Analysis of causative factors in the geographic variation of Sika deer (Cervus nippon) in Japan.

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Only one species of deer, Sika deer (Cervus nippon), inhabit various environments from subarctic coniferous forests (Hokkaido) to subtropical bamboo bush (Kerama Islands) in Japan. As the result of the measurements of over 10,000 specimens, the figures of body size, body weight, skull and antler size show the tendency to clinal decrease from Hokkaido towards the Kerama Islands. The skull length, straight antler length and body weight of Hokkaido stags were 32cm, 62cm, and 120kg respectively, and those of the Kerama Islands stags were 23cm, 30cm, and 30kg respectively.The deer of Hokkaido are slightly larger than those of the largest northern subspecies on the Asian continent, C. nippon hortulorum. The size of the deer from the Kanto and Kinki districts appears to be similiar to that of the five subspecies of Chinese continental Sika deer. The deer from the southernmost range of Kyushu are smaller than the same species in western China. The smaller size of the southern Sika deer in Japan indicates the neotenic changes of their growth.Differences in size not only on climatic differences, due to ecological conditions. On the Kinkazan and Goto Islands, the deer show a low quality (low performance) population under high density, and the deer of Tsushima Island and Tanegashima Island reveal a high quality population which has developed from low density. The neotenic changes of the Yaku deer is thought to be due to the specialized behaviour, namely their adaptation to high and steep mountainous environments. The variation of Sika deer in Japan is attributed to the absence of interspecific segregation and the wide climatic variation.