The ‘Island Rule’ Acting on Anuran Populations (Bufonidae: Rhinella ornata) of the Southern Hemisphere

Abstract

Darwin and Wallace, in the mid-nineteenth century, were the first to document examples of natural selection acting on island dwellers. A century later a pattern of morphological differences among organisms on islands was coined the 'island rule', which states that on islands species with small individuals tend toward gigantism and large individuals tend toward dwarfism. Selective pressures such as limited resources and increased intraspecific competition modulate the size of organisms in these environments. Of the several works that have tested vertebrates for adherence to the island rule only two have addressed amphibians. This work is the third record of body size variation of island amphibian populations, and the first for the Southern Hemisphere. The islands investigated were once continuous with mainland, and now are isolated as a result of sea level fluctuations that took place in the Pleistocene and Holocene. This study compared morphometric variation in populations of Rhinella ornata (Bufonidae) occurring on three islands of the Costa Verde to populations on five continental areas in Rio de Janeiro, Brazil. We measured 18 morphometric variables of 177 individuals. There was a shift toward smaller body size (dwarfism) in two of the three island populations studied. We attribute this general pattern to geographic factors, verifying the expression of the island rule in tropical frogs populations (insular dwarfism) operating inversely in relation to those of temperate environments (island gigantism).Abstract in Portuguese is available in the online version of this article.

The island rule in the Brazilian frog Phyllodytes luteolus (Anura: Hylidae): incipient gigantism?

“…However, exceptions occur, such as Rhinella ornata (Spix, 1824) (larger on the mainland) in Rio de Janeiro, Brazil (MONTESINOS et al 2012). This difference between dwarfism and gigantism on islands and continents is probably due to the complex interaction between food, space and predation (WU et al 2006), but may also be explained by the size range of the animals in question.…”

The island rule: An assessment of biases and research trends

“…Apart from studies on the island rule that focus on mammals (e.g. Bromham & Cardillo, ; Lyras, Van Der Geer, & Rook, ; Meiri, Dayan, & Simberloff, ; Palombo, ; Rozzi & Palombo, ), researchers have also applied and tested this general hypothesis for a number of other taxonomic groups, including amphibians (Montesinos, Silva, & Carvalho, ), birds (e.g. Boyer & Jetz, ; Clegg & Owens, ), dinosaurs (Benton et al., ), fish (Herczeg, Gonda, & Merilä, ), insects (e.g.…”

“…Many studies, however, report changes in body size for single species or populations and then relate their observations to the island rule. Examples are found across taxa: insects (Hoch et al, 2014;Pizzo, Mazzone, Rolando, & Palestrini, 2011), fishes (Herczeg et al, 2009), amphibians (Montesinos et al, 2012), dinosaurs (e.g. Benton et al, 2010), birds (Mathys & Lockwood, 2009), and a number of mammalian species including mice (Michaux, de Bellocq, Sar a, & Morand, 2002), deer (Simard, Côt e, Weladji, & Huot, 2008) and marten (L opez-Mart ın, Ruiz-Olmo, & Padr o, 2006).…”

One step beyond a broad molecular phylogenetic analysis: Species delimitation of Adenomera marmorata Steindachner, 1867 (Anura: Leptodactylidae)

“…On the other hand, specimens of A. marmoratafrom Alcatrazes Island (CCS J) are much larger than specimens from other populations (male minimum SVL 25.6 mm, n = 1, female minimum SVL 25.7 mm, n = 4; other mainland populations male maximum SVL 22.4, n = 37, female maximum SVL = 23.4 mm, n = 24). Vertebrate gigantism on islands has massively been reported in the literature ( [78][79][80]). Nevertheless, Rebouças et al [80] found opposite results, (i.e.…”