The Wildlife of Sulawesi, Wallace’s Anomalous Island

The Galapagos Islands are renowned for how their exceptional flora and fauna influenced Charles Darwin in deriving his theory of evolution by natural selection. However, far less know is the island of Sulawesi, which impacted another British naturalist, Alfred Russel Wallace, who independently discovered the same mechanistic explanation for the then-termed transmutation of species.

Like Darwin, Wallace was a British naturalist who made many important discoveries and observations during prolonged explorations of then-remote areas of the world. Wallace was one of the first naturalists to investigate the Amazon Basin, which increased his renown among naturalists, including Charles Darwin. However, he made his most important findings on an eight-year exploration of the Malay Archipelago, which exists between mainland Indochina and Australia, and is comprised of the nations of Brunei, Singapore, Malaysia, Indonesia, the Philippines, and East Timor.

Wallace discovered that across the Malay Archipelago, the western islands contain species similar to those found in mainland Asia, such as tigers, rhinoceroses, and apes, while the eastern islands feature species characteristic of Australasia, such as marsupials and Eucalyptus trees. Wallace determined that this trend is centered on a divide located within the Makassar Strait between the islands of Sulawesi and Borneo, which was later coined the Wallace Line. Given these findings, Wallace is now considered the father of biogeography, the study of the distribution of species across space and time.

Through his exploration of the Malay Archipelago, Wallace was impacted particularly by observations made on the Indonesian island of Sulawesi, then called Celbes, which he referred to as “the anomalous island.” Wallace’s name for Sulawesi reflects its unique assemblage of species, which is the product of its complex geological history. While Sulawesi exists east of the Wallace Line, it is unique in that it features species of both Asian and Australasian origin. For example, it is the only place on the planet where both marsupials and old world monkeys are found.

Today, Sulawesi and a group of surrounding islands have been recognized as a global biodiversity hotspot. This biodiversity hotspot, known as Wallacea, contains a high number of endemic species, which include over 1500 species of plants, 127 mammals, 274 birds, 99 reptiles, 40 birdwing butterflies, 33 amphibians, and 50 freshwater fishes.

Sulawesi is the largest island within the complex, and contains more than half the total area of pristine terrestrial and marine habitats across Wallacea. It also hosts the largest proportion of imperiled species within the hotspot, featuring 448 of the 569 IUCN Red List Species present throughout Wallacea.

Wallace noted the high rate of endemism on Sulawesi. In some cases, this made it difficult for him to determine the taxonomy of a given species. For example, the taxonomic classification of the anoa, a small bovine endemic to Sulawesi, had generated controversy as to whether it be classified as an ox, buffalo, or antelope. The anoa include two species, the mountain anoa (Bubalus quarlesi) and the lowland anoa (Bubalus depressicornis), which differ in habitat and appearance, with both now considered as Endangered.

In addition to the anoa, Sulawesi features a number of other incredible endemic mammal species, many of which are also imperiled.

Babyrousa is a genus of pig-like animals, comprised of four species which are endemic to Wallacea. The most widespread and abundant species is the North Sulawesi babirusa (Babyrousa celebensis), which is considered Vulnerable by the IUCN. The babirusa, whose name means “pig-deer,” is a curious creature, with two immense tusks, each curving backward from the snout towards the eye.

The bear cuscus (Phalangista ursina) is a strange-looking arboreal marsupial that lives in the of tropical rainforests of Sulawesi. While the habitat and nocturnal lifestyle of this species makes it natural history poorly understood, it has been designated as Vulnerable by the IUCN due to an apparent population decline.

The crested black macaque (Macaca nigra) is an old world monkey that inhabits the rainforests of northwest Sulawesi. This is a relatively small species of macaque, which typically weights between 3.6 and 10.4 kg, is largely terrestrial spending up to 60% of its day on the ground foraging for food. It is a highly social species, typically living in groups of typically five to twenty-five animals. The crested black macaque is highly imperiled, as it is considered critically endangered by the IUCN.

The spectral tarsier (Tarsius spectrum) is another primate species endemic to Sulawesi. It is incredibly tiny, typically weighing between only 102 and 130 grams! It is nocturnal, and uses its large eyes to forage for insect and small vertebrate prey throughout the canopy. This species is listed as Vulnerable by the IUCN. These species are threatened primarily by habitat loss.

Over the past few decades, Indonesia has undergone massive amounts of deforestation, including the destruction of immense areas of primary forest. According to some estimates, the rate of forest loss in Indonesia has surpassed that of the more covered Brazilian Amazon. Sulawesi is no exception, having lost large amounts of primary forest. According to a 2014 study that measured rates of primary forest loss across Indonesia from 2000 to 2012, during that period, Sulawesi lost 7.1%, 15.6%, and 2.7% of its lowland, wetland, and upland primary forests, respectively. These losses accounted for a total loss of 396 kha of primary forest.

It is clear that the endemic species of Sulawesi represent a unique component of Earth’s biodiversity. Conservation efforts are underway to maintain and rehabilitate habitat on the island, and help the many imperiled species that live there.

If you would like to help the wildlife of Sulawesi, while following in the footsteps of Wallace, consider applying to WorkingAbroad’s Project with the Wildlife Rescue Centre in northern Sulawesi.

– By WorkingAbroad Blog Writer Sean Feagan

Images from Wikimedia Commons