Sublethal effects of parasitism on ruminants can have cascading consequences for ecosystems

Amanda M. Koltz, David J. Civitello, Daniel J. Becker, Sharon L. Deem, Aimée T. Classen, Brandon Barton, Maris Brenn-White, Zoë E. Johnson, Susan Kutz, Matthew Malishev, Daniel L. Preston, J. Trevor Vannatta, Rachel M. Penczykowski, Vanessa O. Ezenwa

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


Parasitic infections are common, but how they shape ecosystem-level processes is understudied. Using a mathematical model and meta-analysis, we explored the potential for helminth parasites to trigger trophic cascades through lethal and sublethal effects imposed on herbivorous ruminant hosts after infection. First, using the model, we linked negative effects of parasitic infection on host survival, fecundity, and feeding rate to host and producer biomass. Our model, parameterized with data from a well-documented producer–caribou–helminth system, reveals that even moderate impacts of parasites on host survival, fecundity, or feeding rate can have cascading effects on ruminant host and producer biomass. Second, using meta-analysis, we investigated the links between helminth infections and traits of free-living ruminant hosts in nature. We found that helminth infections tend to exert negative but sublethal effects on ruminant hosts. Specifically, infection significantly reduces host feeding rates, body mass, and body condition but has weak and highly variable effects on survival and fecundity. Together, these findings suggest that while helminth parasites can trigger trophic cascades through multiple mechanisms, overlooked sublethal effects on nonreproductive traits likely dominate their impacts on ecosystems. In particular, by reducing ruminant herbivory, pervasive helminth infections may contribute to a greener world.

Original languageEnglish
Article numbere2117381119
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number20
StatePublished - May 17 2022


  • feeding rate
  • helminth
  • herbivore
  • producer
  • trophic cascade


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