Range Expansion of Anolis C. Carolinensis on Chichi-Jima, the Bonin Islands, Japan

Range Expansion of Anolis c. carolinensis on Chichi-Jima, the Bonin Islands, Japan

MASAMI HASEGAWA, TAMOTSU KUSANO AND KAZUYOSHI MIYASHITA

Abstract: Green anole, Anolis c. carolinensis, was introduced onto Chichi-jima, the Bonin Islands, in 1960's, and the incipient colony was successfully established by early 1970's. Green anole expanded its range year after year, and by 1984 the distribution covered about two thirds of the island. Density of green anole was very high at Ohmura where Cryptobrepharus boutonii nigropunctatus was not found. C. b. nigropunctatus was, however, still abundant in areas beyond the penetration fronts of green anole.

Key words: Lacertilia; Anolis c. carolinensis; Bonin Islands; Species introduction

The green anole, Anolis c. carolinensis, native to southeastern North America, has been arti- RESULTS AND DISCUSSION ficially introduced to Chichi-jima, the largest of The time of introduction. -The exact year of the Bonin Islands (Hasegawa, 1986). It is said introduction has not yet been determined. that islanders or American soldiers brought in Shigei (1971) reported on a herpetological several lizards from Guam, the Mariana survey conducted in 1969, but did not refer to Islands, as pets. Several years after the A. c. carolinensis. According to information introduction, they began to increase in the wild obtained from islanders, however, the lizards and gradually expanded their distribution over were already observed in the wild around 1968, the island. In this paper, we describe this although they were very few in number and range expansion and the present status of this restricted to a small area in Ohmura village lizard on Chichi-lima. (personal communication by Mr. K. Hasegawa, a Tokyo-to government officer posted to the METHODS island in 1974). Hara (1986) reported that the The survey of the process of range ex- lizards were commonly observed during the pansion before 1982 is based on the literature area of Ohmura in the years from 1972 to 1974. records and information from islanders and It is considered probable, therefore, that the persons (officially) concerned with the island. actual introduction was made in the period of We conducted field surveys three times during 2 or 3 years before 1968, and that the incipient the period from November 1982 to September colony became successfully established during 1984. Census routes were established on the the period from 1968 to 1972. island as shown in Figure 1. Two or more Range expansion.-Figure 2 shows yearly observers carefully patrolled these routes, and changes in the distribution of Anolis c. caroli- the points where the lizards were newly found nensis since their colonization. Figure 2A is were considered the fronts of penetration into based on the survey conducted by Matsumoto new areas. et al. (1980) in 1979. According to this survey, In order to investigate the present status of the distribution expanded mainly to the north the lizards, ten-minute counts were conducted and east of Ohmura, with a small disjunct area at several selected sites in November 1982, southward at Komagari. This disjunct area of September 1983, and September 1984. The distribution was probably brought about by average numbers of lizards counted were re- artificial (human) transport. corded as relative abundance at respective sites. Figures 2B, C, and D show the results of the In these counts, Cryptoblepharusboutonii nigro- present investigation. The lizards which had punctatus, the only native lizard of Chichi- once primarily expanded toward the north now jima, was also counted, not only at the sites mentioned above, but also at points beyond the penetrated further toward the southern part of range of Anolis c. carolinensis. Chichi-iima each year. Thus by 1984 the distribution covered about two thirds of the island. Penetration toward the south occurred Accepted 2, May 1988 at first along the main traffic roads that run 116 Jpn. J. Herpetol. 12(3). 1988

FIG. 1. Map showing the study sites on Chichi jima, the Bonin Islands. from Ohmura to Mt. Chuosan and Kita- introduced to Haha-iima, the second largest of fukurozawa, then along the branch roads or the Bonin Islands (Mr. M. Nakane, personal derivative (secondary) paths. Expansion oc- communication). curred along such roads because the lizards Density in relation to native lizards.-Table 1 generally prefer sunny places as their habitats shows the relative abundance of A. c. carolinensis (Williams, 1969). Penetration to vacant areas and C. b. nigropunctatus at several selected is still continuing. However, the speed of this points on Chichi-jima. At Ohmura, where penetration has become somewhat slow in A. c. carolinensis occurred at quite a high recent years. This is because more than half of density, C. b. nigropunctatus was not found at the southern part of the island is covered with all, although its abundance just before the dense forests, which are not suitable for A. c. introduction of A. c. carolinensis is unknown. carolinensis. In 1984, the lizards were newly The two species occurred in equal abundance at

