Indonesia is recorded as the country with the highest number of mammal species in the world. According to the Mammal Diversity Database managed by the American Society of Mammalogists (December 2025), Indonesia has 777 documented mammal species, slightly more than Brazil with 776 species and China with 710 species.
Overall, Indonesia’s mammalian diversity consists of 793 extant species and 4 extinct species, distributed across 17 orders, 58 families, and 241 genera. This list excludes domesticated species as well as species with very wide global distributions, while extinction status is calculated based on records from the last 500 years.
So, what makes Indonesia home to such an extraordinary number of mammals?
Archipelagic Nation: Isolation That Generates New Species
Indonesia’s structure as an archipelagic country is a key factor. Comprising more than 17,000 islands, Indonesia’s landscapes create thousands of separated habitats. Geographic isolation over long evolutionary periods has allowed mammal populations to evolve independently, leading to the formation of new species.
Island biogeography theory explains that large islands located close to major landmasses tend to have high species colonization rates, while smaller and more isolated islands experience higher natural extinction rates but also exhibit high levels of endemism. This pattern is clearly visible in Indonesia.
Western regions such as Sumatra, Java, Bali, and Kalimantan possess high species richness because they were once connected to mainland Asia. In contrast, eastern regions, which are more isolated, are home to many unique species found nowhere else in the world.
However, island isolation also makes ecosystems more vulnerable. Data show that 93 percent of bird species recorded as extinct since 1600 originated from islands. This pattern is highly relevant for understanding the risks faced by Indonesia’s wildlife.
A Natural Transition Zone
The second key factor is geological history. Indonesia lies at the convergence of three major tectonic plates: the Eurasian, Philippine, and Australian plates. This unique position divides Indonesia into three major biogeographic regions: Sundaland, Wallacea, and Sahul.
Western regions such as Sumatra, Java, Bali, and Kalimantan sit on the Eurasian Plate and were once connected to mainland Asia. This connectivity enabled large-scale migration of Asian mammals into the region.
In contrast, Papua and West Papua lie on the Sahul Shelf, which has strong geological ties to Australia. When sea levels were lower around 19 million years ago, this area was connected to Australia, allowing species to move freely between the two landmasses.
Between these zones lies Wallacea, encompassing Sulawesi, Maluku, and Nusa Tenggara. This region serves as a transitional zone, containing a mixture of Asian and Australian elements as well as a high number of unique species.
Sulawesi offers the clearest example. The island is a hotspot for endemic small mammals, particularly rodents (Muridae and Sciuridae) and shrews (Soricidae). Many species in this region are classified as threatened, Data Deficient, or only recently described, meaning scientific research remains limited.
Biodiversity Under Threat
Indonesia’s land area accounts for only about 1–1.3 percent of the world’s total land surface. Yet it harbors approximately 12 percent of the world’s mammal species, 10 percent of plant species, and 17 percent of bird species.
Indonesia also contains the third-largest tropical rainforest area in the world, after the Amazon and the Congo Basin. These forests serve as critical habitats for orangutans, Sumatran tigers, Javan rhinoceroses, and many lesser-known species.
This concentration of biodiversity is matched by intense pressure. Indonesia leads the world in the number of endemic mammal species, while also having the highest number of threatened mammals.
FAO data record net forest loss of around 684,000 hectares per year between 2010 and 2015, driven primarily by agricultural expansion, plantation development, and timber and mineral extraction. Land clearing through burning, particularly for oil palm plantations, has accelerated habitat degradation.
Indonesia also faces additional risk factors in the form of volcanic activity and earthquakes. The country has 76 active volcanoes, the highest number globally. Disasters such as volcanic eruptions, tsunamis, and landslides have direct impacts on ecosystems and wildlife populations.
At the same time, the Ministry of Environment estimates that more than half of Indonesia’s species have yet to be scientifically documented. This suggests that the figure of 777 mammal species may not fully reflect the country’s true biological potential.
The high number of mammals in Indonesia is not the result of a single factor, but rather a combination of its archipelagic nature, geological history, biogeographic transition zones, and vast tropical forests. The data confirm Indonesia as one of the world’s primary centers of mammalian biodiversity, along with conservation challenges of equal magnitude.
Source:
- https://www.mammaldiversity.org/country/ID/
- https://www.ifaw.org/projects/protecting-indonesias-endangered-wildlife
- https://www.ran.org/indonesia_s_rainforests_biodiversity_and_endangered_species/
- https://www.cambridge.org/core/journals/oryx/article/conservation-status-and-priorities-for-sulawesis-unique-small-mammal-fauna/A62EBE457E255E9E8AE3B4F0F4D8D667
