So-called rain forest islands are proving to be no refuge for certain species of small mammals, a recent study has uncovered. 

Published in the journal Science, the study found that rain forest fragmentation is wiping out species of small animals faster than once believed. It also revealed that the species living in these fragmented environments are at increased danger from invasive species as well.  Luke Gibson -- co-author of the study and a biologist at the National University of Singapore -- told BBC's "Science in Action" that the team didn't expect "such a dramatic change from 20 years ago." He likened the extinction of the species to "an ecological Armageddon."

"Our study focused on small mammals, but what we did not report was a similar near-complete extinction of medium to large-sized mammals, such as elephants, tigers and tapirs, which are now completely absent from these islands in the reservoir," said Gibson. "All of these animals were all in the forest landscape before the creation of the reservoir."

The study was completed at the Chiew Larn reservoir in southern Thailand. The national park was flooded during the mid-1980s to create a reservoir, reports the BBC. The increased water levels created more than 100 islands of tropical forest that the team used for the study. The reservoirs' islands were identified as a good location to analyze the rate of species decline on forest fragments by David Woodruff of the University of California at San Diego, reports the New York Times. Between 1992 and 1994, numerous species of small mammals on 12 of the islands and the surrounding reservoir were trapped, tagged and released by Woodruff's team. This process was completed each day for a week, with the team tagging any animals they found.

Gibson followed up that initial study in 2012, returning to the same islands to trap any mammals he could find. Shockingly, after a week of setting checking traps, none of the seven species documented during Woodruff's first survey were found. But Gibson's traps did catch a culprit he feels has contributed to depleting the species' numbers along with fragmentation -- the Malayan field rat.

"Native mammals suffered the harmful effects of population isolation, and they also had to deal with a devastating invader - the Malayan field rat," he said of the invasive species of rats that quickly grew to numbers large enough to displace several native mammal species on the islands. 

Identified as one of the major issues threatening biodiversity worldwide, habitat fragmentation is usually the effect of man-made alterations to natural environments. Natural disasters can also lead to fragmentation, though. A co-author of the study, William Laurance, stresses that the key to protecting biodiversity from the growing threat of fragmentation is to ensure that "large, intact habitats" continue to be protected to ensure native species continue to thrive in these habitats.