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Tiny parasite disrupts an entire ecosystem in the high Andes

A new study published in the journal Ecology Letters has examined the cascading effects of a mange outbreak on the high Andes ecosystem of Argentina’s San Guillermo National Park. Before the 2015 mange outbreak, vicuñas, pumas, and condors have been intrinsically connected, with vicuñas grazing the grass, pumas preying on them, and condors feeding on the pumas’ leftovers. However, after mange nearly wiped out the entire vicuña population, these relationships quickly unraveled, profoundly destabilizing the ecosystem.

Sarcoptic mange is caused by parasitic mites that burrow under the skin of animals, triggering excruciating pain that stops the animals from moving or foraging. The outbreak in San Guillermo probably stemmed from domestic llamas that were introduced to private lands outside the park in 2015. 

“This preserve is about as remote as you can get, with very little human interaction, and yet it is still not safe from human activities occurring hundreds of miles away,” said study co-lead author Justine Smith, as assistant professor at the University of California, Davis. “Pathogens can take hold quickly, leaving animals with little time to respond or adapt. We might see unintended consequences that we should be preparing for when managing at-risk populations of wildlife.”

Before this outbreak, pumas had been the biggest threat to vicuñas. However, this tiny mite proved to be much more dangerous than the large predators, decimating the park’s vicuña populations in a few years. When their main food source disappeared, condors eventually left the park altogether, while pumas needed to switch to other food sources, such as small rodents, in order to avoid starvation.

These changes among the animals also caused massive landscape changes. Bare ground became covered in grass over huge expanses visible from space, and vegetation increased by 900 percent in areas where vicuñas used to graze.

“We don’t really know how or if these systems will recover,” said Smith. “Will they return to the system we knew, or will a new balance emerge from these dynamics? It’s hard to predict.”

“Continuing to support our colleagues in Argentina who have worked for decades to understand and protect this unique system will be vital for tracing the continuing effects of the disease and for promoting the ecosystem’s recovery,” concluded study co-author Julia Monk.

By Andrei Ionescu, Staff Writer

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