Abstract
Parasites comprise a significant proportion of species on Earth yet are seldom included or realistically represented in studies of food web ecology. As ecosystems continue to change in response to natural and anthropogenic pressures, it is important now more than ever to include parasites to improve our understanding of their role, now and in the future. A large-scale biodiversity survey of the coastal marine ecosystem of Otago, New Zealand, provided a unique opportunity to assess what contribution parasitological studies can make toward revealing trophic interactions between species when creating food webs. Here, we created 4 increasingly complex food web depictions of Otago and compared network properties between them to assess changes with each addition of new types of data (first excluding and then including parasite species). We also assessed how parasites influence the functioning of Otago's food web by simulating extinction scenarios for each web, estimating their robustness to biodiversity loss. The inclusion of parasites altered food web structure, such as decreasing connectance and increasing path length, modularity and species clustering. In both extinction scenarios, including parasites resulted in a lower robustness of the food webs to biodiversity loss. Our results suggest that neglecting parasite taxa in food web studies may lead to inappropriate estimates of ecosystem structure and functioning and possibly an overestimation of an ecosystem's resilience to change. Above all, we reveal the huge potential of parasitological studies to advance our understanding of predator-prey interactions.