Kashima Island (32º57′N, 132º27′E) is a very small island (45.1 ha) in southwestern Shikoku, Japan with a high density (ca. 38.5/km 2 ) of Sika deer (Cervus nippon). To examine induced defences of plants against the Sika deer, we conducted morphological analyses of prickles of Rubus sieboldii Blume (Rosaceae) between grazed (Kashima Island) and ungrazed areas (neighbour locations) in southwestern Shikoku. The length and density of prickles on leaves and around stems were measured. The prickles of the plants on Kashima Island were significantly longer and denser than those of the other areas, implying that the increased length and density of prickles were an induced defence of R. sieboldii on Kashima Island.

We compared the leaf morphology and anatomy of the putative rheophytic ecotype of Viola mandshurica W. Becker var. ikedaeana (W. Becker ex Taken.) F. Maek. and its closely related variety, V. mandshurica var. mandshurica. We showed that the leaf of the rheophytic ecotype of V. mandshurica var. ikedaeana was narrower than that of V. mandshurica var. mandshurica. Moreover, the leaf thickness and guard cell size of the rheophytic ecotype of V. mandshurica var. ikedaeana were significantly larger than those of V. mandshurica var. mandshurica. We further showed that leaves of the rheophytic ecotype of V. mandshurica var. ikedaeana contained fewer cells than did those of V. mandshurica var. mandshurica. Our results suggest that the narrower leaves of V. mandshurica var. ikedaeana are caused by a decrease in the number of cells. A narrower leaf may enable the rheophytic ecotype of V. mandshurica var. ikedaeana to resist the strong flow of water that occurs after heavy rainfall, while a thicker leaf may enhance tolerance to desiccation and highintensity light.

To determine the effects of sika deer (Cervus nippon) browsing on the physical defences of the Japanese pricklyash "Zanthoxylum ailanthoides Sieb. et Zucc." (Rutaceae), we compared the length and density of prickles on Japanese islands which were under different browsing pressures. We measured the length and density of prickles on the midribs, leaf rachis, and stems. We found that the prickles of Z. ailanthoides on Kashima island were not significantly longer or at higher densities than those in the neighbouring areas; the longest pickles at the highest densities were found on Akune island. The density of sika deer on Akune (ca. 520 -600/km 2 ) was higher than that on Kashima (ca. 38.5/km 2 ), and consequently, Akune was under greater browsing pressure. Our results suggest that the increased length and density of prickles on Akune is a response by Z. ailanthoides to the high density of sika deer found on the island.

Kashima Island (32° 57′ N, 132° 27′ E) is a small island of southern Japan with high population density of sika deer (Cervus nippon). To ascertain whether heavy sika deer browsing has resulted in increased plant defences on the island, we conducted a morphological comparison of Rubus croceacanthus H. Lév. (Rosaceae) on Kashima Island and in the neighbouring areas on the mainland. We measured the length and density of the leaf and stem prickles. We found that the prickles of R. croceacanthus on Kashima Island were significantly longer and at a higher density than those in the neighbouring areas, suggesting that increased prickle length and density is an adaptive defence against sika deer browsing.

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.