Island gigantism

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The large Haast's eagle and moa from New Zealand (both extinct) Giant Haasts eagle attacking New Zealand moa.jpg
The large Haast's eagle and moa from New Zealand (both extinct)

Island gigantism or insular gigantism is a biological phenomenon in which the size of an animal isolated on an island increases dramatically in comparison to its mainland relatives. Island gigantism is one aspect of the more general "island effect" or "Foster's rule", which posits that when mainland animals colonize islands, small species tend to evolve larger bodies, and large species tend to evolve smaller bodies (insular dwarfism). With the arrival of humans and associated predators (dogs, cats, rats, pigs), many giant as well as other island endemics have become extinct. A similar size increase, as well as increased woodiness, has been observed in some insular plants.

Fosters rule

Foster's rule, also known as the island rule or the island effect, is an ecogeographical rule in evolutionary biology stating that members of a species get smaller or bigger depending on the resources available in the environment. For example, it is known that pygmy mammoths evolved from normal mammoths on small islands. Similar evolutionary paths have been observed in elephants, hippopotamuses, boas, sloths, deer and humans.

Insular dwarfism Form of phyletic dwarfism occurring on islands

Insular dwarfism, a form of phyletic dwarfism, is the process and condition of large animals evolving or having a reduced body size when their population's range is limited to a small environment, primarily islands. This natural process is distinct from the intentional creation of dwarf breeds, called dwarfing. This process has occurred many times throughout evolutionary history, with examples including dinosaurs, like Europasaurus, and modern animals such as elephants and their relatives. This process, and other "island genetics" artifacts, can occur not only on islands, but also in other situations where an ecosystem is isolated from external resources and breeding. This can include caves, desert oases, isolated valleys and isolated mountains. Insular dwarfism is one aspect of the more general "island effect" or "Foster's rule", which posits that when mainland animals colonize islands, small species tend to evolve larger bodies, and large species tend to evolve smaller bodies.

Extinction Termination of a taxon by the death of the last member

In biology, extinction is the termination of an organism or of a group of organisms (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "reappears" after a period of apparent absence.


Possible causes

Diagram displaying the change in size of weta species in two ecosystems. The size and population of wetas are affected by predation. Rats introduced on the mainland began to prey on wetas, reducing their population; wetas shrank in response. On an island isolated from predation, such as Little Barrier Island, wetas have a dense population and have grown to a massive size. Insular species of giant wetas are the only ones not facing extinction. As wetas grow over time, bird predation declines. Island Gigantism- A Growing Projection.png
Diagram displaying the change in size of weta species in two ecosystems. The size and population of wetas are affected by predation. Rats introduced on the mainland began to prey on wetas, reducing their population; wetas shrank in response. On an island isolated from predation, such as Little Barrier Island, wetas have a dense population and have grown to a massive size. Insular species of giant wetas are the only ones not facing extinction. As wetas grow over time, bird predation declines.

Large mammalian carnivores are often absent on islands because of insufficient range or difficulties in over-water dispersal. In their absence, the ecological niches for large predators may be occupied by birds, reptiles or smaller carnivorans, 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.

Oceanic dispersal is a type of biological dispersal that occurs when terrestrial organisms transfer from one land mass to another by way of a sea crossing. Often this occurs via large rafts of floating vegetation such as are sometimes seen floating down major rivers in the tropics and washing out to sea, occasionally with animals trapped on them. Dispersal via such a raft is sometimes referred to as a rafting event.

Ecological niche The fit of a species living under specific environmental conditions.

In ecology, a niche is the match of a species to a specific environmental condition. It describes how an organism or population responds to the distribution of resources and competitors and how it in turn alters those same factors. "The type and number of variables comprising the dimensions of an environmental niche vary from one species to another [and] the relative importance of particular environmental variables for a species may vary according to the geographic and biotic contexts".

The Miocene is the first geological epoch of the Neogene Period and extends from about 23.03 to 5.333 million years ago (Ma). The Miocene was named by Charles Lyell; its name comes from the Greek words μείων and καινός and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene is preceded by the Oligocene and is followed by the Pliocene.

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. [1] [lower-alpha 1] Small herbivores may also benefit from the absence of competition from missing types of large herbivores.

Herbivore animal anatomically and physiologically adapted to eating plant material

A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthparts adapted to rasping or grinding. Horses and other herbivores have wide flat teeth that are adapted to grinding grass, tree bark, and other tough plant material.

