Gorilla gorilla ssp. gorilla
|Scientific Name:||Gorilla gorilla ssp. gorilla (Savage, 1847)|
See Gorilla gorilla
|Taxonomic Source(s):||Mittermeier, R.A., Rylands, A.B. and Wilson D.E. 2013. Handbook of the Mammals of the World: Volume 3 Primates. Lynx Edicions, Barcelona.|
The Western Lowland Gorilla (Gorilla gorilla gorilla) is one of two recognised subspecies of Western Gorilla (Gorilla gorilla) (Groves 2001). Genetic data suggest that Cross River Gorillas (Gorilla gorilla diehli) diverged from Western Gorillas approximately 18,000 years ago (Thalmann et al. 2011). Western Lowland Gorillas are genetically separated into subpopulations by major rivers (Anthony et al. 2007, Fünfstück et al. 2014).
|Red List Category & Criteria:||Critically Endangered A4bcde ver 3.1|
|Assessor(s):||Maisels, F., Strindberg, S., Breuer, T., Greer, D., Jeffery, K. & Stokes, E.|
|Reviewer(s):||Williamson, E.A. & Mittermeier, R.A.|
|Contributor(s):||Baillie, J., Butynski, T.M., Gatti, S., Tutin, C. & Walsh, P.D.|
Western Lowland Gorillas have a large geographic range, covering almost 700,000 km². Between 1983 and 2000, the country of Gabon lost half its Gorilla population (Walsh et al. 2003). A recent evaluation estimated population declines using a predictive model that incorporated survey data collected across the range of the taxon between 2003 and 2013. The results show an 18.75% decline between 2005 and 2013, corresponding to an annual loss of ~2.56% (Strindberg et al. in prep). These population decreases were driven by a combination of poaching and disease. The current size of the population is being evaluated, but thought to be in the order of a few hundred thousand.
Despite their abundance and wide geographic range, in 2008 Western Lowland Gorillas were listed as Critically Endangered under criterion A: a population reduction of more than 80% over three generations (one generation is ~22 years). This listing was based on population losses due to poaching, disease and habitat loss. Illegal hunting has not ceased despite intense anti-poaching efforts and the threat of Ebolavirus has not been removed: poaching is intensifying with the expansion of access routes into forests and Zaire ebolavirus is still present in the forests of the region. In addition, habitat loss due to industrial agriculture is increasing, and the effects of climate change will become more evident. At a conservative rate of reduction (2.56% per year rather than 4%, calculated from Walsh et al. 2003), the reduction in the Western Lowland Gorilla population is predicted to exceed 80% over three generations (i.e., 66 years, 2005–2071). Gorilla gorilla gorilla thus qualifies as Critically Endangered.
|Previously published Red List assessments:|
The total range of Gorilla gorilla gorilla covers close to 700,000 km². The northwestern limit of their distribution is the Sanaga River in Cameroon; the northern limit is the forest-savannah boundary to a maximum of roughly 5°N; the eastern limit is the Ubangi River; and the Congo River south of its confluence with the Ubangi forms the southeastern and southern limits. Most Western Lowland Gorillas are found below 500 m asl, but some reach elevations of 600–800 m asl in the mountains of Gabon.
Native:Angola (Cabinda); Cameroon; Central African Republic; Congo; Equatorial Guinea (Equatorial Guinea (mainland)); Gabon
|Range Map:||Click here to open the map viewer and explore range.|
Western Lowland Gorillas are found in almost all of the protected areas in their geographic range and many of the logging concessions; the majority (78%) live outside the protected area network (Strindberg et al. in prep). They can reach high densities (3–5 individuals/km²) over large areas of both swamp and terra firma forests (Blake et al. 1995, Rainey et al. 2010) and can persist at high densities in well-managed logging concessions (Morgan et al. 2013). Gorilla population estimates are made using a standard index of abundance: night nest abundance and distribution, sometimes combined with predictive modelling. Extensive surveys carried out since the mid-2000s have suggested that 150,000–250,000 Gorillas occur in the areas surveyed (Williamson et al. 2013, Sop et al. 2015), but the total population size is currently being re-evaluated. Based on surveys carried out between 2003 and 2013, most Western Lowland Gorillas are now known to reside in the Republic of Congo (60%), followed by Gabon (around 27%) and southwestern Cameroon (10%) (Strindberg et al. in prep).
