Island gigantism

Island gigantism is the evolutionary tendency for some island animals to grow larger than related mainland forms. It is especially common among small-bodied species isolated from predators or competitors.

Island rule: The tendency for small animals on islands to evolve larger bodies and large animals to evolve smaller bodies. Island gigantism is the large-bodied side of this proposed size pattern.
Dodo: An extinct, flightless pigeon native to Mauritius in the Indian Ocean. Its large body and loss of flight are often discussed as outcomes of island evolution.
Island biogeography: The study of how island area, isolation, colonization, and extinction shape species diversity. Its principles explain how isolation creates distinctive evolutionary settings for body-size change.
Island ecology: The study of ecological processes and interactions in island environments. Gigantic animals can reshape feeding relationships in small, isolated ecosystems.
Ecological release: An increase in a species’ access to resources or habitats after constraints such as competitors or predators are reduced. Reduced competition can let island populations exploit larger prey or new food sources.
Komodo dragon: A large monitor lizard native to several Indonesian islands. Its exceptional size makes it a living example of insular body-size evolution.
Insular biogeography: The study of the distribution and evolution of organisms in isolated habitats, especially islands. It situates gigantism within the broader history of isolated island lineages.
Trophic cascade: An ecological chain reaction in which changes at one trophic level affect other levels. Large island predators can alter prey populations and indirectly change vegetation.
Predator release: An increase in survival or ecological opportunity when predators are absent or scarce. Fewer predators can favor larger body size when size improves defense or competitive ability.
Giant tortoise: A group of very large tortoise species native to islands in the Galápagos and Indian Ocean. Island populations independently evolved immense size in distinct oceanic settings.

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