Geographical patterns of butterfly species diversity in the subtropical Ryukyu Islands: the importance of a unidirectional filter between two source islands
1. Institute of Low Temperature Science, Hokkaido University, Kita, Sapporo, Japan;2. Faculty of Science, University of the Ryukyus, Nishihara, Okinawa, Japan;3. Faculty of Science, Chiba University, Chiba, Japan