Benefits of large size that have been suggested for island tortoises include decreased vulnerability to scarcity of food and/or water, through ability to survive for longer intervals without them, or ability to travel longer distances to obtain them. Periods of such scarcity may be a greater threat on oceanic islands than on the mainland. [4]

Thus, island gigantism is usually an evolutionary trend resulting from the removal of constraints on the size of small animals related to predation and/or competition. [5] Such constraints can operate differently depending on the size of the animal, however; for example, while small herbivores may escape predation by hiding, large herbivores may deter predators by intimidation. As a result, the complementary phenomenon of island dwarfism can also result from the removal of constraints related to predation and/or competition on the size of large herbivores. [6] In contrast, insular dwarfism among predators more commonly results from the imposition of constraints associated with the limited prey resources available on islands. [6] As opposed to island dwarfism, island gigantism is found in most major vertebrate groups and in invertebrates.

Vertebrate subphylum of chordates

Vertebrates comprise all species of animals within the subphylum Vertebrata. Vertebrates represent the overwhelming majority of the phylum Chordata, with currently about 69,276 species described. Vertebrates include the jawless fishes and jawed vertebrates, which include the cartilaginous fishes and the bony fishes. The bony fishes in turn, cladistically speaking, also include the tetrapods, which include amphibians, reptiles, birds and mammals.

Territorialism may favor the evolution of island gigantism. A study on Anaho Island in Nevada determined that reptile species that were territorial tended to be larger on the island compared to the mainland, particularly in the smaller species. In territorial species, larger size makes individuals better able to compete to defend their territory. This gives additional impetus to evolution toward larger size in an insular population. [7]

Territory (animal) area a wild animal stays at and defends

In ethology, territory is the sociographical area that an animal of a particular species consistently defends against conspecifics. Animals that defend territories in this way are referred to as territorial.

Anaho Island island in the United States of America

Anaho Island is a rocky island in Pyramid Lake, and located on the Pyramid Lake Indian Reservation, Washoe County, in the U.S. state of Nevada.

A further means of establishing island gigantism may be a founder effect operative when larger members of a mainland population are superior in their ability to colonize islands. [8]

Island size plays a role in determining the extent of gigantism. Smaller islands generally accelerate the rate of evolution of changes in organism size, and organisms there evolve greater extremes in size. [9]


Examples of island gigantism include:


Many rodents grow larger on islands, whereas carnivores, proboscideans and artiodactyls usually become smaller.


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Corsican giant shrew Asoriculus corsicanus Corsica Extinct (before 500 BC) Red-toothed shrews
Balearic giant shrew Asoriculus hidalgo Majorca and Menorca Extinct
Sardinian giant shrew Asoriculus similis Sardinia Extinct
Deinogalerix koenigswaldi-Naturalis-PeterMaas.JPG
Deinogalerix spp. Gargano Island Extinct (Late Miocene) Moon rats


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Blunt-toothed giant hutia Amblyrhiza inundata Anguilla and Saint Martin Extinct (Pleistocene) Neotropical spiny rats
St Kilda field mouse (Apodemus sylvaticus hirtensis).png
St Kilda field mouse
Apodemus sylvaticus hirtensis St Kilda Least Concern Old World field mouse
Canariomys bravoi.jpg
Tenerife giant rat
Canariomys bravoi Tenerife Extinct (Late Pleistocene) African rufous-nosed rats
Canariomys tamarani fossils.JPG
Gran Canaria giant rat
Canariomys tamarani Gran Canaria Extinct (before AD 1500)
Larger Jamaican giant hutia Clidomys osborni Jamaica Extinct (Late Pleistocene) Neotropical spiny rats
Plate-toothed giant hutia Elasmodontomys obliquus Puerto Rico Extinct (c. 1 AD)
Formentera black-tailed garden dormouseEliomys quercinus ophiusae Formentera Rare [10] Garden dormouse
Minorcan giant dormouse Hypnomys mahonensis Menorca Extinct Leithiinae dormice
Majorcan giant dormouse
Hypnomys morpheus Majorca Extinct
Sicilian giant dormouse Leithia cartei Sicily Extinct
Maltese giant dormouseLeithia melitensis Malta Extinct
Gargano giant voles Mikrotia magna

