Abstract
The green anole Anolis carolinensis invaded the Ogasawara Islands in Japan, drove various native species to extinction, and its distribution expanded 14 years after initial establishment. A. carolinensis invaded Okinawa Island, but it has not expanded its distribution in more than 25 years, although its density is extremely high in the southern region. To determine whether A. carolinensis has the potential to expand its distribution on Okinawa Island, we performed phylogenetic analysis of mitochondrial ND2 DNA sequences to study the origin of A. carolinensis that invaded Okinawa Island. We further used a species distribution model (MaxEnt) based on the distribution of native populations in North America to identify ecologically suitable areas on Okinawa Island. Nucleotide sequence analysis shows that the invader A. carolinensis originated in the western part of the Gulf Coast and inland areas of the United States and that a portion of the anoles on Okinawa was not introduced via the Ogasawara Islands. The MaxEnt predictions indicate that most areas in Okinawa Island are suitable for A. carolinensis. Therefore, A. carolinensis may have the potential to expand its distribution in Okinawa Island. The predictions indicate that habitat suitability is high in areas of high annual mean temperature and urbanized areas. The values of precipitation in summer in the northern region of Okinawa Island were higher compared with those of North America, which reduced the habitat suitability in Okinawa Island. Adaptation to low temperatures, an increase in the mean temperature through global warming, and an increase in open environments through land development will likely expand the distribution of A. carolinensis in Okinawa Island. Therefore, we must continue to monitor the introduced populations and be alert to the possibility that city planning that increases open environments may cause their range to expand.
Highlights
A. carolinensis may have the potential to expand its distribution throughout Okinawa Island
A. carolinensis was introduced to Okinawa Island more than 25 years ago, yet its distribution remains restricted to its southern region
We used a combination genetic and distribution-modeling techniques to determine whether introduced A. carolinensis has the potential to expand its distribution on Okinawa Island
Summary
The Naha Nature Conservation Office of the Ministry of the Environment Japan (2010, 2011) reported that viable populations of A. carolinensis are established in five populations in three areas in Naha City and Tomigusuku City (Figure 1c). When suitable areas on Okinawa Island were predicted according to those for North American populations, high suitability values encompassed the entirety of Okinawa Island, the present distribution of introduced populations was limited to the southern region (Figure 5a). Mean diurnal range (bio2) and precipitation of warmest quarter (bio18) were outside the training range in North America, which might decrease the accuracy of the prediction for Okinawa Island When we excluded these parameters for the prediction, highly suitable areas in North America and the effects of environmental variables were similar, but the suitability in Okinawa Island was higher compared with those in the prediction for all parameters (Figure 5b). The values of precipitation of warmest quarter (bio18) in the northern region of Okinawa Island were higher compared with those of North America, and habitat suitability decreased with increasing the value of bio (Figure 4)
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