Island Gigantism

Island gigantism is a concept in evolution where the size of animals which have been isolated on an island have a proportionately larger body size than their mainland counterparts.

Causes

Island are their own solitary ecosystems that allow for unique evolutionary situations to arise. There are several theories as to why island gigantism.

1. Predator concept- Generally, large mammal carnivores are absent from islands, which allows for bird and reptile species to become top predators in these niches. They are able to grow larger because of this, but generally birds and reptiles are less efficient hunters than mammals. Because of this decrease in predation pressure, herbivores often increase in size too.

2. Island rule- A part of Island Biogeography, the island rule says that members of a species get smaller or bigger depending on the resources or constraints availible in the environment.

3. Founder Effect- Theory that the largest members of a species were those able to establish a population on an island, so therefore the following population is large.

Examples

Some examples of island gigantism are very famous, such as the Galapagos tortoise, which helped form the theory of Natural Selection by Darwin. Some other examples are the extinct Moa, the Dodo, and Komodo Dragon

References

Jaffe, A.L., Slater, G.J., & Alfaro, M.E. (2011). The evolution of island gigantism and body size variation in tortoises and turtles. Biology Letters, 7(4), 558-561.

=====Lomolino, Mark V. I., Sax, D.F., Palombo, M.R., van der Geer, A.A. (2012). Of mice and mammoths: evaluations of causal explanations for body size evolution in insular mammals. Journal of Biogeography, 5, 842-854.
Meiri, S., Raia, P., & Phillimore, A. B. (2011). Slaying dragons: limited evidence for unusual body size evolution on islands. Journal of Biogeography, 38(1), 89-100.=====