Ecological Diversification of Insular Terrestrial Reptiles: A Review of the Studies on the Lizard and Snakes of the Izu Islands

抄録

　Terrestrial vertebrates of the Izu Islands are the subset of species indigenous or endemic to the Japanese main islands, but their species composition is extremely disharmonic both taxonomically and ecologically. Mammals, amphibians and freshwater fishes are impoverished due to isolation, the small area, reduced habitat diversity and lack of permanent freshwater habitats, whereas birds and reptiles are rather rich in endemic species or subspecies with unique ecological characteristics, and those groups of vertebrates maintain higher population densities particularly on the islands without mammalian carnivores. The snake Elaphe quadrivirgata, a top predator on most of the islands, shows remarkable diversification in food habits and body size in accordance with inter-island difference in intensity of interspecific competition with other snake species and in availability of prey. The lizard Eumeces okadae, a small insectivorous predator in intermediate trophic level, shows variation in life history traits in relation to different predation pressures. The lizard populations exhibiting delayed maturity and lower reproductive rates due to less than annual reproduction exist only on the islands without snakes or mammalian carnivores. Introduction of the weasel for controlling rat pests in agricultural products almost extirpated lizard populations with little adaptation to novel predators, and subsequently caused significant changes in entire island food web structures.