Greater Mahale Ecosystem

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Summary

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• Eastern chimpanzees (Pan troglodytes schweinfurthii) are present in the Greater Mahale Ecosystem.
• It has been estimated that 2,600 individuals occur in the site.
• The chimpanzee population trend is decreasing.
• The site has a total size of 20,000 km².
• Key threats to chimpanzees include human settlements in important habitat, logging and charcoal production, fires, expansion of agriculture and herding, and poaching.
• Conservation activities have focused on anti-poaching patrols and presence of researchers, and providing fuel-efficient ovens.
• The site holds approximately 90% of the chimpanzee population in Tanzania.

Site characteristics

Located in western Tanzania, the Greater Mahale Ecosystem includes the Mahale Mountains National Park and its surrounding natural habitat. In addition to the eastern chimpanzee, other species of conservation concern that occur in the area include red colobus monkeys, elephants, lions, sables, and the endemic bird Kungwe apalis (WCS). A total of 1,939 mammal, bird, reptile, amphibian and plant species have been recorded at the site, of which 15 species are endemic to the Albertine Rift and 28 species are threatened (CR, EN, VU) under the IUCN Red List (WCS).

Table 1. Basic site information for Greater Mahale Ecosystem

Species	Pan troglodytes schweinfurthii
Area	20,000 km²
Coordinates	Lat: -5.861672 , Lon: 30.357929
Type of site	Non-protected area
Habitat types	Subtropical/tropical montane forest, Grassland
Type of governance	Governance by government

Types of sites Governance types Habitat types

Ape status

The WCS Albertine Rift Program conducted surveys of the Greater Mahale Ecosystem in the mid 2000s with Jane Goodall Institute (JGI), to estimate chimpanzee numbers for the area and assess other biodiversity WCS).

Table 2. Ape population estimates reported for Greater Mahale Ecosystem

Species	Year	Occurrence	Encounter or vistation rate (nests/km; ind/day)	Density estimate [ind./ km²] (95% CI)	Abundance estimate (95% CI)	Survey area	Sampling method	Analytical framework	Source	Comments	A.P.E.S. database ID
Pan troglodytes schweinfurthii	2005				2600.0	Greater Mahale Ecosystem	Survey data		Plumptre et al. 2010
Pan troglodytes schweinfurthii	2010-2020	Present		0.86		Greater Mahale Ecosystem	Line transects		Carvalho et al. 2022	The study was carried out using data from nest surveys conducted between 2010 and 2020, except 2016 when no surveys were conducted, using line-transect distance sampling; generalized additive models (GAMs). Inaddition, the density estimates were reported as varying spatially and temporally (numerical values provided per stratum in article tables).

Sampling methods Analytical frameworks

Threats

In Tanzania, 90% of the country’s chimpanzees are found in the Greater Mahale Ecosystem, where suitable habitat is being lost and fragmented by the expansion of human settlements, conversion of land for agriculture, logging, and cattle herding (Chitayat et al. 2021). Chimpanzees in savanna-woodland mosaics, such as in the Greater Mahale Ecosystem, already live at relatively low densities, highlighting the need to identify and protect areas critical for chimpanzee conservation (Chitayat et al. 2021).

Table 3. Threats to apes reported for Greater Mahale Ecosystem

Category	Specific threats	Threat level	Description	Year of threat
1 Residential & commercial development	1.1 Residential areas	Present (unknown severity)	People settling in the area tend to locate near water sources. As a result, small riverine strips of forest, critical for chimpanzees and the endemic Kungwe apalis, are disappearing (WCS n.d.). Expansion of settlements and land use influencing chimpanzee density (Carvalho et al. 2022)	2018-Ongoing (2022)
2 Agriculture & aquaculture	2.1 Annual & perennial non-timber crops	High (more than 70% of population affected)	Conversion of chimpanzee habitat into agricultural land (GMERC n.d., Carvalho et al. 2022).	2018-Ongoing (2022)
2 Agriculture & aquaculture	2.3 Livestock farming & ranching	High (more than 70% of population affected)	Cattle herding (Chitayat et al. 2021, Carvalho et al. 2022).	2018-Ongoing (2022)
5 Biological resource use	5.1 Hunting & collecting terrestrial animals	Present (unknown severity)	Injuries caused by snares (GMERC).	Ongoing (2021)
5 Biological resource use	5.3 Logging & wood harvesting	High (more than 70% of population affected)	Clearing the forest for charcoal production (GMERC). Conversion of woodland and forest due to human activities (Carvalho et al. 2022).	2018-Ongoing (2022)
7 Natural system modifications	7.1 Fire & fire suppression	High (more than 70% of population affected)	Fires ignited by humans, contributing to habitat loss (WCS n.d., GMERC n.d.).	Ongoing (2021)
5 Biological resource use	5.1.2 Unintentional effects (species is not the target)	Present (unknown severity)	Great apes getting injured by traps likely intended for other animals (Naiman M. pers. comm. 2025).	Ongoing (2025)
5 Biological resource use	5.1.5 Persecution/human wildlife conflict	Present (unknown severity)	Humans and great apes often share natural spaces drawing water from the same sources, foraging the same wild resources like forest fruits, and occasionally crossing paths on trails all of which can lead to increased interaction and potential health or conservation challenges and conflict (Naiman M. pers. comm. 2025).	Ongoing (2025)
8 Invasive & other problematic species, genes & diseases	8.4 Pathogens	Present (unknown severity)	The potential risk of diseases trasmission between people and apes, or apes and people is reported (Naiman M. pers. comm. 2025).	Ongoing (2025)