M. maiuscula

M. parva
Gargano Island Extinct (Early Pliocene) Meadow voles
Flores giant rat
Papagamoys armandvillei Flores Near Threatened True rats
Sulawesi giant rat Paruromys dominator Sulawesi Least Concern
Channel Islands deer mice Peromyscus anyapahensis
P. nesodytes
northern Channel Islands of California Extinct Peromyscus maniculatus
Twisted-toothed mouse Quemisia gravis Hispaniola Extinct Neotropical spiny rats
Admiralty giant rat Rattus detentus Manus Island Unknown / Likely threatened [11] True rats
Congreso Island black rat population [12] Rattus rattusCongreso Island, one of the Chafarinas Islands Least Concern North African black rat
Arboreal giant hutia [13] Tainotherium valei Puerto Rico Extinct Neotropical spiny rats
Lesser Jamaica giant hutiaXaymaca fulvopulvis Jamaica Extinct


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Nuralagus NTy.jpg
Minorcan giant lagomorph
Nuralagus rex Menorca Extinct (Middle Pliocene)Alilepus (?)

Trischizolagus (?)
Prolagus imperialis Gargano Island Extinct Pikas
Sardinian pika
Prolagus sardus Corsica, Sardinia and Tavolara Extinct (c. AD 1800)


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Hispaniola monkey Antillothrix bernensis Hispaniola Extinct (before AD 1600) Titis
Archaeoindris fontoynonti.jpg
Gorilla lemur
Archaeoindris fontoynontiiCentral Madagascar Extinct (c. 350 BC) Galagos, pottos and lorises
Archaeolemur edwardsi.jpg
Baboon lemurs
Archaeolemur spp.

Hadropithecus spp.
Madagascar Extinct (before AD 1280)
Babakotia radofilai.jpg
Sloth lemurs
Babakotia spp.

Palaeopropithecus spp.
Western and Central MadagascarExtinct (c. AD 1500)
Haitian monkey Insulacebus toussaintianaSouthwestern Haiti Extinct Titis
Megaladapis grandidieri.jpg
Koala lemurs
Megaladapis edwardsi

M. grandidieri

M. madagascariensis
MadagascarExtinct (AD 1280-1420) Galagos, pottos and lorises
Paralouatta marianae skull.jpg
Cuban monkeys
Paralouatta marianae [14]

P. varonai [14]
Cuba Extinct (Pleistocene) Titis
Jamaican monkey Xenothrix mcgregori Jamaica Extinct


ExampleBinomial nameNative rangeCurrent statusContinental relatives
D2627 Megalenhydris.jpg
Sardinian giant otter
Megalenhydris barbaricina Sardinia Extinct (Late Pleistocene) Otters
Cryptoprocta Ferox.JPG
Cryptoprocta ferox Madagascar Vulnerable Mongooses
Giant fossa Cryptoprocta spelaea Madagascar Extinct


Stem birds

ExampleBinomial nameNative rangeCurrent statusContinental relatives
Balaur bondoc as avialan.jpg
B. bondoc Hateg Island Extinct (Late Cretaceous) Jeholornis [15]
Gargantuavis philoinos pelvis.JPG
G. philohinos Ibero-Armorican IslandExtinct (Late Cretaceous) Patagopteryx (?)


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Apteryx australis - Swedish Museum of Natural History - Stockholm, Sweden - DSC00615.JPG
Apteryx spp. New Zealand Variable Proapteryx [lower-alpha 2]
Aepyornis maximus.jpg
Larger elephant birds
Aepyornis hildebrandti

A. maximus

Vorombe titan
Madagascar Extinct (c. AD 1000)
Mullerornis agilis.jpg
Lesser elephant birds
Mullerornis spp. Madagascar Extinct (c. AD 1260)
Dinornithidae SIZE 01.png
Anomalopteryx didiformis

Dinornis spp.

Emeus crassus

Euryapteryx spp.

Megalapteryx didinus

Pachyornis spp.
New Zealand Extinct (before AD 1445) Tinamous


ExampleBinomial nameNative rangeCurrent statusContinental relatives
New Zealand musk duck Biziura delautouri New Zealand Extinct (after AD 1500)Australian musk duck
New Zealand geese
Cnemiornis calcitrans

C. gracilis
New Zealand Extinct Cape Barren goose
Garganornis ballmanni (reconstruction by Stefano Maugeri).jpg
G. ballmanni Gargano and Scontrone islandsExtinct (Late Miocene) Geese [17]
Turtle-jawed moa-nalo
Chelychelynechen quassus Kauai Extinct (c. AD 1000) Ducks
Moa Nalo Maui Nui.JPG
Small-billed moa-nalo
Ptaiochen pau Maui Extinct (c. AD 1000)
Moa Nalo Maui Nui.JPG
Maui Nui large-billed moa-nalo
Thambetochen chauliodous Maui Nui Extinct (c. AD 1000)
Thambetochen xanion.jpg
O'ahu moa-nalo
Thambetochen xanion O'ahu Extinct (c. AD 1000)
Giant swan Cygnus falconeri Sicily and Malta Extinct (Middle Pleistocene) Mute swan
Scarlett's duck Malacorhynchus scarletti New Zealand Extinct (after AD 1500) Pink-eared duck


