1. 11-1-803, Mizuhodai, Izumiku, Sendai 981-3125, Japan;
2. Okinawa Prefectural Agricultural Experiment Station, 4-222, Sakiyama-cho, Naha, Okinawa 903-0814, Japan;
3. Laboratory of Animal Population Ecology, Faculty of Agriculture, Okayama University, 1-1-1 Tsushima-naka, Okayama 700-8530, Japan;