Dominant parasitoid species diminishes food web structural complexity and function.

Biodiversity and food web ecology are interconnected in the study of community dynamics, being related to underlying factors, such as complexity, productivity, and community assembly. Biodiversity can contribute to increasing the ecosystem function, but its effect on consumer trophic levels remains inconclusive. We generated a multitrophic seed-herbivore-parasitoid food web based on seed traits, insect species abundance and richness, structural and functional food web attributes and the relationship between the seed biomass and the number of eggs laid by the herbivorous beetle Stator maculatophygus. We hypothesized that the food web structure (i.e., connectivity, linkage density and connectance) was determined by the parasitoid trophic levels. Our second hypothesis was that food web functionality (e.g., the parasitism rate) was not affected by the dominance of a single parasitoid species. From the seeds of a plant species (Senegalia tenufolia) (primary trophic level), we recorded nine species and four trophic levels, with one herbivore and seven parasitoids. A significant positive relationship was found between the number of eggs laid and the seed biomass. Connectivity and linkage density were affected by the parasitoid trophic level, and the dominance of a single parasitoid species led to decreases in the structural complexity and the parasitism rate. We described the relationship between structure and function in the field in a multitrophic host-parasitoid food web. The biodiversity of parasitoids plays an important role in the food web, maintaining its complexity and functionality. Synergies between processes acting at lower and higher levels may be driving the food web patterns presented here. Implications for insect conservation: Our results highlight the positive role of parasitoid insect biodiversity in the biological population control of herbivorous insects in this microhabitat (fruit/seed). This demonstrates the importance of public policies aimed at the conservation of natural areas to maintain the diversity and ecosystem functions performed by parasitoid insects. [ABSTRACT FROM AUTHOR]