Phytophagous insects and web-building spiders in relation to pasture vegetation complexity

We investigate the potential use of structural characteristics of vegetatio n as predictors of the densities of pasture arthropods in three Azorean isl ands. Two types of upland pastures, recent sown pastures (3-4 yr old) and w et semi-natural old pastures (> 35 yr old), were studied in three Azorean i slands (S. Maria, Terceira and Pico). Three arthropod assemblages. of parti cular importance in pasture habitats, were assessed: insect forb-feeders, i nsect grass-feeders and web-building spiders. These are numerically abundan t and represent a range of feeding strategies. Point quadrats for plants an d suction (Vortis) for arthropods were used as sampling methods. Several ve getation indices were investigated, but only three (cover abundance of pere nnial forbs, cover abundance of perennial grasses and the total vegetation alpha-diversity) were good predictors of invertebrate abundance. Vegetation structure, defined by a Height Index, was of minor predictive value. In so wn and semi-natural pastureland. diverse and structurally complex pasture s ites support more individual insect forb-feeders. grass-feeders and web-bui lding spiders per unit area than less complex ones.