Balance of nature: mange alters an ecosystem (Introduction)

by David Turell , Friday, July 15, 2022, 18:09 (653 days ago) @ David Turell

In Argentina mange on vicunas altered the ecosystem:

https://www.the-scientist.com/notebook/how-mange-remade-an-ecosystem-70146?utm_campaign...

"She had originally set out to study how the predator-prey relationship between pumas and vicuñas (Vicugna vicugna), a llama-like animal, affects nutrient deposition in the park. But she tacked on another research question after she and her colleagues noticed, beginning in 2015, that a sarcoptic mange epidemic was decimating vicuña populations.

"Sarcoptic mange is caused by a mite, Sarcoptes scabiei...Infected animals can lose clumps of fur and develop itchy skin and callouses, sometimes becoming weak and unable to eat enough to sustain themselves. After the mange took hold—likely spread from domestic llamas at a nearby farm, according to a recent study involving some of Monk’s collaborators—researchers in the park soon noticed mangy-looking vicuñas and a pronounced drop in the animals’ numbers...“By our final year of data collection, in 2020, there were just a few family groups that we would see.” Other changes were visible too—for example, grasslands that the vicuñas had previously grazed down to nubby patches were now covered in taller, denser bunches of grass.

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"One of the team’s questions was whether the mange was killing vicuñas directly or merely slowing them down so that they became easier prey for pumas, Monk says. Puma-tracking collars revealed that the number of their kills held steady as the vicuñas’ numbers fell steeply, pointing to the former explanation. (The collars were preprogrammed to fall off in 2017, so the researchers don’t know what happened to kill rates after that.) In parallel, Andean condors that once scanned the landscape of San Guillermo for puma kills to scavenge spent more time away from the park after the vicuña population plummeted.

"Monk and her colleagues realized that the epidemic was an opportunity to study mange’s effects on not just the vicuñas themselves, but the entire ecosystem. For another project, Emiliano Donadío of Fundación Rewilding Argentina and other collaborators of Monk’s had collected data on vegetation coverage at various sites prior to the mange outbreak; they also had tracking information on GPS-tagged pumas (Puma concolor) and Andean condors (Vultur gryphus) that fed in the park. Monk’s role was to gather mange-era data for comparison and analyze any changes that had taken place. To that end, she spent time in San Guillermo driving to the same sites that Donadío’s team had studied and recording factors such as vegetation cover, grass height, and the presence of seed spikes, which indicated that the grasses hadn’t been heavily grazed.

"It also turned out that the increased greenness the researchers had observed wasn’t uniform across the park. “Vegetation exploded in the open plains that are where the vicuñas had foraged most heavily in the past,” Monk explains. Those open plains are relatively safe spaces for the animals, as they make it harder for pumas to approach unseen. But in canyons, which provide more cover for pumas, “we actually saw no change in the vegetation after the outbreak of mange,” she says. “It turns out the vicuñas were already so wary in those habitats that they spent less time foraging there and thus, there wasn’t a change when the population crashed.”

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"Overall, Monk, who expects to graduate next month says, “it was interesting to see how . . . disease can really restructure an ecosystem.” That restructuring, known as a trophic cascade, is more commonly invoked to describe the effects of a predator—most famously, wolves in Yellowstone National Park, which trim elk populations and thus allow the aspen trees that the elk feed on to flourish. Although some previous studies in other systems point to similarly far-reaching effects of pathogens, the “evidence is still pretty thin,” says Julia Buck, a disease ecologist at the University of North Carolina Wilmington who coauthored a 2017 review on the topic but was not involved in Monk’s project. She calls the new paper “a really amazing piece of work” that adds to that evidence. “You wouldn’t think that a tiny little mite would be able to change the whole ecosystem like that,” she says. “But it can.'”

Comment: another study like the one in Yellowstone snowing how delicate an ecosystem is and how easily it can be damaged. It also shows the balanced state affects animal populations and the vegetation they feed upon. And the entire importance of ecosystems is based on food supply. This makes it obvious God's goal of humans had to include an enormous food supply to feed the huge population size humans would create.