Mesoscale transect sampling of trees in the lomako–yekokora interfluvium, democratic republic of the Congo

We conducted a mesoscale transect sampling of trees 10cm DBH in the Lomako–Yekokora interfluvial forest, Democratic Republic of the Congo. Our objective was to characterize the forest landscape contained between the Lomako and Yekokora rivers in terms of its floristic composition and to investigate how representative the Lomako study site, the location of a long-term study of primates, was of the entire forest block. Fifteen transects were laid out at seven sample stations placed approximately 10km apart and alongside a 70km trail running from the Lomako study site to the margins of the Yekokora river. Three transects totaling 3.65ha were laid out at the Lomako study site and two transects totaling 2ha at each of the remaining six sample stations, amounting to 15.65ha in total. Average DBH, tree density, tree species richness and floristic composition were determined for each transect. There were 5353 trees 10cm DBH in the total sample, representing 150 species in 35 families. Caesalpinoideae trees dominated the sample followed by Olacaceae and Annonaceae. Four forest types were identified: mixed primary (57% of the sampled plots), secondary forest (9%), Gilbertiodendron (22%), and swamp (12%). The seven sample stations differed from each other in average DBH, tree density, tree species richness and floristic composition. Most of the difference, however, was due to the fact that the four forest types were not equally represented at each sample station. When forest types were contrasted independently, a marked difference in average DBH, tree density, tree species richness and floristic composition was recorded. Conversely, when only mixed primary forest was analyzed across the sample stations, no significant difference was detected except for average DBH. Thus the Lomako study site is representative of the forest landscape contained between the Lomako and Yekokora rivers only when the different forest types are treated separately. The sample stations (including Lomako) differ from each other, however, in the proportional contribution of each forest type.     

How did bonobos come to range south of the congo river? Reconsideration of the divergence of Pan paniscus from other Pan populations

While investigating the genetic structure in wild bonobos,¹ we realized that the widely accepted scenario positing that the Pleistocene appearance of the Congo River separated the common ancestor of chimpanzees (Pan troglodytes) and bonobos (P. paniscus) into two species is not supported by recent geographical knowledge about the formation of the Congo River. We explored the origin of bonobos using a broader biogeographical perspective by examining local faunas in the central African region. The submarine Congo River sediments and paleotopography of central Africa show that the Congo River has functioned as a geographical barrier for the last 34 million years. This evidence allows us to hypothesize that when the river was first formed, the ancestor of bonobos did not inhabit the current range of the species on the left bank of the Congo River but that, during rare times when the Congo River discharge decreased during the Pleistocene, one or more founder populations of ancestral Pan paniscus crossed the river to its left bank. The proposed scenario for formation of the Congo River and the corridor hypothesis for an ancestral bonobo population is key to understanding the distribution of great apes and their evolution.