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As countries work toward the 30x30 target under the Kunming-Montreal Global Biodiversity Framework, protecting 30 per cent of land and sea by 2030, a new study highlighted a major gap in conservation efforts.
Merely increasing the size of protected areas is insufficient to protect biodiversity. A study published on February 13, 2025 in PLOS Biology revealed that even in protected areas, tropical mammals remain at risk due to human activities outside these zones.
The research, led by Ilaria Greco of the University of Florence, Italy, and colleagues, described a process called "extinction filtering", where species sensitive to human disturbance disappear, leaving only those that can survive in degraded landscapes. This means conservation efforts must go beyond protected areas to truly safeguard biodiversity.
"Our results suggest the existence of anthropogenic extinction filtering acting on mammals in tropical forests, whereby human overpopulation has driven the most sensitive species to local extinction while remaining ones are able to persist, or even thrive, in highly populated landscapes and mainly depend on habitat cover," said lead author Ilaria Greco in a press release.
Tropical forests have the highest diversity of mammal species on Earth, many of which are already endangered. Governments worldwide are expanding protected areas to meet biodiversity targets under the Kunming-Montreal Global Biodiversity Framework. However, this study showed that simply increasing protected areas is not enough.
Researchers analysed 239 mammal species across 37 tropical forests on three continents to understand how human activities affect wildlife. They found that when forests outside protected areas are cut down or fragmented, the number of mammals inside protected zones drops. Likewise, in areas where human populations are dense, fewer mammal species remain.
"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 co-author Francesco Rovero, of the University of Florence, Italy in the press release.
Scientists collected nearly 560,000 camera-trap images from tropical forests in Asia, Africa, and the Americas. They measured the number and distribution of species in each area and tested how these patterns responded to human activities like deforestation and population growth.
Satellite data helped researchers track changes in land use and forest loss. Their analysis found that for every 16 people per square kilometre living near a protected area, mammal diversity declined by 1 per cent. This means that even when wildlife is inside a protected zone and humans are outside, human activities still impact biodiversity.
The study identified two major threats to tropical mammal species. These are forest loss and fragmentation and high human population density.
When forests are broken into smaller patches, species struggle to survive. Some populations shrink, while others disappear completely.
Further, in areas with more people, sensitive species are often the first to vanish, leaving behind only those that can tolerate human disturbances.
This pattern of biodiversity loss, called "extinction filtering", results in a less diverse and more uniform mix of species in tropical forests. Over time, this weakens entire ecosystems and reduces their ability to recover from environmental changes.
Conservation efforts must also address threats in the wider landscape, such as deforestation and human expansion.
Effective strategies should include:
Creating wildlife corridors to connect isolated forest patches so species can move freely
Sustainable land-use planning to limit habitat destruction outside protected areas
Community-based conservation programs that involve local people in protecting biodiversity
Strengthening buffer zones around protected areas to shield species from human activities
The problem of "extinction filtering" is not unique to tropical forests. Across the world, human activities are affecting wildlife inside protected areas. This research provides critical insights for global conservation efforts, especially as countries work to meet biodiversity targets under the Kunming-Montreal Global Biodiversity Framework.
As countries increase the number of protected areas, they must also address the bigger challenge: How to protect species from threats beyond these borders.