 few groups studying Nigeria-Cameroon chimpanzees in the wild, collected fecal and hair samples for genetic analyses. They also mapped the precise locations of those sample collection sites in addition to locations of reports of chimp sightings and evidence of activity including nests and tools.
“The Nigeria-Cameroon chimpanzee is perhaps the least studied of all chimpanzee subspecies,” said Paul Sesink Clee, a doctoral candidate in Gonder’s lab, who was first author of a paper detailing habitat distribution and modeling impacts of climate change. “This is the first time that their distribution and habitat has been studied in such detail, and the data used to predict how their habitats might degrade under climate change.”
Where Distinct Ecosystems Meet, An Unexpectedly Different Population of Chimps Occurs
Central Cameroon is noteworthy not just as a place where two chimp subspecies meet. It’s also the place where the species-rich, mountainous Gulf of Guinea region abuts the distinct, but comparably diverse, lowland Congo River Basin. Together, these two ecosystems contain about 20 percent of all plant and animal species on the entire planet, and many of those species are endemic—found only here in central Africa.
Habitat Types and Chimpanzee Population History in Cameroon and Nigeria. Credit: Sesink Clee et al.
These different rainforest ecosystems converge with savanna in central Cameroon forming a savanna-woodland mosaic known as an ecotone.
“This ecotone is associated with driving diversification in a lot of different species,” Mitchell said. Ecotones are thought to be important in driving variation and diversification of species all over the world.
This particularly fragile savanna-woodland mosaic habitat in central Cameroon north of the Sanaga River is where Mitchell’s genetic analysis identified a population of Nigeria-Cameroon Chimpanzees that was distinct from those living in the mountainous rainforests of northwest Cameroon and eastern Nigeria. They also determined that the population in the ecotone diverged from the western rainforest population about 4,000 years ago —while still remaining closely related members of the same subspecies. (In contrast, this subspecies as a whole diverged from the Central Chimpanzee subspecies (Pan troglodytes troglodytes), whose populations live in Congo River Basin forests south of the Sanaga River, about 200,000 years ago or more.)
In subsequent modeling in a second paper, Mitchell and colleagues concluded that in the Nigeria-Cameroon chimpanzee, a significant amount of genetic difference could come from adaptation to different environments.
In short, these chimps have changed in distinct, genetically noticeable ways, to their lives in different habitats.
Environments Threatened by Climate Change
Yet the habitats these chimps rely on may be particularly threatened, the team’s analysis has showed.
“We were surprised to see that the Nigeria-Cameroon chimpanzees living in the savanna-woodland habitat of central Cameroon are under the most immediate threat of climate change, and may completely lose their habitat within our lifetime,” said Sesink Clee.
Drexel University researchers Paul Sesink Clee (seated) and Matthew Mitchell (standing, center) analyzing climate data from a field site with researchers from Ebo Forest Research Project. Credit Mary Katherine Gonder
He and colleagues reached this conclusion based on combining detailed chimpanzee location data with the environmental characteristics of these locations. They then predicted how these habitats would change under climate change scenarios for years 2020, 2050, and 2080. The scenarios were provided by the UN’s Intergovernmental Panel on Climate Change and considered a varying range of factors including use of fossil and non-fossil fuels, human population growth, and environmental protection efforts.
While the team predicted little change in the mountainous rainforest habitat, the ecotone habitat of the second population was predicted to decline quickly under all scenarios by the year 2020 and could disappear almost entirely