It’s well known that when habitat becomes fragmented, wildlife suffers. But now, a study more than two decades in the making has published its findings in Science demonstrating just how rapidly mammals species disappear in fragmented patches of forest.

The study found that mammal species whose habitat becomes fragmented can disappear in as little as 25 years.

When the Chiew Larn reservoir was created in 1987 by damming the Khlong Saeng in Thailand, it flooded the forest valley, creating multiple small islands of fragmented habitat where there had once been a large expanse of continuous forest. A team of researchers led by David Woodruff of the University of California at San Diego recognized the perfect opportunity to study the effects of habitat fragmentation on species. In the early 1990s, they trapped, tagged and released a diversity of animals on 12 of the islands. They did the same in the intact forest surrounding the reservoir. On the smallest islands — those less than 24 acres — they observed extinctions in as little as five years.

Last year, biologist Dr. Luke Gibson of the National University of Singapore returned to the very spot where Woodruff and the team had gathered their data decades earlier. The decline in biodiversity in that short time was stunning. Where Woodruff’s team had tagged between 7 and 12 species of mammal on most of the small islands, Gibson could find only one or two remaining. In contrast, he found no change in the mainland forest.

Complicating matters further, is that one of the mammal species found on the islands — on some islands, the only mammal left — is the Malayan field rat, an invasive species. According to the study, “such biotic invasions are becoming increasingly common in human-modified landscapes.”

Forest habitats are becoming more and more fragmented around the world. Around 90 percent of South America’s Atlantic forest, home to the golden lion tamarin covered in Loose Leaf earlier this week, is destroyed, with the remainder mostly in fragmented patches of less than 200 acres.

And it’s not only tropical forests that are suffering from fragmentation. American Forests Global ReLeaf has worked to create wildlife corridors to connect fragmented habitat for Mexican spotted owls in Angeles National Forest, ocelot in the Lower Rio Grande National Wildlife Refuge and a variety of native species in Exeter, England, among many other projects.