Island gigantism is a biological phenomenon in which the size of animals isolated on an island increases dramatically in comparison to their mainland relatives. Large mammalian carnivores are often absent on islands, due to their large range requirements and/or difficulties in over-water dispersal. In their absence, the ecological niches for large predators may be occupied by birds or reptiles, which can then grow to larger-than-normal size. For example, on prehistoric Gargano Island in the Miocene-Pliocene Mediterranean, on islands in the Caribbean like Cuba, and on Madagascar and New Zealand, some or all apex predators were birds like eagles, falcons and owls, including some of the largest known examples of these groups. However, birds and reptiles generally make less efficient large predators than advanced carnivorans. Since small size usually makes it easier for herbivores to escape or hide from predators, the decreased predation pressure on islands can allow them to grow larger. Small herbivores may also benefit from the absence of competition from missing types of large herbivores. Thus, island gigantism is an evolutionary trend resulting from the removal of constraints related to predation and/or competition. (In contrast, the complementary phenomenon of island dwarfing results from the imposition of constraints associated with the limited area and food supply available on islands.) 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.
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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 (both extinct)
Many rodents grow larger on islands, whereas lagomorphs, carnivores, proboscideans and artiodactyls usually become smaller.
- Giant rabbits (e.g. the Minorcan Giant Lagomorph) and shrews (e.g. the Corsican Giant Shrew) from Mediterranean islands (extinct)
- Carnivores
- The extinct Falkland Islands Wolf
- Primates
- The extinct giant lemur genera Archaeoindris, Palaeopropithecus and Megaladapis of Madagascar.
Birds
- Ratites
- The elephant bird, among the largest birds ever, formerly living on Madagascar (extinct)
- The extinct moa of New Zealand.
- Waterfowl
- Wildfowl
- Sylviornis neocaledoniae a huge extinct megapode-like bird from New Caledonia
- Some extinct Polynesian megapodes.
- Rails
- 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
- Haast's Eagle and Eyles' Harrier of New Zealand; the titan-hawk Titanohierax and giant-hawk Gigantohierax from the Caribbean; the giant buteonine hawk Buteogallus borrasi of Cuba (all now extinct).
- 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 (e.g. Tyto pollens) and Melanesia.
Reptiles
- Turtles
- Giant tortoises on the Seychelles, Galápagos Islands and formerly the Mascarenes
- Lizards
- The Komodo dragon and a similar (extinct) giant monitor lizard from Timor, examples of giant insular carnivores. Since islands tend to offer limited food and territory, their mammalian carnivores (if present) are usually smaller than continental ones. These cases involve ectothermic carnivores on islands too small to support much mammalian competition. (However, these lizards are not as large as their extinct Australian relative Megalania.)
- The 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
- Archosaurs
- The Cretaceous pterosaur Hatzegopteryx is one of the largest known pterosaur, and its remains come from Romania (which was an island in the Cretaceous)
Insects
- Madagascar hissing cockroach
- Saint Helena earwig
- Conant's Giant Nihoa Tree Cricket
- Lord Howe Island phasmid
- Giant weta of New Zealand
Flora
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
External links
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This page was last modified on 18 January 2010 at 18:52.
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