Deforestation Is Stressing Mammals Out

Deforestation in the Atlantic Forest of South America has destroyed over 90% of the land and is causing rodents and marsupials to experience heightened levels of stress as a result of severe habitat loss. 

A mouse opossum (Gracilinanus agilis) from a deforested area of the Atlantic Forest, eastern Paraguay. (Credit: © Noé U. de la Sancha, Field Museum)

(CN) — Amid the climate crisis ravaging the world, a study released Thursday shows that mammals in the threatened Atlantic Forest in South America experience stress about the danger of deforestation looming over their homes.

The Atlantic Forest is one of the most ecologically diverse places in the world, second only to the Amazon rainforest. It is home to hundreds of species of mammals, reptiles and amphibians, birds and thousands of plant species that are all under attack. 

The forest has been chipped away over the years to make way for urbanization and agriculture. Conservationists have worked tirelessly to protect what is left of the forest, but today less than 10% still stands and is severely fragmented, with many patches under environmental protections. 

In the study, published in the journal Scientific Reports, a team of researchers checked up on the inhabitants of this rich yet vulnerable ecosystem.

“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,” said co-author Noé de la Sancha, a research associate at the Field Museum in Chicago and associate professor of biology at Chicago State University, in a statement. 

“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,” de la Sancha added.

The tropical forest once spanned over an astonishing 463,000 square miles, covering parts of Brazil, Argentina, Uruguay, and Paraguay. To put that number into perspective, that much land is larger than California, Oregon, Washington, and Nevada combined. Since deforestation began there, the forest has lost an immense amount of habitability due to development of farmland, largely for coffee and sugar but also for cattle and eucalyptus.

As a result of this deforestation, the inhabitants of the forest face more threats than ever, since habitat loss is among one of the biggest reasons why species go extinct. Displacement inevitably leads to an increase in competition for resources with animals in surrounding areas, exposure to predators and hunters and dips in population sizes. 

Furthermore, many forest species are endemic, meaning that they only exist in their specific habitat, which is why approximately 60% of Brazil’s endangered species live in the Atlantic Forest.

The authors of the study hypothesized that the remaining animals living in this disrupted forest were likely stressed, or rather more stressed than those in less impacted forests. While some stress is normal for wild animals, and it can help protect them from imminent danger, chronic stress can be damaging.

“A stress response is normally trying to bring your body back into balance,” said co-author David Kabelik, an associate professor of biology and chair of the neuroscience program at Rhodes College. “If something perturbs you and it can cause you to be injured or die, the stress response mobilizes energy to deal with that situation and bring things back into a normal state. It allows you to survive.”

He added: “But then these animals are placed into these small fragments of habitat where they’re experiencing elevated stress over prolonged periods, and that can lead to disease and dysregulation of various physiological mechanisms in the body.”

The team traveled to eastern Paraguay to conduct their research, as it has lost a tremendous amount of forest land to agriculture and lumber. They sectioned off areas spanning from 4.9 to 2,965 acres and collected hormone samples from the fur of five rodent species and two marsupials. 

They explained that gathering samples from their fur instead of their blood would allow them to get a better idea of how much stress hormones each mammal had been expressing over time, rather than just at the time of collection.

“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,” Kabelik said, “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.”

After analyzing their samples, the researchers found higher levels of the stress hormone glucocorticoid in animals from smaller patches of remaining forest than those from larger areas. 

Lead author Sarah Boyle, associate professor of biology and chair of the environmental studies and sciences program at Rhodes College, noted how these findings were not surprising after considering how much change their homes had undergone.

“In particular, these findings are highly relevant for countries like Paraguay that currently show an accelerated rate of change in natural landscapes. In Paraguay, we are just beginning to document how the diversity of species that are being lost is distributed,” said co-author Pastor Pérez, a biologist at Universidad Nacional de Asunción. “However, this paper shows that we also have a lot to learn about how these species interact in these environments.” 

Learning how forest dwelling animals cope with deforestation and habitat loss can allow conservationists to plan accordingly. Boyle added how important this research is, as little is known about species in tropical rainforests, and the team hopes that their work can reach far past its original purpose.

“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,” said de la Sancha. “By destroying natural habitats, we’re potentially creating hotspots for zoonotic disease outbreaks.”

“Big picture, this is really important because it could be applicable to forest remnants throughout the world,” de la Sancha said. “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.”

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