Current Status of the Introduced Common House Gecko, Hemidactylus frenatus (Squamata: Gekkonidae), on Amamioshima Island of the Ryukyu Archipelago, Japan

Abstract

I surveyed distribution and abundance of a recently established population of Hemidactylus frenatus on Amamioshima Island of the Ryukyu Archipelago, Japan. I also attempted to evaluate the risk of further range expansion of this species within the island. In the first record of H. frenatus from the island in 2000, its range was restricted to one building in the urban area of Naze. In my survey in 2012, however, the gecko was already widespread, being the most abundant gekkonid species in the area. Hemidactylus frenatus was also found in many sites of the island outside Naze, most of which were located in the eastern part of the island. Based on the species distribution model, this eastern biased range expansion seems to reflect the greater abundance of suitable habitats in the eastern part. Two of the three western sites of H. frenatus were isolated from its major, contiguous range in the central-eastern parts by areas with apparently unsuitable habitats and scattered favorable habitats occupied by other gekkonid species, suggesting that H. frenatus there had originated from individuals artificially transported within the island. The species distribution model also indicated the presence of suitable but unoccupied habitats in the southwestern part, predicting further range expansion of H. frenatus on Amamioshima in the future. My survey demonstrated the scarcity of geckos other than H. frenatus in the eastern part, probably as a result of the predominance of H. frenatus there. Based on my field observations, I also discuss the possible major carrier of H. frenatus on Amamioshima.