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Pile-builder megapode Megapodius molistructor New Caledonia and Tonga Extinct (c. 1500 BC) Scrubfowl
Noble megapode Megavitiornis altirostris Fiji Extinct Galliformes
New Caledonian giant megapode
Sylviornis neocaledoniae New Caledonia and Isle of Pines Extinct


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Red rail
Aphanapteryx bonasia Mauritius Extinct (c. AD 1700) Rails
Aptornis BW.jpg
Aptornis defossor

A. otidiformis
New Zealand Extinct Trumpeters
Diaphorapteryx hawkinsi 1 1896.jpg
Hawkins's rail
Diaphanapteryx hawkinsi Chatham Islands Extinct (c. AD 1900) Rails
Fulica chathamensis 1 1896.jpg
Chatham coot
Fulica chathamensis Chatham Islands Extinct (after AD 1500) Coots
Fulica newtoni.jpg
Mascarene coot
Fulica newtonii Mauritius and Réunion Extinct (c. AD 1700) Eurasian coot
New Zealand coot Fulica prisca New Zealand Extinct (after AD 1280) Coots
Antillean cave rail Nesotrochis debooyi Puerto Rico and Virgin Islands Extinct Rails
Cuban cave rail Nesotrochis picapicensis Cuba Extinct
Haitian cave railNesotrochis steganinos Hispaniola Extinct
Porphyrio coerulescens.png
Réunion swamphen
Porphyrio coerulescens Plaine des Cafres, Réunion Extinct (c. AD 1730) Purple swamphens
Porphyrio hochstetteri -Tiritiri Matangi Island-8b-3c.jpg
South Island takahē
Porphyrio hochstetteri South Island, New Zealand Endangered Rails
North Island Takahe.jpg
North Island takahē
Porphyrio mantelli North Island, New Zealand Extinct (before AD 1900)


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Spectacled cormorant
Phalacrocorax perspicillatus Komandorski Islands Extinct (c. AD 1850) Double-crested cormorant


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Lapitiguana impensa.JPG
Viti Levu giant pigeon
Natunaornis gigoura Viti Levu, Fiji Extinct Crowned pigeons
Pezophaps solitaria.png
Rodrigues solitaire
Pezophaps solitaria Rodrigues Extinct (before AD 1778) Nicobar pigeon
Dodo 1.JPG
Raphus cucullatus Mauritius Extinct (c. AD 1662)

Birds of prey

ExampleBinomial nameNative rangeCurrent statusContinental relatives
Liko Cave golden eagleAquila chrysaetos simurgh Crete Extinct (Late Pleistocene) Golden eagle
Giant crab-hawk [18] Buteogallus borrasi Cuba Extinct Great black hawk
Jamaican caracara Caracara tellustris Jamaica Extinct Caracaras
Eyles's harrier Circus eylesi New Zealand Extinct (c. AD 1000) Swamp harrier
Gargano Island eaglesGarganoaetus freudenthali

G. murivorus
Gargano Island Extinct (Late Miocene) Aquila delphinensis
Giant hawkGigantohierax sp. Cuba Extinct Hawks
Harpagornis claw vs eagle.png
Haast's eagle
Harpagornis moorei New Zealand Extinct (c. AD 1400) Little eagle

Booted eagle
Titan-hawk Titanohierax gloveralleni Cuba, Hispaniola and the Bahamas Extinct Hawks


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Anakena Beach parrotsTwo unnamed species Easter Island ExtinctParrots
Broad-billed parrot
Lophopsittacus mauritianus Mauritius Extinct (c. AD 1680) Psittaculine parrots
Strigops habroptilus 1.jpg
Strigops habroptilus New Zealand Critically EndangeredParrots