Threats

Conservation activities

Government-led patrols are conducted in partnership with the Jane Goodall Institute to fight illegal activities, such as poaching and herding (GMERC n.d.).

Table 4. Conservation activities reported for Greater Mahale Ecosystem

Category	Specific activity	Description	Implementing organization(s)	Year of activity
2 Counter-wildlife crime	2.3 Conduct regular anti-poaching patrols	GMERC organise and sponsor patrols to combat illegal activities since 2009.		2009-Ongoing (2021)
4 Education & awareness	4.1 Educate local communities about apes and sustainable use	Educational activities about great apes are being conducted (Naiman M. pers. comm. 2025).		Ongoing (2025)
4 Education & awareness	4.2 Involve local community in ape research and conservation management	Community-led conservation projects and land-use planning (Jane Goodall Institute, since 1994) (Pintea & Bean, 2022). Local communities are involved in conservation programs through the provision of conservation extension services, participation in Village Natural Resources Committees, and the recruitment and training of village forest scouts to support patrols and manage great ape habitats and their ecological connectivity within their respective areas (Naiman M. pers. comm. 2025).	Jane Goodall Institute	1994-Ongoing (2025)
5 Protection & restoration	5.6 Habitat restoration	Forest rehabilitation and protection activities are reported (Naiman pers. comm. 2025).		Ongoing (2025)
7 Economic & other incentives	7.1 Provide monetary benefits to local communities for sustainably managing their forest and its wildlife (e.g., REDD, alternative income, employment)	REDD+ initiatives REDD+ carbon projects by Carbon Tanzania, Ntakata Forest (Carvalho et al. 2022). Local people are employed to work in conservation projects (Naiman M. pers. comm. 2025).		Ongoing (2025)
7 Economic & other incentives	7.2 Provide non-monetary benefits to local communities for sustainably managing their forest and its wildlife (e.g., better education, infrastructure development)	Providing fuel efficient ovens GMERC.		Ongoing (2021)
8 Permanent presence	8.1 Run research project and ensure permanent human presence at site	Research is regularly conducted at the site GMERC.		Ongoing (2021)

Conservation activities

Challenges

Table 5. Challenges reported for Greater Mahale Ecosystem

Challenges	Specific challenges	Source	Year(s)
2 Resources and capacity	2.3 General lack of funding	Naiman M. pers. comm. 2025	Ongoing (2025)
2 Resources and capacity	2.4 Lack of continuous/long-term funding	Naiman M. pers. comm. 2025	Ongoing (2025)
2 Resources and capacity	2.2 Lack of staff	Naiman M. pers. comm. 2025	Ongoing (2025)
4 Institutional support	4.3 Lack of protected area status	Carvalho et al. 2022	Ongoing (2022)

Challenges

Enablers

Table 6. Enablers reported for Greater Mahale Ecosystem

Enablers	Specific enablers	Source	Year(s)
2 Resources and capacity	2.5 Sufficient capacity/expertise to advise, design, or implement actions	Naiman M. pers. comm. 2025	2025
2 Resources and capacity	2.6 External partnerships that add expertise or resources	Naiman M. pers. comm. 2025	2025
1 Site management
3 Engaged community
4 Institutional support
5 Ecological context
6 Safety and stability

Enablers

Research activities

The Greater Mahale Ecosystem Research and Conservation group cover several topics in their research, such as chimpanzee behavioral ecology, bioacoustics, environmental and biodiversity monitoring, as well as research on yellow baboons and red-tailed monkeys (GMERC n.d.).

