Featured image credit: Orangutan by ghatamos, CC BY 2.0 via Flickr.
Dr Adam J. Munn is researcher based at The University of New South Wales, Australia.
Dr Mark E. Harrison is Co-Director of the Borneo Nature Foundation and is based at the University of Leicester.
Conservation Physiology publishes research on all taxa (microbes, plants and animals) focused on understanding and predicting how organisms, populations, ecosystems and natural resources respond to environmental change and stressors.
Image credit: Flanged male orangutan. Copyright Dr Esther Tarszisz.
Image credit: Dr Esther Tarszisz planting seeds clean from orangutan poo. Image copyright Borneo Nature Foundation.
The movement of seeds from their parent tree is key to mapping seed dispersal patterns, but as well as noting seed spitting, we need to know when and where orangutans poo. To that end we followed wild orangutans habituated to humans over several seasons, noting where and when they fed, and more importantly, where they pooped! We combined this data with measures of the passage of artificial seeds (plastic beads) through captive orangutan at Australia’s Perth and Taronga zoos. We did this by training captive orangutans to swallow our seed mimics and then, you guessed it, we collected their poo. Overall, we found that plastic “seeds” took an average 70-90 hours to pass through the orangutan, and up to 120 hours to be completely eliminated. Thus, in terms of mapping the potential dispersal of seeds by orangutans, we showed that fecal deposition, or poo points, from where seeds were initially ingested lagged behind the actual animal movement by 3-5 days. This has several key implications for the forest structure and establishment of new plants. Female orangutans tended to be more centric in movements driven by food sources, but males roamed widely for food and mates. This suggests that seed dispersal implications of males and females may be very different, but critical for the maintenance of centrally located fruits as well as those spread more broadly to support wandering males.
In Central Kalimantan, orangutans are vital for the health and well-being of their tropical peatland homes, and not just for their own survival. Indonesia’s tropical peat swamps are massive carbon sinks, trapping up to 20% of the earth’s soil carbon. These swamps already face enormous challenges from clearing, peat drainage for agriculture and timber extraction, and subsequent fires. In 2015 alone, these activities released 0.89 – 1.29 gigatons of carbon dioxide equivalent from Indonesia’s peatlands. Crucially, collapse of these peatland ecosystems would see the release of gigatons of carbon to the atmosphere, comparable with thousands of years of this stored peat carbon being released in just decades; a Gaian “burp” of titanic proportion, and consequence.
Image credit: Mother and young orangutan. Copyright Dr Esther Tarszisz.
Orangutans are the largest tree-dwelling frugivores (fruit eaters) in the world. They eat leaves, flowers, some invertebrates, and may even scavenge meat on occasion, but they are primarily fruit eaters, being especially attracted to the energy-rich fruits of the biggest forest trees. While other large animals, such as elephants and rhino, are capable of spreading seeds from fallen fruits, orangutan are capable of spreading the seeds from the hanging fruits of the largest trees, making them critical for forest production and regeneration.
Orangutans quite literally are “persons of the forest,” at least according to their Malay name (orang means “person” and hutan is “forest”). But this is more than just a name. As well as their distinctively “human” qualities, these large charismatic fruit-eaters are also gardeners, forest engineers responsible for spreading and maintaining a wide array of tree species. In Borneo in particular, their role as ecosystem engineers is not simply aesthetic, they may be critical for mitigating global carbon emissions. But how exactly might orangutans do this? The answer is in their poo.
After many hours following and watching wild orangutans it is hard to deny their human-like mannerisms. What is clear is that these “persons of the forest” may be vital for the preservation of Indonesia’s massive global carbon stores. But orangutans continue to be threatened by legal and illegal land clearing, as well as hunting. This needs global attention, and further declines, or worse extinction, of these charismatic forest gardeners may reflect a grim rehearsal of our own demise, unless we pay attention and take action now, before the poop really hits the fan!
To find out just how important orangutans are for these peatland forests, we collected over 200 individual poo samples from wild orangutans in Central Kalimantan. Poo samples were washed and the seeds collected and germinated in a local nursery, alongside those extracted by us from intact fallen fruits. We found 13 species of undamaged types of tree seeds in orangutan poo, ranging in length from <1cm to >2cm. Most of these germinated more successfully than the seeds we physically extracted from whole fruits. However, in addition to seeds from poo samples, we collected seeds that were spat to the ground by orangutans during feeding. Curiously, these spat out seeds had the highest germination success, especially for the very largest seeds (> 20 mm). The importance of the higher germination success of seeds spat by orangutan has hitherto been overlooked, but could be enormously important for the dispersal of the largest forest trees, as fruits can be carried considerable distance from a parent tree before the remnant seeds are ejected to the ground.
