Interactive effects of nutrient enrichment and the manipulation of intermediate hosts by parasites on infection prevalence and food web structure

Parasites with complex life cycles frequently increase their transmission to definitive hosts (where reproduction occurs) by increasing the susceptibility of intermediate hosts to predation by definitive hosts. While recent evidence finds that anthropogenic driven habitat alterations can alter host–parasite relationships, whether such alterations interact with intermediate host manipulation to influence infection prevalence and food web structure remains unknown. We develop a nutrient-limited food web model to investigate how manipulation of intermediate host susceptibility, nutrient supply, and predator diversity determine parasite abundance and infection prevalence in intermediate and definitive hosts. We show that the effects of intermediate host manipulation on parasite abundance and infection prevalence depend on nutrient supply while the coexistence of competing definitive hosts and “dead-ends” (where parasites cannot reproduce) depends primarily on intermediate host susceptibility to predation. Our results suggest that anthropogenic changes in nutrient supply will interact with host–parasite relationships to determine parasite abundance, infection prevalence, and food web structure.