CSU, Associate Professor of Biology, Discovers the Effects of Deforestation on Mammals in South America’s Atlantic Forest

Scientific Report will feature Faculty’s findings

Mammals in South America’s Atlantic ForestChicago, Illinois – Chicago State University’s (CSU) Noé de la Sancha, Associate Professor of Biology and Field Museum research associate, found that deforestation is placing stress on rodents and marsupials that can result in greater disease outbreak among wildlife and humans. The study will be published in Scientific Report, along with findings from co-authors and research lead Sarah Boyle, an Associate Professor of Biology and Chair of the Environmental Studies and Sciences Program at Rhodes College, and Pastor Pérez, a biologist at Universidad Nacional de Asunción. By analyzing hormones that accumulate in fur, researchers found that rodents and marsupials living in smaller patches of South America’s Atlantic Forest are under more stress than ones living in more intact forests. 

“We suspected that organisms in deforested areas would show higher levels of stress than animals in more pristine forests, and we found evidence that that’s true,” says Noé de la Sancha, a research associate at the Field Museum in Chicago, Associate Professor of Biology at Chicago State University, and co-author of a new paper in Scientific Reports detailing the discovery. “Small mammals, primarily rodents and little marsupials tend to be more stressed out, or show more evidence that they have higher levels of stress hormones, in smaller forest patches than in larger forest patches.”

Scientific Research

For this study, the researchers focused on patches of forest in eastern Paraguay, a particularly hard-hit area in the last century, as the region was clear-cut for firewood, cattle farming, and soy. To study the effects of this deforestation, the researchers trapped 106 mammals from areas ranging from 2 to 1,200 hectares—the size of a city block to 4.63 square miles. The critters they analyzed included five species of rodents and two species of marsupials.

The researchers took samples of the animals’ fur since hormones accumulate in the hair over periods of many days or weeks and could present a clearer picture of the animals’ typical stress levels than the hormones present in a blood sample. “Hormones change in the blood minute by minute, so that’s not really an accurate reflection of whether these animals are under long-term stress or whether they just happened to run away from a predator a minute ago,” says Kabelik, “and we were trying to get at something that’s more of an indicator of longer term stress. Since glucocorticoid stress hormones get deposited into the fur over time, if you analyze these samples you can look at a longer term measure of their stress.”

The team found that the animals from smaller patches of the forest had higher glucocorticoid stress hormones than animals from larger forest patches. “Our findings that animals in the small forest patches had higher glucocorticoid levels was not surprising, given the extent to which some of these forested areas have been heavily impacted by forest loss and fragmentation,” says Boyle.

Further Study 

The study has also led to further findings, such as how these small animals pass diseases to humans. “If you have lots of stressed out mammals, they can harbor viruses and other diseases, and there are more and more people living near these deforested patches that could potentially be in contact with these animals,” says de la Sancha. “By destroying natural habitats, we’re potentially creating hotspots for zoonotic disease outbreaks.” 

The researchers say the results of this study go far beyond South America’s Atlantic Forest. “Big picture, this is really important because it could be applicable to forest remnants throughout the world,” says de la Sancha. “The tropics hold the highest diversity of organisms on the planet. Therefore, this has potential to impact the largest variety of living organisms on the planet, as more and more deforestation is happening. We’re gonna see individuals and populations that tend to show higher levels of stress.”

Its neighbor, the Amazon, often overshadows the Atlantic Forest. Still, the Atlantic is South America’s second-largest forest, extending from northeastern Brazil down south along the Brazilian coastline, into northwestern Argentina to eastern Paraguay. It once covered about 463,000 square miles, an area bigger than California, Oregon, Washington, and Nevada combined. Since the arrival of Portuguese colonists 500 years ago, parts of the forest were destroyed to make space for farmland and urban areas; today, less than one-third of the original forest remains.