Food web topology and parasites in the pelagic zone of a subarctic lake


*Correspondence author. E-mail:


  • 1Parasites permeate trophic webs with their often complex life cycles, but few studies have included parasitism in food web analyses. Here we provide a highly resolved food web from the pelagic zone of a subarctic lake and explore how the incorporation of parasites alters the topology of the web.
  • 2Parasites used hosts at all trophic levels and increased both food-chain lengths and the total number of trophic levels. Their inclusion in the network analyses more than doubled the number of links and resulted in an increase in important food-web characteristics such as linkage density and connectance.
  • 3More than half of the parasite taxa were trophically transmitted, exploiting hosts at multiple trophic levels and thus increasing the degree of omnivory in the trophic web.
  • 4For trophically transmitted parasites, the number of parasite–host links exhibited a positive correlation with the linkage density of the host species, whereas no such relationship was seen for nontrophically transmitted parasites. Our findings suggest that the linkage density of free-living species affects their exposure to trophically transmitted parasites, which may be more likely to adopt highly connected species as hosts during the evolution of complex life cycles.
  • 5The study supports a prominent role for parasites in ecological networks and demonstrates that their incorporation may substantially alter considerations of food-web structure and functioning.