Aim: Plants on islands are often subjected to lower levels of herbivory relative to those at mainland sites. As a consequence, island plants are predicted to exhibit lower levels of physical and chemical defences, which renders them more susceptible to introduced herbivores. Yet, instances of high pressure by superabundant herbivores native to islands have been reported in many insular systems, which presumably would result in heightened plant defences. To date, no quantitative review has been...