ńͪӚǮ?ҟͅсӇτҫ?ƦˊȱŰ͇Ƚ©ѽ 1ŀϺ ώ 2*

Diversity in land snail communities on Minami-Iwo-To Island
Shinichiro WADA1 & Satoshi CHIBA2*
1. ӐҀƩǂʪÊ ̀ǹǂͨΆͷӞ192-0397 ʪÊҀĉ̺ƻǼńƩˮӟ
Tokyo Metropolitan University, School of Science & Engineering, Minami-Osawa Hachioji, Tokyo
192-0397
2. ʪĹƩǂ ʪĹ[p[ͨΆs¥v¨Ӟ980-8576 ǌƒ͞ÑŚǼҶϺĽǶĎ 41ӟ
Tohoku University, Center for Northeast Asian Studies, Tohoku UniversityӢ41 Kawauchi, Miyagi, 980-8576* schiba@cneas.tohoku.ac.jp (author for correspondence)Йʆ 2017 ȅ 6 ʙ<ńͪӚǮ?ҟͅсӇ?жʴXЉ;41жʴ<Q47ȣRU1ɾ)ͣЛ<ƕ67
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Figure 1ӤA map of Minami-lwo lsland with a climbing route. Closed circles indicate survey sites.
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Table 1. Species list of land snails found on Minami-lwo IslandӤHabitat use, distribution type and biogeographicalgroups to which each species belongs are shown.
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Figure 3. A relationship between altitude andspecies richness and species diversity index(Simpson index).

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Ɔ 4. 5 5?̱̈́ƌ̀h¡¨?ˋӕ&9?Ӄȍėǽ
Figure 4. Relationships between altitude and frequencies of individuals belonging to five biogeographic groups ofspecies.ӨӣӨӤ̈́˹ș d]Ӈ8@ˋӕ 320m ƌ̥8,U?ͿNˎ­ȱRƌ­ȱ<o~)1̥Xҝ#Aƙ
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− 323 −

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Figure 6. Polymorphisms in genital morphology in Vertigo kodamai. EuphallicӞAӟand aphallicӞBӟ.
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SUMMARY

Diversity in land snail communities on Minami-Iwo-To Island
Shinichiro WADA1 & Satoshi CHIBA2*
1. Tokyo Metropolitan University, School of Science & Engineering, Minami-Osawa Hachioji, Tokyo, 192ӣ0397
2. Tohoku University, Center for Northeast Asian Studies, Tohoku UniversityӢ41 Kawauchi, Miyagi, 980ӣ8576* schiba@cneas.tohoku.ac.jp (author for correspondence)
A survey of land Mollusca on Minami-Iwo-To Island was conducted in June 2017. Information on land snail
fauna was revised and 14 species were recorded. Among these species, Lamellidea sp. seems to be a new species
endemic to the island. A graph of species diversity in relation to the altitude of the survey sites exhibited a humpshaped curve, supporting the hypothesis of mid-domain effects, with individual species distributed within a limited
range of altitudes and showing niche conservatism. Species derived from northern Eurasia dominated at high altitude
sites, while those from the tropical Pacific were observed at low altitude sites. Although many of the observed species
showed niche conservatism in terms of habitat use, Vertigo kodamai showed expanded habitat use on the island, andV. dedecola showed habitat shifts at low altitudes. These patterns may reflect the initial stages of adaptive divergenceof these species. Polymorphisms in genital morphology, including aphallism and euphallism, were found in V.
kodamai populations, suggesting that reproductive traits potentially contribute to the success of long distancedispersal and extension of habitat use. Characteristics of snail populations (e.g., density) observed in the present
survey were largely different from those seen in previous surveys, implying temporal changes in the structure andcomposition of the island snail community on the island.
Key words
Adaptation, Environmental gradient, Evolution, Kazan Islands, Ogasawara Islands.

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