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Candiacervus ropalophorus.jpg
Cretan owl
Athene cretensis Crete Extinct (Pleistocene) Little owl
Ornimegalonyx oteroi.jpg
Cuban giant owls
Ornimegalonyx spp. Cuba Extinct (Pleistocene) True owls
Tyto gigantea.JPG
Larger Gargano giant owl
Tyto gigantea Gargano Island Extinct (Late Miocene) Barn owls
Tyto pollens.jpg
Andros Island barn owl
Tyto pollens Andros Island, Bahamas Extinct (before AD 1600)
Rivero's barn owl Tyto riveroi Cuba Extinct
Tyto robusta.JPG
Lesser Gargano giant owl
Tyto robusta Gargano Island Extinct (Early Pliocene)


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Leptoptilos robustus.jpeg
Flores flightless stork [19]
Leptostilos robustus Flores Extinct (Late Pleistocene) Greater adjutant

Lesser adjutant


ExampleBinomial nameNative rangeCurrent statusContinental relatives
New Zealand owlet-nightjar Aegotheles novazelandiae New Zealand Extinct (c. AD 1200) Australian owlet-nightjar
New Caledonian owlet-nightjar
Aegotheles savesi New Caledonia Critically endangered


ExampleBinomial nameNative rangeCurrent statusContinental relatives
NovitatesZoologicae18 Pl02 Corvus moriorum.png
Chatham raven
Corvus moriorum Chatham Islands Extinct New Zealand raven
Emberiza alcoveri.jpg
Long-legged bunting
Emberiza alcoveri Tenerife Extinct (after AD 1) Cabanis's bunting

Giant nukupu'u Hemignathus vorpalis Hawaii Extinct (after AD 1000) Finches
Tasmanian superb fairywrenMalurus cyaneus cyaneus Tasmania Least Concern Superb fairywren
Kangaroo Island superb fairywrenMalurus cyaneus ashbyi Kangaroo Island Least Concern
Stout-legged wren Pachyplichas yaldwyni South Island of New Zealand Extinct Passeriforms
Silvereye, Capricorn.JPG
Capricorn silvereye
Zosterops lateralis chlorocephalus Capricorn and Bunker Group of the Australian Great Barrier Reef Unknown Silvereye



ExampleBinomial nameNative rangeCurrent statusContinental relatives
H. thambema Hateg Island Extinct (Late Cretaceous) Quetzalcoatlus


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Brachylophus gibbonsi.JPG
Tongan giant iguana [20]
Brachylophus gibbonsi Tonga Extinct (c. 800 BC) South American iguanids
Lapitiguana impensa.JPG
Fijian giant iguana [21]
Lapitiguana impensa Fiji Extinct (c. 1000 BC)
Sauromalus hispidus - Reptilium Landau.jpg
Angel Island chuckwalla
Sauromalus hispidus Isla Ángel de la Guarda, Baja California Near Threatened Peninsular chuckwalla
San Esteban Island Chuckwalla.jpg
San Esteban chuckwalla
Sauromalus varius San Esteban Island, Baja California Endangered


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Gecko de Delcourt Hoplodactylus delcourti GLAM MHNL 2016 3742.jpg
Delcourt's giant gekko
Hoplodactylus delcourti New Zealand Extinct (c. AD 1870) Diplodactylid geckos
Phelsuma gigas - Giant Rodrigues Gecko - extinct 2.jpg
Rodrigues giant day gecko
Phelsuma gigas Rodrigues Extinct (c. AD 1850) Day geckos
Rhacodactylus leachianus.jpg
New Caledonian giant gecko
Rhacodactylus leachianus New Caledonia Least Concern Diplodactylid geckos


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Vaillant's mabuya Chioninia vaillanti Cape Verde Endangered Mabuyas
Leiolopisma mauritiana - memorial model - Ile aux Aigrettes.jpg
Mauritius giant skink
Leiolopisma mauritiana Mauritius Extinct (after AD 1600) New Zealand Leiolopisma skinks
Macroscincus coctei003.jpg
Cape Verde giant skink
Macroscincus coctei Cape Verde Extinct (after AD 1900) Mabuyas
Terror skink Phoboscincus bocourti Île des Pins off New Caledonia Endangered Skinks

Wall lizards

ExampleBinomial nameNative rangeCurrent statusContinental relatives
La Palma giant lizard Gallotia auaritae La Palma Critically endangered Mediterranean sandrunner lizards
Gallotia bravoana.jpg
La Gomera giant lizard
Gallotia bravoana Gomera Critically endangered
Gallotia goliath mummy 2.JPG
Tenerife giant lizard [22]
Gallotia goliath Tenerife Extinct (c. AD 1500)
Gallotia Simonyi at Centro de recuperacion del lagarto gigante..jpg
El Hierro giant lizard
Gallotia simonyi El Hierro Critically endangered
Gallotia stehlini -Gran Canaria, Canary Islands, Spain-8.jpg
Gran Canaria giant lizard
Gallotia stehlini Gran Canaria Least Concern


