Responses of brambles, Rubus vestitus, to herbivory.

We investigated the effect of fertilisation and multiple episodes of simulated herbivory on the prickliness of bramble, Rubus vestitus. The prickliness of fertilised, uncut plants was significantly greater than that of plants in all other treatments. Our results indicate that prickle production is constrained by resource availability, with brambles allocating resources to growth under intense herbivory. Isozyme electrophoresis of plants collected from Wytham Woods, Oxford, UK, failed to detect any variation, suggesting that observed variation in prickliness may be primarily the result of phenotypic plasticity. In our experiments, however, we observed significant variation in prickliness among putative genotypes.