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In the wild, the orangutan lives a semi-solitary existence. Infants and youngsters travel with their mothers, and adult males, who have nothing to do with the raising of offspring, tend to travel long distances on their own. This solitary existence is determined by the distribution of their food sources. In Sumatra, where fruit is in more abundance, orangutans enjoy a slightly more social existence, congregating on more occasions when there are mast fruitings. And in Sumatra, scientists have documented numerous examples of culture amongst orangutans, the spread of which is perhaps made possible by this more social lifestyle. The largest arboreal mammal on the planet, the orangutan makes nests high in the forest canopy, sometimes incorporating leafy roofs to keep out the rain in rainy season. (They also use enormous leaves as umbrellas! ) The forest canopy is their home; there, they find all their food, avoid predators, travel along aerial highways and even give birth. And as much as the orangutan needs forest, the forest needs the orangutan. The orangutan serves as a major seed distributor. Using their strong jaws, they can open fruits that other animals cannot, and many seeds pass through their gut undigested. Some of these seeds can only germinate when deposited in the dung of the orangutan. In their role as gardeners of the rainforest, they also are responsible for essential pruning. As they travel through the upper canopy, they break off branches, allowing the sunlight to reach the forest floor to permit new shoots to grow.
The name orangutan cames from the Malay “orang” meaning person and “hutan” meaning forest, so the orangutan is literally a “person of the forest.” The Dayak tribes of Borneo traditionally regarded the orangutan as a type of human, one that pretended to be mute so as to avoid being put to work. Indeed, the orangutan shares 97% of its DNA with humans, making it one of our closest relatives, and along with humans, chimpanzees, bonobos and gorillas, are one of the Great Apes. Other than humans, they are the only Great Ape living in Asia, and today are confined to the islands of Borneo and Sumatra. An orangutan infant typically spends from 7-9 years with its mother learning what it needs to learn about survival in the forest entirely from her. It is said that orangutans enjoy the strongest and longest mother-infant bond in the animal kingdom, with the exception of humans. This long learning period makes the orangutans one of the most intelligent animal species on the planet (Scientists continue to debate whether this accolade belongs to the chimpanzee or the orangutan.)
The single greatest threat to the survival of the orangutan is the conversion of their forest to agriculture and other degradation of their habitat. Therefore, the solution to ensure their survival is to minimize this impact on their habitat. In Indonesia, close to 80% of orangutans exist OUTSIDE of protected areas. And in both Malaysia and Indonesia, particularly in Sabah and Sarawak, Kalimantan and Sumatra, relatively new frontiers are being targeted for oil palm development, logging and mining. It just so happens that these are precisely the areas where the last wild orangutans on earth reside. In order to save these species, as well as the rest of the immeasurable biodiversity that shares their habitat, development must only proceed in the most sustainable way possible.
My research showed that orangutans are frequently dispersing a wide diversity of seeds throughout the forest. I will analyze the data back at Boston University to figure out which of these genera orangutans are dispersing most effectively. Orangutan dispersed seeds do germinate and often times a higher percentage of orangutan dispersed seeds germinated compared to the seeds collected directly from fruit. It appears that the act of an orangutan consuming and defecting a seed does actually help the seed germinate. Although orangutans do predate a portion of fruit seeds, for a different group of fruits orangutans are important seed dispersers.
I followed orangutans, analyzed their feeding behavior, and counted seeds defecated by orangutans for my dissertation research at Boston University. In addition to following orangutans, I also conducted germination experiments to test if seeds dispersed by orangutans would germinate better than seeds collected from fruits. Camera traps were valuable in helping me understand what other animals interact with seeds dispersed by orangutans. Sometimes rodents stash the seeds elsewhere in an act called ‘caching’ and sometimes other animals eat the dispersed seeds. Excitingly, I was able to do my research alongside Ahmad Rizal, an undergraduate student from Jakarta, who is also interested in understanding the ecological role of orangutans as seed dispersers.
Orangutans have powerful jaws and teeth adapted for crushing hard food objects. This selection of traits would suggest orangutans are crushing and eating seeds as a main component of their diet. Based on these observations orangutans have been labelled as ‘seed predators’. However, my research this year in Gunung Palung National Park tested an alternate hypothesis. I predicted that in addition to chewing up and destroying seeds, orangutans are also swallowing seeds intact and dispersing these seeds throughout the forest. Many species of primates that consume a large quantity of fruit are important seed dispersers, so I hypothesized that orangutans may similarly be dispersing viable fruit seeds.
Throughout my year at Cabang Panti Research Station I made many friends and had many great experiences. The help of the Cabang Panti’s research staff was invaluable to me. The field assistants assisted me with collecting behavioral data while following orangutans and the lab assistants helped with processing samples brought back from the forest. The many students, interns, volunteers, and managers were incredible to work with as well. I would not have had a successful research year without all of their help. I will miss my time and friends at Cabang Panti.