The restoration of parasites, parasitoids, and pathogens to heathland communities

Higher trophic level species such as parasites, parasitoids, and pathogens are frequently ignored in community studies, despite playing key roles in the structure, function, and stability of ecological communities. Furthermore, such species are typically among the last in a community to reestablish due to their reliance upon lower trophic level resources and a requirement for persistent, stable ecological conditions. Consequently their presence alone can be indicative of healthy ecosystems. Using replicated, quantitative food webs we studied the impacts of a restoration treatment upon the interactions of a tri-trophic community consisting of plants, their bumble bee pollinators, and the parasites, parasitoids, and pathogens of the bumble bees at heathland sites. We found the lower trophic levels of the community successfully reinstated at restored relative to control sites. However the abundance, load per host, prevalence of parasitism, prevalence of superparasitism, and host range of a key dipteran parasitoid of the family Conopidae were all significantly reduced in restored heathlands. Potential causes for this incomplete reestablishment at restored sites include the lag in floral resources due to differences in floral species composition, and the reduced ability of this parasitoid species in accessing host resources relative to other natural enemy species present in these communities. Moreover the incomplete reinstatement of the natural enemy community was found to significantly reduce levels of network vulnerability (a measure of how vulnerable prey is to being consumed) at restored sites relative to ancient, control networks.