Documented behaviours

Table 7. Behaviours documented for Greater Mahale Ecosystem

Category	Behavior	Observation type	Prevalence	Observation dates	Source	Habituation	Species	Comment
	Not reported

Behaviours

Exposure to climate change impacts

As part of a study on the exposure of African great ape sites to climate change impacts, Kiribou et al. subm. extracted climate data and data on projected extreme climate impact events for the site. Climatological characteristics were derived from observation-based climate data provided by the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP, www.isimip.org). Parameters were calculated as the average across each 30-year period. For 1981-2010, the EWEMBI dataset from ISIMIP2a was used. For the two future periods (2021-2050 and 2071-2099) ISIMIP2b climate data based on four CMIP5 global climate models were used. For future projections, two Representative Concentration Pathways (RCP) were used. RCP 2.6 is a scenario with strong mitigation measures in which global temperatures would likely rise below 2C. RCP 6.0 is a scenario with medium emissions in which global temperatures would likely rise up to 3C by 2100. For the number of days with heavy precipitation events, the 98th percentile of all precipitation days (>1mm/d) was calculated for the 1979-2013 reference period as a threshold for a heavy precipitation event. Then, for each year, the number of days above that threshold was derived. The figures on temperature and precipitation anomaly show the deviation from the mean temperature and mean precipitation for the 1979-2013 reference period.

The estimated exposure to future extreme climate impact events (crop failure, drought, river flood, wildfire, tropical cyclone, and heatwave) is based on a published dataset by Lange et al. 2020 derived from ISIMIP2b data. The same global climate models and RCPs as described above were used. Within each 30-year period, the number of years with an extreme event and the average proportion of the site affected were calculated (see Kiribou et al. subm. for details).

Table 8. Estimated past and projected climatological characteristics in Greater Mahale Ecosystem

Value	1981-2010	2021-2050, RCP 2.6	2021-2050, RCP 6.0	2071-2099, RCP 2.6	2071-2099, RCP 6.0
Mean temperature [C]	22.8	23.9	23.9	24	25.5
Annual precipitation [mm]	1049	1026	1088	1027	1080
Max no. consecutive dry days (per year)	104.9	121.8	112.1	122.2	123
No. days with heavy precipitation (per year)	4.5	2.7	3.7	2.9	4.7

Table 9. Projected exposure of apes to extreme climate impact events in Greater Mahale Ecosystem

Type	No. of years with event (2021-2050, RCP 2.6)	% of site exposed (2021-2050, RCP 2.6)	No. of years with event (2021-2050, RCP 6.0)	% of site exposed (2021-2050, RCP 6.0)	No. of years with event (2070-2099, RCP 2.6)	% of site exposed (2070-2099, RCP 2.6)	No. of years with event (2070-2099, RCP 6.0)	% of site exposed (2070-2099, RCP 6.0)
Crop failure	2.5	0.01	1	0	2.5	0	3.5	0
Drought	0	0	0.25	25	0	0	0	0
Heatwave	0	0	0	0	0	0	0	0
River flood	1.5	13.66	2	17.73	1.5	13.38	3	9.58
Tropical cyclone	0	0	0	0	0	0	0	0
Wildfire	30	2.28	30	2.31	29	2.33	29	2.73

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  Precipitation anomaly in Greater Mahale Ecosystem

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  Temperature anomaly in Greater Mahale Ecosystem

External links

Greater Mahale Ecosystem Research and Conservation

Greater Mahale Ecosystem WCS

Greater Mahale Ecosystem Frankfurt Zoological Society

References

Carvalho, J. S., Stewart, F. A., Marques, T. A., Bonnin, N., Pintea, L., Chitayat, A., Ingram, R., Moore, R. J., & Piel, A. K. (2022). Spatio‑temporal changes in chimpanzee density and abundance in the Greater Mahale Ecosystem, Tanzania. Ecological Applications, 32(8), e2715. https://doi.org/10.1002/eap.2715
Chitayat AB, Wich SA, Lewis M, Stewart FA, Piel AK (2021) Ecological correlates of chimpanzee (Pan troglodytes schweinfurthii) density in Mahale Mountains National Park, Tanzania. PLoS ONE 16(2): e0246628. https://doi.org/10.1371/journal.pone.0246628

GMERC (n.d.). Conservation. https://www.gmerc.org/conservation

intea, L., and A. Bean. 2022. Local Voices, Local Choices: The Tacare Approach to Community-Led Conservation. Redlands, CA: The Jane Goodall Institute, Esri Press.
Plumptre AJ, Rose R, Nangendo G, Williamson E a., Didier K, Hart J, et al. Eastern Chimpanzee (Pan troglodytes schweinfurthii) Status Survey and Conservation Action Plan 2010–2020. Gland, Switzerland; 2010.

WCS. (n.d.). Greater Mahale Ecosystem. https://albertinerift.wcs.org/Wild-Places/Greater-Mahale-Ecosystem.aspx

Page created by: APES Atlas Team Date: 2021-10-14

Page updated by: Naiman Martin Mollel, Aime Mizero Date: 2025-09-08