Protected but not safe: Hidden threats to wildlife in tropical forests

Tropical forests are among the most vibrant ecosystems on Earth. These dense and humid landscapes hold more than 60% of all known species, making them irreplaceable biodiversity storehouses.

Despite covering less than one-tenth of the planet’s surface, they sustain an extraordinary number of plants, animals, and microorganisms.

However, this natural wealth faces unprecedented threats. Expanding agriculture, infrastructure, and industrial activities are rapidly transforming vast sections of tropical land. The loss of these forests is not just about trees; it is about the countless species that depend on them for survival.

Among these are some of the world’s most endangered creatures, now pushed closer to extinction due to human encroachment.

Limits of protected areas

Conservation efforts have sought to curb this destruction through the establishment of protected areas. Governments and international organizations continue to create new reserves, hoping to slow the decline of species at risk.

However, recent research published in PLOS Biology suggests that setting aside protected land may not be enough.

Professor Lydia Beaudrot of Michigan State University contributed significantly to this study. As an ecologist in the Department of Integrative Biology, she leads research focused on the conservation of tropical mammals.

Beaudrot and her colleagues brought together an international team of scientists to assess the effects of human activity on mammal populations.

“We found that tropical forests near more people have fewer mammal species. It suggests that some species do not survive even when forests are protected, such as in national parks,” Beaudrot explained.

Human presence and tropical forests

It is widely understood that deforestation and land conversion pose serious risks to wildlife. However, this study highlights another, more subtle danger – human presence itself.

Even when forests remain intact, the simple fact that people live nearby can disturb the delicate balance of life within these ecosystems.

The researchers described this effect as “anthropogenic extinction filtering.” This process shows that human activity outside protected areas reshapes the ecological communities within them. Hunting, noise pollution, and habitat disturbance all contribute to changes that make it difficult for certain species to survive.

To measure this phenomenon, the research team deployed over 2,000 camera traps across South America, Africa, and Asia. These devices captured an unparalleled dataset, offering insights into the biodiversity of tropical forests on a global scale.

Global network for conservation science

The images collected came from a collaborative effort involving 17 research sites established under the Tropical Ecology Assessment and Monitoring Network. This organization brings together conservationists and scientists to study biodiversity in the most remote tropical regions.

Ilaria Greco, a doctoral candidate at the University of Florence and the study’s lead author, took this collaboration a step further.

She worked with an even broader network of international researchers, securing data not available through existing wildlife monitoring programs. This expansion resulted in the most comprehensive study of its kind, covering 37 tropical forest locations.

By analyzing long-term data on 239 mammal species, the researchers could compare how biodiversity changed in response to varying levels of human presence. The study examined forests ranging from vast, uninterrupted landscapes to fragmented patches surrounded by human settlements.

Additional conservation measures

While protected areas remain essential, Beaudrot stressed that they cannot function as isolated islands. Additional conservation efforts, such as forest restoration, are necessary to provide a buffer between human activities and vulnerable wildlife populations.

To better understand the connection between human density and mammal survival, the researchers developed a model integrating remote-sensing data with information from trail cameras. This approach allowed them to visualize the extent of human influence on wildlife populations.

“Through a massive collaboration among many researchers, we used the largest dataset to date to test how habitat loss and human density affect tropical forest wildlife,” Beaudrot said.

Impact on mammals in tropical forests

The model predicted a direct correlation between human population density and biodiversity loss. It estimated that for every 16 humans living within a square kilometer of a protected area, mammal species could decrease by as much as one percent.

This finding highlights a major challenge: even where forests remain formally protected, external human activities influence the survival of species within them.

The lack of adequate buffer zones makes many of these conservation areas vulnerable to long-term biodiversity decline.

Danger of fragmented tropical forests

One of the most striking aspects of this research is its revelation about the edges of tropical forests. Nearly 70% of tropical forest habitats lie within one kilometer of a forest’s edge. This means that very few of these ecosystems remain untouched by human influence.

Mammal populations were also negatively affected by habitat loss occurring as far as 50 kilometers (31 miles) away from their core forested regions. Such extensive impact suggests that conservationists need to think beyond the immediate borders of protected areas.

“It is not just the protected area that matters for biodiversity conservation but also what is outside the protected area,” Beaudrot emphasized.

A new depth of understanding

“Until recently, we have not had high-quality data at a global scale to measure how people affect the number of mammal species and how widely they occur within tropical forests,” noted Beaudrot.

The study provides the most detailed picture yet of how human activity shapes biodiversity in tropical forests. The findings show that simply setting land aside for conservation is not enough.

Without addressing external pressures, these areas may fail to protect the species they were designed to safeguard.

Rethinking conservation strategies

Efforts like the United Nations’ Decade on Ecosystem Restoration and the Kunming-Montreal Global Biodiversity Framework aim to halt biodiversity loss. However, the study warns that these initiatives may not fully account for the complex ways human activities threaten tropical wildlife.

To create more effective conservation strategies, the researchers argue that efforts must extend beyond protected area borders. Reducing human impact outside conservation zones is crucial to maintaining biodiversity.

Restoring degraded land surrounding protected forests can help expand buffer zones, offering species a greater chance to survive. Rather than relying on isolated patches of land, conservationists may need to focus on connecting and expanding protected areas to create larger, continuous habitats.

A call to strengthen protection

Greco, who led the project, now works as a postdoctoral researcher at the University of Florence under Francesco Rovero.

According to Greco, the study’s results suggest that “anthropogenic extinction filtering” is actively shaping mammal communities in tropical forests.

She explained that human overpopulation has already driven the most sensitive species to local extinction. The species that remain in these landscapes now depend largely on habitat cover.

“The study warns that conservation of many mammals in tropical forests depends on mitigating the complex detrimental effects of anthropogenic pressures well beyond protected area borders,” said Rovero.

Moving forward with conservation

This research sheds light on the urgent need for a more comprehensive approach to biodiversity conservation. While protected areas remain a critical tool, they must be supported by broader land management strategies.

Strengthening connections between conservation zones, restoring degraded land, and reducing human impact on surrounding landscapes will be key to protecting the world’s remaining tropical forests.

The study is published in the journal PLOS Biology.

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