Isolation in an island environment often results in the development of organisms larger than their mainland counterparts. Examples of this phenomenon include the tortoises of the Galapagos islands, and the Va ranus komodensis lizards in the Komodo, Rindja, and Flores Islands of Indonesia (Cloudsley-Thompson, 1977). Case et al., 1992, suggest that insular gigantism is associated with more territorial taxa with low population densities, whereas insula r dwarfism occurs among less territorial taxa with high population densities. In addition, they state that prey size and prey abundance directly influence the magnitude of body size change.
Food availability on an island would increase due to a loss of competition for the same food source, and a warmer maritime climate. Abundance of food increases growth rates and ensures long survivorship for organisms. A lack of predators also promotes longevity. Both phenomena lead to growth-related larger achieved body size.
Sexual behaviour may also have something to do with it. Large territorial males tend to mate often with many females, and thus pass on their larger body size genes. This eventually results in a phenotypic increase in body size of the entire island population.