The Length and Density of Prickles on Zanthoxylum ailanthoides (Rutaceae): A Comparison of Japanese Islands with Different Sika Deer Browsing Pressures

摘要

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/km2) was higher than that on Kashima (ca. 38.5/km2), 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.