Deer, caribou, bison and other similar animals are often infected by a range of internal parasites, including worms called helminths. Although many of these infections are not lethal, they can still impact health or animal behavior.

For example, infected animals can eat less grass or other vegetation than they normally would. In an interesting twist, this means that a world with more sublethal parasitic infections is a greener world.

A new study, led by Washington University in St. Louis and including a University of Michigan co-author, uses a mathematical model and a global meta-analysis to highlight the cascading consequences of common parasitic infections in wild animals on terrestrial ecosystems.

“Parasites are well known for their negative impacts on the physiology and behavior of individual hosts and host populations, but these effects are rarely considered within the context of the broader ecosystems they inhabit,” said Amanda Koltz, a Washington University biologist and first author of the study published online May 9 in Proceedings of the National Academy of Sciences.

“In this study, we show that pervasive parasitic infections reduce herbivory rates and can therefore trigger trophic cascades that impact plant communities,” Koltz said. “This work helps fill a recognized knowledge gap regarding the ecological consequences of parasitic infections in natural ecosystems.”

U-M biologist Aimée Classen is a co-author of the new study. She provided ecosystem context to the working group and modeling effort, and she collected data as part of the meta-analysis.


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