When we set out on the first explorations in 2007 we expected to find 9 species of primates in the 30,000 km2 that we called the TL2, an area or landscape of central Congo that includes the middle-Lomami watershed and parts of the bordering Tshuapa and Lualaba (Congo) basins.
Our list of nine species was surmised from distributions given in field guides and published in scientific work. TL2 was thought to be moderately interesting for primates, but definitely NOT exceptional. That proved to be a major misinterpretation.
In fact within the first year we found a new species, the Lesula, Cercopithecus lomamiensis, a monkey that spends much of the time on the ground, unusual for a rain forest guenon. Genetic and morphological studies confirmed that it was distinct from its closest sister species, C. hamlyni.
In 2014 we had another surprise. A small monkey was hung for sale in Bafundo a village where we had one of our base camps. Our teams did not recognize this monkey either. Locally it was given the name Inoko. Indeed John confirmed that there was no monkey in the field guide with the prominent rufous color around the face. Other characters seemed to place it most closely to the representation of the Cercopithecus dryas monkey.
A student who had visited the TL2, Christina Bergey, sent a photo of the dryas monkey in a comment to our blog post about the new mystery monkey. The photo was taken by Russ Mittermeier, on a trip for CI (Conservation International) to the Wamba-Kokolopori forest, the only area where C. dryas is known to exist. The monkey in the photo did indeed have a rufous trim around the black face, although not in the field guide. Soon afterwards, the scientist who first discovered the dryas monkey in the Wamba-Kokolopori, Suehisa Kuroda, added another comment on the blog. Yes, our photo looked to be the same animal that he had found.
Since the original discovery, we have found C.dryas in a second location 30 km to the west of Bafundo, near the Lomami River and actually in the Lomami National Park. But how do we explain the 400 km of continuous forest and without known C. dryas that separate the TL2 population and the Wamba-Kokolopori population?
So the list of 9 has been expanded to 11 species of anthropoid primates (apes and monkeys) in the TL2. These are now known to include 13 distinct taxa (i.e. species and subspecies).
The Lomami River itself seems an arbitrator for the diversity. The Lesula for instance is only on the west bank of the Lomami
There is also one species of red colobus on the west bank (Piliocolobus tholloni) and another on the east bank (P. parmentieri).
Even the bonobo population on the east and west bank is amazingly different. The laboratory of Takeshi Furuichi found that the bonobos on the east bank of the Lomami are genetically distinct from all those found farther to the west.
The Lomami also seems to be an important divide for two Cercopithecus wolfi subspecies, as well, although intermediate forms have been found close to the Lomami River.
Interestingly, it is not only primates that split along the Lomami. The Okapi is known on the west bank of the Lomami, but then is absent east of the Lomami all the way to the Lualaba. It shows up again in the forests to the east of the Lualaba.
Not all the patterns of TL2 primate diversity are so geographically distinct.
Even the red-tailed monkey has phenotypic variation that we have not been able to describe geographically.
This blog-post is adapted from John Hart ’s presentation at the International Primate Society conference in Chicago in August of this year. He included a comparison of the primate fauna of the Ituri Forest with that of the Lomami Forests. Though both areas are rich in primates – the patterns of diversity are very different.
It was the bonobo and the forest elephant that gave the first urgency to create the Lomami National Park : an important range extension for the bonobo and a substantial, but isolated population of forest elephants. Both were threatened by hunting. But it is the primate discoveries that are revealing the mystery of these forests along the Lomami River and that are revealing the need for continued exploration and strong protection.