Chimpanzees in the Issa Valley, Tanzania.
Photo credit: P. Gagneux/GMERC.

An international team of researchers are predicting a massive decline in the ranges of Africa’s great apes by 2050 because of the impacts of climate change, land-use changes, and human population growth. They say the greatest loss will be in unprotected areas.

The authors of a new report write: “We predict that massive range loss is likely to occur in the next thirty years, but range gain is more uncertain given that African apes will not be able to occupy these new areas immediately due to their limited dispersal capacity, migration lag, and ecological constraints.”

The researchers say their results corroborate other recent studies showing that African ape populations and their habitats are declining dramatically.

“Our findings suggest that some of the negative effects of climate change on African apes can be mitigated if appropriate land use planning and management action is taken,” Joana S. Carvalho et al. write.

Most African apes live outside of protected areas. They have a low dispersal capacity due to their small population sizes, low population densities, dietary requirements, and poor thermoregulation.

All African great apes are classified on the International Union for Conservation of Nature’s Red List of Threatened Species either as endangered (mountain gorillas, bonobos, Nigeria-Cameroon chimpanzees, eastern chimpanzees, and central chimpanzees) or critically endangered (Cross River gorillas, Grauer’s gorillas, western lowland gorillas, and western chimpanzees). All are regarded as flagship species for conservation.

“Given that most future range changes are predicted outside protected areas, Africa’s current protected-area network is likely to be insufficient for preserving suitable habitats and maintaining connected ape populations,” Carvalho et al. write in the new report, which was published in the journal Diversity and Distributions on June 6.

“Thus, conservation planners urgently need to integrate land use planning and climate change mitigation measures at all decision-making levels both in range countries and abroad.”

Fiona Maisels from the Wildlife Conservation Society (WCS), who is a co-author of the new report, said: “As climate change forces the different types of vegetation to essentially shift uphill, it means that all animals – not only great apes – that depend on particular habitat types will be forced to move uphill along with the vegetation, or become locally extinct.

“When the hills are low, many species, great and small, will not be able go higher than the land allows, and huge numbers of animals and plants will simply vanish.”

Joana Carvalho, who is a postdoctoral researcher in the Faculty of Science, Liverpool John Moores University in Britain, added: “Massive range loss is widely expected outside protected areas, which reflects the insufficiency of the current network of protected areas in Africa to preserve suitable habitats for great apes and effectively connect great ape populations.”

The authors of the new report quantified the joint effects of climate, land-use, and human population changes across African ape ranges by 2050, considering the best- and worst-case scenarios.

‘Best case’ implies slowly declining carbon emissions, with appropriate mitigation measures put in place. ‘Worst case’ assumes that emissions continue to increase unchecked.

In the best-case scenario, Carvalho et al. predict that great apes will lose 85 percent of their range overall. In the area outside national parks and other areas protected by legislation, the loss would be 50 percent.

In the worst-case scenario, the researchers predict a 94 percent loss of range overall and a 61 percent loss in areas that are not protected.

“Range gains are predicted outside protected areas if dispersal occurs – 52% in the best-case scenario and 21% in the worst,” Carvalho et al. said.

The researchers added that an increase in range gain was expected across the study regions (66% in the best-case scenario and 24% in the worst). More than half of range losses and gains are predicted to occur outside protected areas, in areas where the ranges of multiple species overlap.

Carvalho et al. explain that range gain and loss are processes that operate at very different time scales and great apes can be expected to take hundreds to thousands of years to disperse into new suitable areas.

“The 30-year time frame considered here represents a bit more than an ape generation and it is unlikely that migration into new areas during this time occurs to any greater extent,” the researchers write.

“It is therefore very important that these results are not interpreted as indicating that range gain will definitely occur as effective protection of new suitable areas will need to be ensured for a great ape population to shift to such habitat.”

A ‘central chimpanzee’¹. Photo credit: Emma Stokes/WCS.

The researchers compiled information held in the IUCN Species Survival Commission’s A.P.E.S. database, a repository that holds a wealth of information about the population status and conservation of great apes and the threats they face. The information relates to several hundred sites and has been collected over twenty years.

The authors of the new report explain that mountains are currently less suitable than lowland areas for some great ape species.

“However, climate change will render some lowlands less suitable – warmer and drier, with perhaps less food available – but the nearby mountains will take on the characteristics that those lowlands currently have,” Maisels said.

“If great apes are able to physically move from the lowlands to the mountains, they may be able to survive, and even increase their range, depending on the species, and whether it is the best- or worst-case scenario. However, they may not be able to travel (disperse) away from the lowlands in the time remaining between today and 2050.”

Carvalho et al. argue that effective conservation strategies require careful planning for each species that focuses on both existing and proposed protected areas.

They say that efforts to maintain connectivity between the habitats predicted to be suitable in the future will be crucial for the survival of African apes.

The researchers cite the example of the country-wide approach undertaken in Gabon, where planning for the development of agriculture, road and rail links, and mineral extraction has been informed by wildlife and vegetation data in order to locate these activities in areas that are already degraded, and to avoid closed-canopy old-growth and remote forests.

“This will be an effective way of promoting habitat connectivity to maintain African ape populations and sympatric wildlife,” Carvalho et al. write.

Maisels says the new study highlights the need for urgent action to combat both biodiversity loss and climate change.

“Governments must protect and conserve the habitats of great apes – where they are now, and where they will need to move,” she said.

Carvalho and her co-authors say governments attending the upcoming Convention on Biological Diversity CoP 15 in September and the UN Climate Change Conference in November should adopt meaningful commitments to protect and conserve great apes and their habitats and combat climate change.

Hjalmar Kuehl from the German Centre for Integrative Biodiversity Research (iDiv) in Leipzig, Germany, who is one of the new report’s authors, said: “There must be global responsibility for stopping the decline of great apes. Global consumption of natural resources extracted from ape range countries is a major driver of great ape decline.

“All nations benefitting from these resources have a responsibility to ensure a better future for great apes, their habitats and the people living therein by developing more sustainable economies.”

The new study involved more than sixty co-authors from numerous academic and non-academic organisations and government agencies, including the Max Planck Institute for Evolutionary Anthropology in Germany, the University of Stirling in Scotland, the Antwerp Zoo Society in Belgium, the Born Free Foundation, the Chimbo Foundation in the Netherlands, the Conservation Society of Sierra Leone, Fauna & Flora International, the Frankfurt Zoological Society, West African Primate Conservation Action, the University of Burundi, the Jane Goodall Institute, and other establishments and organisations in Ghana, Cameroon, the US, France, Gabon, Liberia, Guinea, the Central African Republic, Tanzania, Italy, Japan, and Switzerland.

1. The central chimpanzee or tschego (Pan troglodytes troglodytes) is a chimpanzee subspecies. Central chimpanzees live mainly in Gabon, Cameroon, and the Republic of the Congo, but also, to a lesser extent, in other regions.

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