Indonesia is one of the world’s most remarkable regions for biodiversity. Positioned between Asia and Australia, the archipelago sits at the crossroads of two major biogeographical realms. This intersection creates distinctive patterns in the distribution of plant and animal species—patterns that scientists have studied for more than a century.
Two of the most important concepts in understanding these patterns are the Wallace Line and the Weber Line. Although both lines describe transitions in fauna, they serve different scientific purposes and offer insight into how evolution and geography have shaped Indonesia’s ecosystems.
- What Is the Wallace Line?
The Wallace Line, introduced by British naturalist Alfred Russel Wallace in the 19th century, marks a clear boundary between Asian and Australian fauna. Running between Borneo and Sulawesi, and between Bali and Lombok, the line highlights a striking shift in species composition.
To the west, species resemble those of continental Asia—such as tigers, elephants, and orangutans. To the east, the fauna begins to show strong Australian characteristics, including marsupials and unique birds like cassowaries.
This abrupt change exists despite the geographical closeness of the islands, illustrating how deep ocean trenches historically prevented species migration.
- What Is the Weber Line?
The Weber Line lies slightly east of the Wallace Line. Proposed by German zoologist Max Weber, this boundary represents the balance point between Asian and Australian species.
Unlike the Wallace Line—which indicates a sharp division—the Weber Line shows where neither group of fauna dominates. It forms a gradient zone, reflecting a biological blend across the islands of Wallacea, such as Sulawesi, the Moluccas, and parts of Nusa Tenggara.
This region contains some of Indonesia’s most unique species, including the Komodo dragon, anoa, and several endemic birds and reptiles.
- Why These Lines Matter
The Wallace and Weber Lines are more than geographic curiosities—they explain how Indonesia became one of the world’s megabiodiversity hotspots. Understanding these boundaries helps scientists:
Track species distribution across islands
Study evolutionary pathways shaped by isolation
Identify conservation priorities
Understand historical plate tectonics and sea-level changes
These lines remain essential tools in modern biogeography and conservation planning.
- Species Examples Across the Boundaries
Western Indonesia (Asian Influence)
Tiger
Elephant
Orangutan
Eastern Indonesia (Australian Influence)
Cassowary
Tree kangaroo
Cuscus
Wallacea Region (Transition Zone)
Komodo dragon
Anoa
Various endemic bird species
This diversity reflects the intersection of two evolutionary worlds—each bringing a unique ecological character.
- Key Insight: A Meeting Point of Two Worlds
Indonesia’s position between two continental shelves makes it a natural laboratory for studying evolution, migration, and biodiversity. The Wallace and Weber Lines reveal how geographic barriers, ocean depths, and ancient landmasses shaped the living landscapes we see today.
The coexistence of Asian and Australian species—combined with the presence of numerous endemics—makes Indonesia one of the most biologically rich regions on Earth. For researchers, conservationists, and nature enthusiasts alike, these biogeographical borders continue to offer valuable insights into the past and future of life in the archipelago.