Island gigantism

Island gigantism is a biological phenomenon where the size of animals isolated on an island increases dramatically over generations. It is a form of natural selection in which bigger size provides a survival advantage (see Bergmann's Rule). Large size in herbivores usually makes it harder to escape or hide from predators, but on islands, these are often lacking. Thus, island gigantism is not an evolutionary trend due to fundamentally new parameters determining fitness (as in island dwarfing), but rather the removal of constraints. With the arrival of humans and associated predators (dogs, cats, rats, pigs), many giant island endemics have become extinct. As opposed to island dwarfing, island gigantism is found in most major vertebrate groups and in invertebrates.

Examples

Examples of island gigantism include:

Mammals

* Rodents
** Flores Giant Rats
** Giant hutias from the West Indies (extinct)
** Majorcan Giant Dormouse and Minorcan Giant Dormouse (extinct)Many rodents grow larger on islands, whereas lagomorphs, carnivores, proboscideans and artiodactyls usually become smaller.

*Primates
**the extinct giant lemur genera "Archaeoindris, Palaeopropithecus" and "Megaladapis" of Madagascar.

* Giant rabbits and shrews from Mediterranean islands (extinct)

Birds

*Ratites
**the elephant bird, among the largest birds ever, formerly living on Madagascar (extinct)
**the extinct moa of New Zealand.
*Waterfowl
**Moa-nalos, extinct giant ducks from Hawaii.
*Wildfowl
**"Sylviornis neocaledoniae" a huge extinct megapode-like bird from New Caledonia
**some extinct Polynesian megapodes.
*Rails
**the takahēs from New Zealand and other "Porphyrio" as well as many "Gallirallus" species from Melanesia and Polynesia and a few other Rallidae.
*Seabirds
**the extinct Spectacled Cormorant from Bering Island.
*Pigeons
**Dodo and Rodrigues Solitaire from the Mascarenes
**the extinct flightless Viti Levu Giant Pigeon.
*Birds of prey
** the extinct Haast's Eagle and Eyles' Harrier of New Zealand.
*Parrots
**the extinct Broad-billed Parrot from Mauritius, an undescribed huge extinct parrot from Easter Island, and the Kakapo of New Zealand.
*Owls
**Cuban "Ornimegalonyx" true owls and several "Tyto" barn owls from the Mediterranean, Caribbean and Melanesia.

Reptiles

*Turtles
**Giant tortoises on the Seychelles, Galápagos Islands and formerly the Mascarenes
*Lizards
**Komodo dragon and a similar (extinct) giant monitor lizard from Timor, rare examples of giant insular carnivores. Since islands tend to offer limited food and territory, their carnivores are usually smaller than continental ones. These cases may be unusual because they involve cold-blooded carnivores on islands too small to support much warm-blooded competition. (However, these lizards are not as large as their extinct Australian relative "Megalania".)
**Angel Island Chuckwalla ("Sauromalus hispidus") and the San Esteban Chuckwalla ("Sauromalus varius") of islands off Baja California
**"Leiolopisma mauritiana" and "Macroscincus coctei", two extinct skinks from Mauritius and Cape Verde, and the rare New Caledonian skink "Phoboscincus bocourti"
** the extinct Rodrigues giant day gecko and New Zealand giant gecko, and the extant New Caledonian giant gecko

Insects

*Madagascar hissing cockroach
*St. Helena Earwig
*Conant's Giant Nihoa Tree Cricket
*Lord Howe Island phasmid
*Giant weta of New Zealand

Flora

*Megaherb

In popular culture

The movie King Kong provides a fictional (and exaggerated) example of Island gigantism. The animals, bugs and plants found on Skull Island all present monstrous sizes.

See also

*Island dwarfing
*Island rule
*Deep-sea gigantism

External links

* [http://www.pbs.org/wgbh/nova/eden/giants.html PBS NOVA: Why Do Islands Breed Giants (And Sometimes Dwarfs)?]