Comparative Morphology of Prickles of Rubus croceacanthus (Rosaceae) in Kashima Island and Its Neighbouring Areas

摘要

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. Lev. (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.