Researchers have made a surprise discovery of giant lizards thriving in the Malaysian Sabah region of Borneo island at oil palm plantations, which are more often associated with threatening animal species and deforestation.

The team of scientists that was investigating how scavenging animals were adapting to the monoculture palm oil plantations found unexpected results when they compiled their data from the animals they trapped, an 18 October article in The Conversation by PhD candidate Joshua P Twining said.

“Scavengers are an important but often overlooked group in understanding how ecosystems function,” Twining, who was part of the research group, wrote. “They provide vital services including the removal of carrions, which is a crucial component in recycling nutrients and preventing disease, and disruption of these groups has possible far-reaching implications.”

In the jungles and border regions, the team found animals such as civets, otters, mongooses and pigs, but the closer they got to the plantations where the land had been disturbed and human activity was frequent, the fewer species they found until only one stood out – the Southeast Asian water monitor.

The lizards – having survived largely unchanged for 17M years – were considered pests and scavengers by locals, but were actually active and opportunistic hunters, with a “phenomenal ability” to eat practically anything that fits in their stomachs, from invertebrates and amphibians to birds, small mammals and even their own young.

The monitors’ tendency to regurgitate their stomach contents under stress allowed the scientists to browse through their recent meals, which shed light on how they had come to survive in the plantations, said Twining.

“We found truly mind boggling items, from human refuse such as instant noodle wrappers through to porcupine spines that are so hard and sharp they pierce through human skin with ease and deter almost all other predators,” he wrote.

Not being picky eaters allowed the lizards to proliferate in the plantations as they faced less competition from mammalian scavengers and predators due to higher temperatures and lower plant density.

The plentiful supply of food from natural and human sources, combined with fewer threats, allowed the water monitors to reach what Twining described as “terrifying sizes and high numbers”.

But he added that the oil palm plantations might in the longer term prove an ecological trap, where the apparent reptilian paradise could become the undoing of the very lizards it helped thrive.

The easy availability of food was attracting primarily males, Twining noted, and the growing numbers of large and aggressive monitors could result in territorial battles leading to serious injuries and such heavy energy expenditure that the additional food would not be enough to make up for it.

Additionally, having so many lizards in close proximity provided not only ample opportunities for parasites to spread, but given the low number of females and the water monitors’ penchant for cannibalism, it was unlikely that their few offspring could reach adulthood.

“For now, these giant lizards appear healthy, but in the long run, due to the culmination of adverse effects, water monitors may be doomed to the same fate as the mammals that once inhabited the space,” said Twining.