TABLE 1. Relative abundances of Anolis c. carolinensis and Cryptobrepharus boutonii nigropunctatus estimated by 10 minutes count at several sites on Chichi-jima, the Bonin Islands. HASEGAWA ET AL. -ANOLIS RANGE EXPANSION 117

FIG. 2. Yearly changes in the distribution of Anolis c. carolinensis on Chichi-jima. Open circles indicate new records of locality, and closed ones previous records cumulated over the years.

Mt. Mikazuki and Kita-fukurozawa. At still abundant. These data suggest that pene- Nagatani and Nakayama pass the density of tration of A. c. carolinensis causes decrease of C. b. nigropunctatus decreased slightly after the C. b. nigropunctatus or that C. b. nigropunctatus penetration of A. c. carolinensis. Beyond the has decreased from unknown environmental penetration fronts of A. c. carolinensis, such as changes and, thereafter, A. c. carolinensis has at Minami-fukurozawa, C. b. nigropunctatus are attained high population densities in such vacant 118 Jpn. J. Herpetol. 12(3). 1988 areas. At present, we do not have enough data HASEGAWA, M. 1986. Ecological studies of the to discriminate these possibilities. Therefore, lizards on Chichi-jima, the Bonin Islands. ecological processes underlying the impact of Ogasawara Kenkyu Nenpo (9): 12-17. (in Japanese). A. c. carolinensis upon C. b. nigropunctatus MATSUMOTO,Y., T. MATSUMOTOAND K. MIYASHITA. will be the subject of future study. 1980. Herpetological survey on Chichi-jima and Haha-jima, the Bonin Islands. Ogasawarashoto ACKNOWLEDGMENTS.-We thank Dr. Ernest E. Sizenkankyo Genkyochousa Houkokusho, Tokyo- Williams for identifying the anoline lizards from to (1): 65-75. (in Japanese) Chichi-jima and for kindly reviewing the manuscript. SHIGEI, M. 1971. Reptiles of the Bonin Islands. We also thank Mr. Kaoru Hasegawa for his valuable J. Fac. Sci. Univ. Tokyo Sect. IV 12 (2): 145-166. information on the status of the species in the late WILLIAMS,E. E. 1969. The ecology of colonization 1960s and Mr. Masatosi Nakane for his information as seen in the zoogeography of anoline lizards on on the species on Haha-jima. People who helped small islands. Quart. Rev. Biol. 44 (4): 345-388. us in the field, Dr. Tadashi Suzuki, Dr. Fumio Hayashi and Mr. Youji Kigasawa, are also ac- Department of Biology, Tokyo Metropolitan knowledged. University, Fukazawa 2-1-1, Setagaya-ku, Tokyo, LITERATURECITED 158 JAPAN (Present Address of MH: Central Museum of Chiba Prefecture, Aoba-cho, Chiba, HARA, K. 1986. Kika Hachuurui (The naturalized 280 JAPAN) reptiles in Japan). Iden (The Heredity) 40 (1): 14-17. (in Japanese)

要旨小笠原諸島,父島におけるグリーンアノールの定着と分布拡大長谷川雅美・草野保・宮下和喜常に高かったが,土着のオガサワラトカゲの生現在,小笠原諸島の父島に生息するグリーン息は確認されなかった。しかし,グリーンアーアノールは1960年代に持ち込まれ,1970年代前ノルがまだ進入していない場所では,オガサワ

半に,島北部の大村を中心に定着したものであラトカゲの密度は比較的高かった。った。その後,年毎に分布域を拡大し,1984年 (158世田谷区深沢2-1-1東京都立大学理学部 9月までには島の約3分の2の地域に分布する生物学教室)(長谷川の現所属:280千葉市青ようになった。大村地区では,本種の密度は非葉町955-2千葉県立中央博物館)