INSECT PARASITOID SPECIES RESPOND TO FOREST STRUCTURE AT DIFFERENT SPATIAL SCALES

There is now a solid body of theoretical work(1-4) demonstrating that the spatial structure of the habitat combined with animal movement str ongly influence host-parasitoid dynamics. The spatial pattern over whi ch parasitoid search takes place can be affected by the distribution o f the hosts(5), by the spatial arrangement of the host's habitat(6) an d by the spatial scale at which the parasitoid perceives variation in host abundance(7,8). Empirical work, however, has been largely restric ted to small-scale field studies of less than one hectare(6,9) with ve ry few larger(10,11). Here we report initial results of a many-year, l arge-scale study that is among the first to examine the interaction be tween a population-level process (parasitism) and anthropogenic forest fragmentation at large and at multiple spatial scales. We demonstrate that parasitism by four species of parasitoids attacking the forest t ent caterpillar, Malacosoma disstria, is significantly reduced or enha nced depending on the proportion of forested to unforested land. Each of the parasitoid species responds to this mosaic at four different sp atial scales that correspond to their relative body sizes, Our data gi ve empirical support to the argument that changes in landscape structu re can alter the normal functioning of ecological processes such as pa rasitism, with large-scale population consequences(3'4).