A hierarchical multi-scale analysis of the spatial relationship between parasitism and host density in urban habitats

Abstract

Studies on spatial density dependence in parasitism have paid scarce attention to how changes in host density at different hierarchical scales could influence parasitism in an herbivore at a particular scale. Here, we evaluated if rates of parasitism per leaf (by the whole parasitic complex and by dominant species) of the specialist leaf miner Liriomyza commelinae (Diptera: Agromyzidae) respond to variations in host density at the leaf, plant patch and site levels in an urban setting. We used multi-level Bayesian models that incorporate the spatial hierarchy occurring in this system, as well as habitat factors previously found to have an effect on the L. commelinae parasitoid community in an urban context (patch size, patch isolation and urbanization level). According to the fitted model, overall parasitism rates decreased with increasing number of mines per leaf, being independent of host-density variations at patch and site level. Patch structure was found to have a strong effect on parasitism rates per leaf. The analysis of parasitism by parasitoid species separately showed consistent results with the response at community level. These results suggest that parasitism of the parasitoid community here studied would be sensitive to hierarchical cues related to the host at the leaf level and to the host habitat at the patch level.