species Richness Increases with Habitat Diversity

“…Although it is true that biases are common in the data used for ecological research (Hortal et al 2007(Hortal et al , 2008a, the publication process per se is unlikely to be strongly biased against results that contradict mainstream ecological theory (see Palmer 1999;Meiri et al 2004). In fact, negative results in community ecology are often viewed as novel and exciting and may therefore be more likely to be published (Purvis et al 2003;Meiri et al 2008). Even MacArthur and Wilson's (1967) theory was severely criticized from almost the time it was presented (see Sauer 1969;Gilbert 1980;Whittaker and Fernández-Palacios 2007, table 6.1), starting a long process of criticism and updates of the mainstream theory that continues today (e.g., Bellemain and Ricklefs 2008;Whittaker et al 2008;Losos andRicklefs 2009a, 2009b).…”