Human-induced disease outbreak in animals causes cascading ecological effects

The study published in Ecology Letters is unique in that it tracked the cascading effects of the deaths of the vicuñas, which are wild South American camelids, from the disease on vegetation and biodiversity in the region.

"We largely don't have many examples in literature of how a rapid-disease outbreak can cause effects, not just on populations, but throughout the ecosystem. So, this provides really important context,'' says YSE PhD student Julia Monk, a lead author of the study.

Monk, a student in the lab of YSE Oastler Professor of Population and Community Ecology Oswald Schmitz, who also co-authored the report, was doing field work in the high desert of San Guillermo National Park in the Andes when mange ravaged the vicuñas. She was studying the important role that pumas and their prey play in carbon storage and nutrient cycling on landscapes.

The impact of the loss of vicuñas from disease were significantly different than the deaths of vicuñas by predation from pumas, Monk and a team of researchers discovered.

"What is really different about what we found was that we were able to track the change in ecosystem function, from a system governed by pumas as the top predator to a system dominated by this disease and to determine that they're not analogous. You don't just swap out one for the other. We actually had completely diverging outcomes based on which was a dominant source of mortality for these vicuñas,'' says Justine Smith, assistant professor of ?wildlife, fish, and conservation biology at University of California, Davis, who was co-lead author of the study. The deaths from mange led to an increase in vegetation as well as a reduced presence of condors, that forage off vicuñas carcasses killed by pumas in the national park.

"Disease transmission between wildlife and domestic animals can be catastrophic for both players, threatening local livelihoods and disrupting natural processes in protected areas. As land use modification and fragmentation continue to increase interactions between domestic and wild animals, disease-dominated trophic cascades may come to supplant predators as top-down forces in some systems,'' the study notes.

Recent research indicates the outbreak of mange was linked to domestic llamas that were released outside the park.

Smith says the study points to the importance of tracking the effects of disease outbreaks globally.

"It's hard for us to anticipate all of the ways that people can change ecosystems. There are a lot of interacting effects, and I think we're going to continue to see rapidly restructured ecosystems,'' says Smith. "And that is something that we need to learn a lot more about if we're going to create conservation plans in the changing world that we live in."

The study highlights the need to prepare for more impacts of human-induced wildlife disease outbreaks and how it affects conservation.

"Developing strategies for human-wildlife coexistence and protected areas management that minimize the exchange and spread of disease will be critical for the conservation of ecosystems sustained by tightly connected food webs as well as the preservation of human health and livelihoods,'' the study states.

Schmitz says when nature threw Monk and Smith a curveball in the field when the disease broke out, they quickly were able to recognize important analysis.

"They co-led an environmental data science analysis comprehensively showing how an explosive disease outbreak, could quickly unravel a long-running ecosystem state, in a putative protected area no less. It is a sober reminder of how human transformation of the planet outside of protected areas can have unintended but far-reaching, consequences,'' Schmitz says.