Animals help disperse seeds and spores for many plant and fungal species. This typically happens when animals eat the fruiting bodies of plants and fungi and pass seeds and spores through their digestive systems.
Mycorrhizal fungi form symbiotic associations with plant roots, enhancing water and nutrient uptake and playing a central role in forest productivity, regeneration and resilience to environmental stress. Through these connections, mycorrhizal fungi shape forest structure and function by influencing plant establishment, growth and responses to drought and disturbance.
Some fungal species produce above-ground fruiting bodies (mushrooms) that release spores into the air. Many mycorrhizal fungi produce below-ground fruiting bodies, such as truffles, that cannot disperse spores without animal consumers.
Animals facilitate the dispersal of mycorrhizal spores when they consume fungal fruiting bodies and pass spores through their digestive systems. Small mammals are particularly important fungal consumers; however, their limited movement typically restricts spore dispersal to tens or hundreds of meters. This constrained dispersal may limit the ability of mycorrhizal fungi to recolonize disturbed areas and track environmental change across fragmented landscapes.
Carnivores that prey on small mammals may be able to transport fungal spores that were eaten by the prey. When a carnivore eats a small mammal, it can carry the spores in its digestive system and deposit them over long distances, helping fungi move across fragmented landscapes.
This process is called secondary dispersal. However, little is known about how often carnivores disperse mycorrhizal fungi this way or what traits make some carnivores more effective fungal dispersers than others.
New research from the Natural Resources Research Institute (NRRI) at the University of Minnesota, recently published in the journal Ecology Letters, found:
- Mycorrhizal fungal spores were present in 87 percent of small mammals and 67 percent of the carnivore scats examined.
- When spores were present, carnivores dispersed hundreds to more than a billion spores per scat.
- Larger carnivores, such as wolves, tended to disperse spores over greater distances, while smaller carnivores, such as red foxes and fishers, ate more small mammals, dispersed more fungal species, and had higher spore loads in their scats.
- Although all carnivores dispersed mycorrhizal fungal spores, fishers and bobcats were particularly effective due to their high spore loads and long-distance movements.
- Carnivores play an important role in ecosystem function by providing a largely overlooked mechanism for long-distance dispersal of beneficial mycorrhizal fungi.
"Mycorrhizal fungi play such a critical role in ecosystem structure and function," said Michael Joyce, a wildlife ecologist at NRRI and senior author of the study. "When we think about carnivores, we often think about the effects they can have on wildlife communities by killing and eating prey. But these predator-prey relationships can have much broader, positive impacts on ecosystems by providing long-distance dispersal of mycorrhizal fungi. Secondary dispersal of spores is sort of like a relay race, where spores are transferred from the fungi to small mammals and finally to the carnivore who spreads the spores to a new spot."
"Wildlife are doing more than we realized to keep forests healthy," said Alexis Grinde, a wildlife ecologist and Forest and Land Research Group Leader at NRRI who coauthored the study. "Carnivores act as long-distance dispersers of beneficial fungi, helping trees survive stress and disturbance. This hidden partnership may be essential for forest resilience in a changing climate."
According to Joyce, while the study's results suggest that secondary fungal dispersal by carnivores is likely a widespread phenomenon, carnivore species differ in their spore dispersal effectiveness. This work is ongoing, and the research team is continuing to examine additional factors that shape fungal movement across landscapes. In particular, they are currently evaluating how habitat selection by carnivores influences where spores in scats are deposited, which likely also plays a strong role in the dispersal effectiveness.
Funding for the study was provided by the U.S. Forest Service, Northern Research Station; Natural Resources Research Institute at the University of Minnesota; and the Wisconsin Department of Natural Resources.
