To clarify the modification of physical defences of Glochidion obovatum Sieb. et Zucc., we compared the length of spine-like branches and frequency of lateral branches of G. obovatum between Kashima Island, which supports a high density of sika deer (Cervus nippon), and its neighbouring areas. The length of spine-like branches of G. obovatum in Kashima Island was not significantly longer than that of the neighbouring areas, but the frequency of lateral branches on the island was higher than that of the neighbouring areas. Since the branches of G. obovatum are heavily foraged by the sika deer, the shrub form of the species has evolved into the bonsai form, suggesting increased frequency of occurrence of lateral branches, which could develop as shoot-like branches. Thus, the observed features are facultative defence mechanisms of G. obovatum against heavy browsing in a small-sized island with very high density of sika deer.
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