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Angel de la Guarda Island speckled rattlesnake Crotalus mitchellii angelensis Isla Ángel de la Guarda off Baja California Least Concern Speckled rattlesnake
Tadanae-jima striped snake population [23] Elaphe quadrivirgataTadanae-jima island off Tokyo Unknown Japanese striped snake
20060306 King Island Tiger Snake.jpg
Island tiger snake populations
Notechis scutatus Mount Chappell Island (Tasmania) and Williams Island, Hopkins Island and the Nuyts Archipelago (South Australia) [24] Least Concern [25] Tiger snake
Isla Cerralvo long-nosed snakeRhinocheilus lecontei etheridgei Jacques Cousteau Island off Baja California Sur Unknown Long-nosed snake

Dubious examples

  • The Komodo dragon and a similar (extinct) giant monitor lizard from Timor have been regarded as 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 , and it has been proposed based on fossil evidence that the ancestors of these varanids first evolved their large size in Australia and then dispersed to Indonesia. [26] If this is true, rather than being insular giants they would be viewed as examples of phyletic gigantism. Nevertheless, given that Australia is sometimes viewed as the world's largest island, the former view may still be valid.
  • Giant tortoises in the Galápagos Islands, the Seychelles, and formerly the Mascarenes and Canary Islands are often considered examples of island gigantism. However, during the Pleistocene, comparably sized or larger tortoises were present in Australia ( Meiolania ), southern Asia ( Megalochelys ), Madagascar ( Dipsochelys ), North [27] ( Hesperotestudo ) and South America [28] ( Chelonoidis , the same genus now found in the Galápagos [29] ), and on a number of other, more accessible islands. [27] In the late Pliocene they were also present in Africa [30] (" Geochelone " laetoliensis [31] ). The present situation of large tortoises being only found on remote islands may reflect that these islands were discovered by humans fairly recently and have not been heavily populated, making their tortoises less subject to overexploitation.


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Birgus latro 2.jpg
Coconut crab
Birgus latro Indian Ocean islands and Polynesia [32] Unknown Coenobita hermit crabs
Giant wetas
Deinacrida spp. New Zealand Variable South African king crickets
Lord Howe Island stick insect Dryococelus australis 10June2011 PalmNursery.jpg
Lord Howe Island stick insect [33] [34]
Dryococelus australis Lord Howe Island Critically endangered Phasmatid stick insects
Giant pseudoscorpion [35] Garypus titanius Boatswain Bird Island off Ascension Island Unknown Garypoid pseudoscorpions
Madagascar hissing cockroaches
Gromphadorhina spp. Madagascar Least Concern Blaberid cockroaches
Labidura herculeana.jpg
Saint Helena earwig
Labidura herculeana Saint Helena Extinct (c. AD 1967) Labidura riparia
Stavenn Megachile pluto.jpg
Wallace's giant bee
Megachile pluto North Moluccas VulnerableContinental bees of subgenus Callomegachile
Sphaeromimus andohahela.jpg
Giant pill-millipedes of Madagascar
Microsphaerotherium spp.

Sphaeromimus spp.

Zoosphaerium spp.
Madagascar UnknownGiant pill-millipedes of India (Arthrosphaera)
Orsonwelles graphicus (Simon, 1900).jpg
Orsonwelles spp. Hawaii Unknown Money spiders
Conants Giant.jpg
Conant's giant Nihoa tree cricket
Thaumatogryllus conanti Nihoa Unknown Tree crickets
Taveuni longhorn beetle.jpg
Giant Fijian long-horned beetle [36]
Xixuthrus heros Viti Levu, Fiji VulnerableAustralasian Xixuthrus species
Taveuni beetle Xixuthrus terribilis Taveuni, Fiji Unknown


ExampleBinomial nameNative rangeCurrent statusContinental relatives
Paryphanta busbyi.jpg
Kauri land snails
Paryphanta spp.

