Imagine an entire ecosystem turning upside down because of a lethal virus – that's the shocking reality that unfolded on Pulau Ubin in 2023, sparking a remarkable surge in one of the world's tiniest hoofed creatures. But here's where it gets controversial: is this population explosion a conservation triumph, or could it hint at unforeseen ecological imbalances that might unravel in the coming years?
SINGAPORE – Back in 2023, a devastating virus known as African swine fever, which wreaks havoc on pigs worldwide by causing severe illness and high death rates, decimated nearly every wild boar on Pulau Ubin. This event didn't just alter the island's wildlife; it set the stage for a dramatic shift that mammal expert Marcus Chua, from the Lee Kong Chian Natural History Museum at the National University of Singapore (NUS), was eager to capture on camera and in data. He hypothesized that the sudden disappearance of these wild pigs (scientifically called Sus scrofa) would create a golden opportunity for the greater mouse-deer (Tragulus napu), a diminutive species often celebrated as the smallest hooved mammal globally.
These pint-sized mouse-deer, weighing no more than about 4kg each, have long been a staple in Malay folklore, where they're portrayed as clever heroes brimming with bravery and sharp intelligence (you can read more about their cultural significance in this Straits Times article). Once believed to have vanished from Singapore's landscape, Dr. Chua played a key role in their rediscovery on the island in 2008, marking the end of an 80-year gap in local sightings. His studies revealed that mouse-deer likely vied with wild boars for essential resources like space, fallen fruits, and low-growing plants – a competition that kept their numbers in check.
'While we haven't documented wild pigs directly preying on mouse-deer, these pigs are notorious for hunting other deer and their young,' Dr. Chua explained. 'With competition and potential predation in the mix, it was crucial to investigate the broader repercussions of this viral outbreak on the island's delicate balance.'
The outcomes were nothing short of astonishing. Just one year after the swine fever hit, mouse-deer populations skyrocketed, reaching an incredible 293 individuals per square kilometer between 2019 and 2024 – a fivefold increase that made spotting these elusive animals unavoidable during surveys. 'It became impossible to go on a survey without encountering a mouse-deer,' Dr. Chua remarked.
This density stands as the highest ever recorded for mouse-deer anywhere on the planet, at least three times greater than what's seen in other locations. It effectively transforms Pulau Ubin into the ultimate hotspot for observing these shy forest dwellers, who typically inhabit woodlands across South-east Asia. For comparison, Cambodia's Southern Cardamom National Park has recorded around 80.7 lesser mouse-deer (Tragulus kanchil, a close relative that's even smaller) per square kilometer. And this is the part most people miss: these findings, published in the scientific journal Biological Conservation on October 25, underscore how mouse-deer can reproduce quickly, with females becoming capable of breeding just five months after birth.
The sharp drop in wild boar numbers likely fueled this boom by easing competition for food and allowing the forest floor vegetation to bounce back and flourish. Dr. Chua believes this marks the first clear evidence in Asia of African swine fever's ecological ripple effects. Thanks to over 15 years of collaborative surveys with the National Parks Board (NParks), his team could pinpoint exactly how the disease reshaped the forest's inner workings.
'It serves as a wake-up call for other regions battling African swine fever to assess both immediate and lasting effects on forest ecosystems,' he added. 'For those managing forests, it highlights the importance of a holistic approach – tackling a disease in one species can trigger profound changes for many others.'
Yet, this peak in mouse-deer numbers might not endure. Signs of wild boars rebounding through breeding emerged just a year after the outbreak, and it's uncertain if the mouse-deer population has hit its environmental limits, known as carrying capacity. 'As wild pig numbers recover, the habitat's carrying capacity for mouse-deer will probably adjust until the interactions between these species settle into a new equilibrium,' Dr. Chua noted. An NUS master's student is now tracking both populations two years post-outbreak to monitor these evolving dynamics.
Wildlife ecologist Matthew Luskin from the University of Queensland, who has studied African swine fever's impacts in South-east Asia, described the research as part of 'a long tradition in ecology of showing how tweaking one species can unleash unexpected chain reactions.' Distinguished Research Professor William Laurance from James Cook University echoed this, suggesting similar patterns could play out in other forests. 'Forests like Malaysia's Pasoh Forest Reserve have experienced wild swings in pig populations from swine fever, leading to notable ecological shifts,' said the conservation expert, who examines global environmental challenges. For instance, in 2022, a Pasoh boar population crash allowed young trees to flourish, as the pigs' destructive nesting habits were no longer a threat.
On Pulau Ubin, however, both Dr. Luskin and Dr. Laurance agree that the mouse-deer surge probably won't cause major disruptions to the forest, since these gentle herbivores are far less impactful than the burlier wild boars.
The study also offers practical insights into wildlife monitoring. Researchers discovered that for abundant species like the mouse-deer, walking straight-line paths at night (a method called line transect sampling) provides more accurate population estimates. This technique counts every spotted animal along a set distance to calculate hidden numbers mathematically. Meanwhile, camera traps prove invaluable for rarer, more secretive creatures, such as the recovering wild boars.
Beyond these natural factors, Dr. Chua attributes the mouse-deer's comeback partly to NParks' dedicated reforestation initiatives and their choice to let vegetation grow undisturbed over decades. His co-author, Robert Teo, NParks' director for Pulau Ubin, hailed the increase as 'a positive step forward for wildlife protection on the island, where we've planted over 40,000 trees so far.' The board plans to keep up these efforts to create richer habitats for local animals.
Interestingly, past attempts by the Singapore Zoo and NParks to reintroduce greater mouse-deer into central Singapore failed, with no mainland sightings until 2012, when Dr. Chua spotted them in the Western Catchment forests. On the other hand, the lesser mouse-deer (Tragulus kanchil), another native species, has managed to hang on in places like Bukit Timah and the Central Catchment Nature Reserve all these years. (For a related story, check out this article on a lesser mouse-deer rescue.)
But here's where it gets even more thought-provoking: is this surge in mouse-deer a model for conservation success, or does it raise concerns about over-reliance on diseases to 'fix' ecosystems? Could human interventions like reforestation be just as powerful – or perhaps more ethical – than letting nature's cruel twists dictate wildlife fate? What do you think: should we embrace these viral-driven changes as opportunities, or actively manage them to prevent potential downsides? Share your views in the comments – I'd love to hear differing perspectives on this ecological rollercoaster!