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Western Lowland Gorillas inhabit both swamp and terra firma lowland forests throughout Western Equatorial Africa, occupying a variety of forest types, including open- and closed-canopy moist mature, seasonally-inundated, and disturbed and secondary (regenerating) forest (Williamson and Butynski 2013). They occur at high density in vast swamps in northern Republic of the Congo. They eat fruit, seeds, leaves, stems, bark, shoots, roots, petioles, bracts, vine tendrils, invertebrates and earth (ibid.) Staple and fallback foods are pith and shoots of the families Marantaceae and Zingiberaceae, whereas fruit consumption varies greatly between seasons according to availability (Rogers et al. 2004). Some populations feed on Gilbertiodendron dewevrei seeds during mast fruiting (Blake and Fay 1997). Gorilla g. gorilla is sympatric with Pan troglodytes troglodytes throughout its range, and the two species show a high degree of dietary overlap. Annual home range may be as large as 25 km², but is more usually 10–15 km² and the ranges of neighbouring groups’ overlap extensively (Cipolletta 2004). Western Lowland Gorillas live in relatively stable groups composed of 10 individuals, on average, with one “silverback” adult male, several adult females and their offspring (Parnell et al. 2002).|
Western Gorilla reproductive rates are lower than those of Eastern Gorillas due to a later age of parturition and longer interbirth intervals between surviving offspring (Breuer et al. 2009). Life history data are available from a few habituated Western Lowland Gorilla groups and 20 years of observations in the Republic of Congo, and demonstrate a slower life history than Mountain Gorillas (Breuer et al. 2009). Males reach full maturity at 18 years and age at first reproduction of females is around 11 years (ibid.). Inter-birth interval averages 5.2 years for surviving births with offspring being weaned at four years of age (Stoinski et al. 2013). Generation time is estimated to be 22 years (see Appendix I in the supplementary material).
|Continuing decline in area, extent and/or quality of habitat:||Yes|
|Generation Length (years):||22|
|Movement patterns:||Not a Migrant|
|Use and Trade:||
Gorillas are completely protected by national and international laws in all countries of their range, and it is, therefore, illegal to kill, capture or trade in live Gorillas or their body parts.
The major threats to Western Lowland Gorillas are:
Gorilla gorilla is listed under Class A in the African Convention on the Conservation of Nature and Natural Resources and is on CITES Appendix I. All Gorillas are protected by national and international laws throughout their geographic range, but law enforcement is generally weak. Only 22% of Western Lowland Gorillas live in the protected areas that cover 14% of their geographic range, with a further 21% of of the population in FSC-certified logging concessions, which add up to 8% of their range (Strindberg et al. in prep). Although forest guards work in most protected areas and in the well-managed logging concessions, 58% of Western Lowland Gorillas and 78% of their range are unprotected and highly vulnerable to poachers.
Two targeted conservation action plans for the great apes of Western Equatorial Africa have been produced (Tutin et al. 2005, IUCN 2014). The areas where most of the world's Western Lowland Gorillas occur in geographically distinct blocks have been identified, and a series of actions outlined for each, which can be broadly encapsulated as:
|Errata reason:||This is an errata version of the 2016 assessment to correct some typos (e.g., to correct "Ebola virus" to "Ebolavirus") and some minor grammatical errors in the Justification, Population, Habitat & Ecology, Threats, and Conservation Actions sections, and to add one missing reference to the Bibliography section.|
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|Citation:||Maisels, F., Strindberg, S., Breuer, T., Greer, D., Jeffery, K. & Stokes, E. 2016. Gorilla gorilla ssp. gorilla (errata version published in 2016). The IUCN Red List of Threatened Species 2016: e.T9406A102328866.Downloaded on 23 January 2018.|
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