Powelliphanta spp.
New Zealand Near Threatened Other rhytidids


In addition to size increase, island grass plants may also exhibit "insular woodiness". The most notable examples are the megaherbs of New Zealand's subantarctic islands. [37]

ExampleBinomial nameNative rangeCurrent statusContinental relatives
Anisotome latifolia.jpg
Campbell Island carrot
Anisotome latifolia Campbell and Auckland Islands Unknown Apiaceae
Bulbinella rossi and Australasian pipit.jpg
Ross lily
Bulbinella rossii Campbell and Auckland Islands UnknownNew Zealand Maori Lily

South African Yellow Cat-tail
Black-eyed daisy Damnamenia vernicosa Auckland and Campbell Islands Unknown Astereae
Lodoicea Maldivica B.jpg
Coco de mer [38]
Lodoicea maldivica Seychelles EndangeredBorassoid palms
Flora Antarctica Plate XXIV.XXV.jpg Pleurophyllum criniferum Antipodes, Auckland and Campbell Islands Unknown Cineraria
Pleurophyllum hookeri.jpg
Silver-leaf daisy
Pleurophyllum hookeri Macquarie Island, Auckland and Campbell Islands Unknown
Pleurophyllum speciosum (1).jpg
Campbell Island daisy
Pleurophyllum speciosum Campbell and Auckland Islands Unknown
Stilbocarpa polaris.jpg
Macquarie Island cabbage
Stilbocarpa polaris Macquarie Island and New Zealand subantarctic islands Vulnerable Araliaceae

See also


  1. The reduction in predation on islands often also leads to tamer behavior of island prey species, a trend that has been analyzed in lizards. [2] [3]
  2. The earliest known New Zealand kiwi ancestor, a presumed recent arrival from Australia. [16]

Related Research Articles

Carnivore organism that eats mostly or exclusively animal tissue

A carnivore, meaning "meat eater", is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging. Animals that depend solely on animal flesh for their nutrient requirements are called obligate carnivores while those that also consume non-animal food are called facultative carnivores. Omnivores also consume both animal and non-animal food, and, apart from the more general definition, there is no clearly defined ratio of plant to animal material that would distinguish a facultative carnivore from an omnivore. A carnivore at the top of the food chain, not preyed upon by other animals, is termed an apex predator.

Predation A biological interaction where a predator kills and eats a prey organism

Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation and parasitoidism. It is distinct from scavenging on dead prey, though many predators also scavenge; it overlaps with herbivory, as a seed predator is both a predator and a herbivore.

Megafauna large or giant animals

In terrestrial zoology, megafauna are large or giant animals. The most common thresholds used are weight over 40 kilograms (90 lb) or 44 kilograms (100 lb) or over a tonne, 1,000 kilograms (2,205 lb). The first of these include many species not popularly thought of as overly large, such as white-tailed deer and red kangaroo.

Giant tortoise

Giant tortoises are characteristic reptiles that are currently found on two groups of tropical islands: the Aldabra Atoll and Fregate Island in Seychelles and the Galápagos Islands in Ecuador. These tortoises can weigh as much as 417 kg (919 lb) and can grow to be 1.3 m long. Giant tortoises originally made their way to islands from the mainland; for example, the Aldabra Atoll and Mascarenes giant tortoises are related to Madagascar tortoises while the Galapagos giant tortoises are related to Ecuador mainland tortoises. This phenomenon of excessive growth is known as island gigantism or insular gigantism. It occurs when the size of the animals that are isolated on an island increases dramatically in comparison to their mainland relatives. This is due to several factors such as relaxed predation pressure, competitive release, or as an adaptation to increased environmental fluctuations on islands. However, giant tortoises are no longer considered to have been examples of island gigantism, as they originally evolved their massive sizes on the mainland. Giant tortoises were once common across the Cenozoic faunas of Eurasia, Africa and the Americas.

Dactyloidae family of reptiles

Dactyloidae are a family of lizards commonly known as anoles and native to warmer parts of the Americas, ranging from southeastern United States to Paraguay. Instead of treating it as a family, some authorities prefer to treat it as a subfamily, Dactyloinae, of the family Iguanidae. In the past they were included in the family Polychrotidae together with Polychrus, but the latter genus is not closely related to the true anoles.

<i>Megalania</i> species of reptile

Megalania is an extinct giant goanna or monitor lizard. They were part of a megafaunal assemblage that inhabited southern Australia during the Pleistocene. The youngest fossil remains date to around 50,000 years ago. The first aboriginal settlers of Australia might have encountered them and been a factor in their extinction.

Apex predator Predator at the top of a food chain

An apex predator, also known as an alpha predator or top predator, is a predator at the top of a food chain, with no natural predators.

The lava mouse is an extinct endemic rodent from the Canary Islands, Spain. It is the only species in the genus Malpaisomys.

