Why Are There No Predators on Lombok Island?

When someone crosses the Bali Strait toward Lombok — a mere thirty kilometers — they are not just traveling between islands. They are, in fact, crossing one of the sharpest biogeographic boundaries on Earth: the Wallace Line. This line is not merely an imaginary mark on a map but a biological frontier separating two worlds — the Asian fauna to the west and the Australasian fauna to the east.

The impact of this invisible boundary is strikingly clear on Lombok Island — no large predators live there.

This phenomenon was first recorded by British naturalist Alfred Russel Wallace, who explored the Indonesian archipelago in the 19th century. In his classic book The Malay Archipelago (1869), Wallace described the astonishing contrast between the wildlife of two neighboring islands.

In Bali, he found monkeys, deer, and Asian-like birds. But as soon as he crossed the narrow strait to Lombok, those animals vanished, replaced by brightly colored parrots, cockatoos, and marsupials like the cuscus — all characteristic of Australasian fauna.

Modern research later confirmed Wallace’s observations. The Lombok Strait, which reaches depths of about 300 meters, acts as a formidable barrier preventing large land animals from crossing. Even during ice ages, when sea levels dropped by more than 100 meters, the islands of Bali and Lombok remained separated by deep waters.

Evidence from Modern Science

One of the most comprehensive studies of Lombok’s fauna was conducted by the Western Australian Museum, titled The Wild Mammals of Lombok Island: Nusa Tenggara, Indonesia – Systematics and Natural History. The researchers recorded only around 24 native terrestrial mammal species, most of them bats, rodents, and small civets. There were no records of large predators like tigers, leopards, or bears.

Scientists describe Lombok’s mammal community as “depauperate mammalian fauna,” meaning a notable absence of large mammals compared to islands west of the Wallace Line, such as Java and Bali. Since Lombok was never connected to the Sunda Shelf, large Asian mammals never reached its shores.

A similar conclusion was drawn by evolutionary biologist Ernst Mayr, whose work in The Quarterly Review of Biology strengthened Wallace’s theory. Mayr observed that the distribution of large mammals ends abruptly at Bali — not a single genus of big land animals from mainland Asia ever crossed into Lombok. “Although the distance between islands is small,” he wrote, “the depth of the sea between them forms an absolute barrier for terrestrial mammals.”

Geologically, the Lombok Strait is part of the Wallacea Trench, a deep-sea region dividing two continental shelves: the Sunda Shelf (Sumatra, Java, Borneo) in the west and the Sahul Shelf (Papua, Australia) in the east. For millions of years, these seas have remained deep and never exposed land bridges, even during extreme glacial periods.

Paleoceanographic studies show that much of the Lombok Strait exceeds 250 meters in depth, more than enough to prevent land mammals — which generally cannot swim long distances — from ever crossing.

No Predators in Lombok Island

The absence of large predators has profound ecological consequences. In Lombok’s forests and mountains, there are no tigers, no sun bears, not even large wild boars like those of Java. The role of “top predator” is instead occupied by birds of prey — eagles and owls — and by large reptiles such as pythons and monitor lizards.

According to the Western Australian Museum’s ecological assessments, Lombok’s food chain is significantly shorter than that of larger islands. With no apex predators, small animals like rats, squirrels, and ground-dwelling birds face little predation pressure. Their populations can grow quickly, creating unique ecosystem dynamics.

For local communities, this absence of big predators offers a practical benefit — life in the hills and rural areas is relatively safe from wild animal attacks. Farmers need not fear tigers stalking their livestock, as once happened in Java.

Yet this imbalance also brings challenges. Without natural predators, rodent populations can rise rapidly, damaging crops. To counter this, local people rely on owls and snakes as natural pest control — an example of humans adapting to fill an empty ecological role.

Lombok and the Legacy of Wallacea

The lack of big predators does not make Lombok biologically poor. On the contrary, the island’s isolation has created endemic species found nowhere else on Earth. Some of its birds, lizards, and small mammals have evolved independently for millions of years.

Lombok lies within Wallacea, a transitional zone that bridges — and divides — Asia and Australia. Here, the range of Asian species ends, and the realm of Australasian life begins. The Wallace Line that cuts through the Lombok Strait stands as a living symbol of this ancient separation.

Modern biogeographers now view Lombok as a natural laboratory for studying how isolation shapes evolution and ecology. Without large predators, every species faces different selective pressures, resulting in a fascinating mix of Asian and Australasian traits.

But this delicate balance is fragile. Human activities — land conversion, hunting, and the introduction of foreign species like feral cats and dogs — threaten to disrupt an equilibrium that has existed for millennia.

That is why scientists from the Western Australian Museum and Indonesian conservation groups emphasize the need to protect Lombok’s biodiversity — not only for its beauty but because it preserves living evidence of evolutionary processes separated by deep seas for millions of years.

If Java’s wild tigers once symbolized the power of nature, then in Lombok, nature’s power lies in absence — no roars in the night, no giant footprints in the mud, no apex predator stalking its prey.

And perhaps that is Lombok’s most profound lesson in evolution, life is shaped not only by what exists, but also by what does not. The Wallace Line and the deep waters of the Lombok Strait do more than divide continents — they divide two entirely different worlds of life. (Sulung Prasetyo)

Read also: