Monday, March 24, 2014

Pongo, the weird cousin in the great ape family

Last post I talked about the differences between Bornean and Sumatran orangutans. But what makes orangutans different from all the other great apes? There are 4 extant great ape genuses: humans (Homo), chimps (Pan), Gorillas (Gorilla), and Orangutans (Pongo). Out of all these, the orangutans split off from the rest the earliest, and are genetically the least related to humans. In many ways, they are the weirdest of the great apes!

To start, they are the only remaining ape species native to Asia. All the other great apes are found only in Africa (except for humans, which today are a global species – but we originally evolved in Africa). Note that I say ‘remaining’ ape species. Millions of years ago, apes were rampant across the old world, including many species in Asia. At some point, most of these species went extinct, and only the orangutan and gibbon line survived the present day.  Were any of these species ancestral to orangutans, and if so which ones? No one really knows for sure, but some of the skeletal remains we have found in Asia show some morphological similarities to Orangutans. Search Sivapithecus if you want to find out more. Interestingly, there was a gigantic species of ape called Gigantopithecus living in Asia until fairly recently (and by fairly recently, I mean thousands of years ago). Humans were already around, and may have run into this other ape creature – in fact, some people think this may be the origin of the ‘Yeti’ or ‘Sasquatch’. Maybe when humans and Gigantopithecus coexisted long ago, humans lived in fear of this creature and shared stories to each other about it; through the retelling of these stories from generation to generation, the creature survived in our memories and into legend, even after it became extinct. Of course, there are always those who insist bigfoot/yeti/sasquatch hasn’t gone extinct, but let’s not get into that. 

Orangutans are the most arboreal of the great apes. Chimpanzees, Bonobos and Gorillas spend a lot of their time in trees, but they also spend an extensive amount of time on the ground, where they move around by knucklewalking. This is probably a big reason why orangutans have been the least studied great ape; it’s a lot harder to find them, follow them, and take date on them, if they’re constantly up high in the branches, out of view. Humans are obviously the least arboreal of the five species of great ape, given that we’re bipedal and spend virtually all of our time on the ground. Orangutans however, spend almost all of their time up in the trees. They are very well adapted for it, having long arms and long legs for reaching across gaps to grab branches, and they have very long fingers and opposable thumbs on both hands and feet, which allows them to firmly grasp the branches and trunks they use to move around.  It’s almost like the have four hands rather than two hands and two feet, allowing them to have multiple points of contact to the trees that they use to move around, which makes it safe for them to be up so high. 

They are masters at this kind of locomotion, being able to ‘polevault’ from tree to tree by bending the trunks and swinging to an adjacent tree, as well as brachiating their way throughout the canopy. Primatologists who study orangutans have traditionally thought that only the flanged males come to the ground often; however, a recent study which used a collection of camera traps distributed over a study site, found that all age-sex classes of orangutans come to the ground fairly often. Personally, I’ve seen females come down to the ground as well, but only a handful of times (and one of the females was traveling together in consortship with a flanged male, so perhaps she felt safe enough in his presence to come down). We still don’t know if this is a universal thing among all groups of orangutans, or something that varies from site to site…maybe they all do this, but just not often in the presence of people. This just shows that there is still a lot to learn about orangutan behavior.

In contrast to all of the other great apes, which are extremely social creatures with complex social dynamics and networks, orangutans spend the majority of their time alone. They do interact with other individuals from time to time, so they could be described as solitary but social. There is not much long-term social bonding. Usually mothers and their offspring will remains in association for a long time, and will overlap in home range, but eventually their social bonds weaken and they end up living independent lives. The relationship seems to last longer with daughters, as male offspring will usually migrate out of their home range into a new area. The consequence of this is that in a particular area, a lot of the females will be related, but few of the males are. Often times we see that when orangutans form a party (which is the technical term for when two or more orangutans interact and travel with each other during the course of a few hours, a day, or longer), they are all female and related.  Sociality also depends vastly on fruit availability. If fruit availability is low, they will tend towards solitude to avoid competition. If fruit availability is high, they will aggregate in the feeding trees more often and tolerate each other’s presence; there is enough food to go around and the benefits of social interaction outweigh the costs of sharing the food supply. Of course, all of these facts is what we has been traditionally written about in the orangutan literature. 
More recently, researchers are starting to find that perhaps orangutans are more social than we think. Definitely not as social as other apes, but sociality is still a very important part of orangutan dynamics. 

Flanged males (If you’re wondering what flanged males are, I’ll explain it in the next post!) prefer traveling alone, unless they are in consortship with a female; they do not under any circumstances associate with any other males, and will get aggressive upon encountering others. Unflanged males tend to avoid other males, but sometimes they will form bachelor squads with other unflanged males. 

This is just the tip of the iceberg when it comes to orangutans. What I mentioned before about flanged/unflanged males is a very interesting dynamic among orangutans, and I’ll be diving down into that on the next post. 

1 comment:

  1. Robert, thanks for representing us there and for these posts so interesting. God bless you! I am proud of you. Att. A proud puertorrican/ boricua.