<i>Nephila pilipes</i> species of arachnid

Nephila pilipes is a species of golden orb-web spider. It can be found in Japan, China, Vietnam, Cambodia, Taiwan, Malaysia, Singapore, Myanmar, Indonesia, Thailand, Laos, Philippines, Sri Lanka, India, Nepal, Papua New Guinea, and Australia. It is commonly found in primary and secondary forests and gardens. Females are large and grow to a body size of 30–50 mm, with males growing to 5–6 mm. It is the largest of the orb-weaving spiders apart from the recently discovered Nephila komaci, and one of the biggest spiders in the world.

Island tameness

Island tameness is the tendency of many populations and species of animals living on isolated islands to lose their wariness of potential predators, particularly of large animals. The term is partly synonymous with ecological naïvete, which also has a wider meaning referring to the loss of defensive behaviors and adaptations needed to deal with these "new" predators. Species retain such wariness of predators that exist in their environment, for example a Hawaiian goose retains its wariness of hawks, but lose such behaviors associated with mammals or other predators not found in their historical range. The most famous example is that of the dodo bird, which owed its extinction in a large part to a lack of fear of humans, and many species of penguin - which although wary of sea predators have no real land predator, and therefore are very unafraid and curious towards humans.

Sardinian dhole species of carnivoran

The Sardinian dhole, also known as the Sardinian fox, was an endemic insular canid, that occurred on the Mediterranean islands of Sardinia (Italy) and Corsica (France). Its range was because both Sardinia and Corsica were joined for much of the Pleistocene. It became extinct when humans began to settle on the island. Its scientific name means "dog-beast of Sardinia".

Cozumel raccoon species of mammal

The Cozumel raccoon, also called the pygmy raccoon, is a critically endangered species of island raccoon endemic on Cozumel Island off the coast of the Yucatan Peninsula, Mexico.

Mesopredator release hypothesis

The mesopredator release hypothesis is an ecological theory used to describe the interrelated population dynamics between apex predators and mesopredators within an ecosystem, such that a collapsing population of the former results in dramatically-increased populations of the latter. This hypothesis describes the phenomenon of trophic cascade in specific terrestrial communities.

<i>Ctenosaura hemilopha</i> species of reptile

Ctenosaura hemilopha, also known as the cape spinytail iguana , is a species of spinytail iguana endemic to Baja California. It is arboreal and primarily herbivorous, although it can be an opportunistic carnivore. Males may grow up to 100 centimeters (39 in) in length, while females are smaller, with a length of up to 70 centimeters (28 in). Five subspecies are currently recognized.

Island ecology is the study of island organisms and their interactions with each other and the environment. Islands account for nearly 1/6 of earth’s total land area, yet the ecology of island ecosystems is vastly different from that of mainland communities. Their isolation and high availability of empty niches lead to increased speciation. As a result, island ecosystems comprise 30% of the world’s biodiversity hotspots, 50% of marine tropical diversity, and some of the most unusual and rare species. Many species still remain unknown.

Intraguild predation

Intraguild predation, or IGP, is the killing and sometimes eating of potential competitors. This interaction represents a combination of predation and competition, because both species rely on the same prey resources and also benefit from preying upon one another. Intraguild predation is common in nature and can be asymmetrical, in which one species feeds upon the other, or symmetrical, in which both species prey upon each other. Because the dominant intraguild predator gains the dual benefits of feeding and eliminating a potential competitor, IGP interactions can have considerable effects on the structure of ecological communities.

Diplochory, also known as “secondary dispersal”, “indirect dispersal” or "two-phase dispersal", is a seed dispersal mechanism in which a plant’s seed is moved sequentially by more than one dispersal mechanism or vector. The significance of the multiple dispersal steps on the plant fitness and population dynamics depends on the type of dispersers involved. In many cases, secondary seed dispersal by invertebrates or rodents moves seeds over a relatively short distance and a large proportion of the seeds may be lost to seed predation within this step. Longer dispersal distances and potentially larger ecological consequences follow from sequential endochory by two different animals, i.e. diploendozoochory: a primary disperser that initially consumes the seed, and a secondary, carnivorous animal that kills and eats the primary consumer along with the seeds in the prey’s digestive tract, and then transports the seed further in its own digestive tract.

In evolutionary biology, mimicry in vertebrates is mimicry by a vertebrate of some model, deceiving some other animal, the dupe. Mimicry differs from camouflage as it is meant to be seen, while animals use camouflage to remain hidden. Visual, olfactory, auditory, biochemical, and behavioral modalities of mimicry have been documented in vertebrates.


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