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Primates
Id code: amd057Loridae
Arctocebus calabarensis
(J. A. Smith, 1860)
(Eng) Calabar angwantibo
(Fre) Potto de Calabar
Taxonomic notes
It does not include A. aureus, recognised as a distinct species (Wilson & Reeder, 1993; Oates, 1996).
IUCN threat category
Lower Risk, near threatened (LR: nt).
Available information
Most of the studies on this species refer to A. c. aureus, only recently recognised as a fully separate species (Bourlière, 1985; Charles-Dominique, 1971, 1977, 1979; Eisenberg et al., 1979). General information on the species’ ecology is found in Estes (1991), Kingdon (1997), and Stuart & Stuart (1997). Status, threats, and distribution are analysed in Lee et al. (1988) and Oates (1996).
Known extent of occurrence
The angwantibo ranges in Cameroon and Nigeria, between the Niger and Sanaga Rivers (Wilson & Reeder, 1993). The distribution map was obtained from Charles-Dominique (1977) and revised using information found in Kingdon (1997) to match the river network (Fig. 2.1.2.a).
Categorical-discrete (CD) distribution model
This species prefers tree-fall zones and the lower forest layer in primary and secondary forest (Kingdon, 1997; Lee et al., 1988).
Based on these environmental preferences, the following scores were assigned (Fig. 2.1.2.b) (2.1.2.a):
|
Score |
|
|
1 |
Forests. |
|
2 |
Forest mosaics. |
|
3 |
Savannas and croplands. |
|
suitable |
moderately suitable |
unsuitable |
Total |
||||
|
km2 |
% |
km2 |
% |
km2 |
% |
km2 |
% |
|
77 132 |
43 |
70 240 |
39 |
33 771 |
19 |
181 143 |
100 |
Tab 2.1.2.a: Cumulative size (km2) of areas pertaining to each environmental suitability class within the Extent of Occurrence.
|
Number Patches (NP) |
Mean Patch Size (MPS) km2 |
Patch Size SD (PSSD) km2 |
Largest Patch Index (LPI) % |
Mean Shape Index (MSI) |
Area-Weighted Mean Shape Index (AWMSI) |
|
|
suitable |
122 |
630 |
4 980 |
37.05 |
1.35 |
9.25 |
|
moderately suitable |
166 |
429 |
2 610 |
16.44 |
1.35 |
7.67 |
|
Total AO |
9 |
16 456 |
46 428 |
99.78 |
2.19 |
10.68 |
Tab 2.1.2.b: Area of Occupancy fragmentation indexes.
Probabilistic-continuous (PC)distribution model
The output of the probabilistic-continuous (PC) distribution model is shown in Fig. 2.1.2.c.
Validation
|
% of EO in sample areas |
Number of valid plots |
Index of Accordance (%) |
|
51.80 |
41 |
53.66 |
Tab 2.1.2.c: Categorical-discrete (CD) distribution model validation parameters.
Comments and conservation issues
The Index of Accordance of 53.66% for the CD model shows a sufficient level of reliability especially considering that the sample areas for the field work cover more than 50% of the known EO. Within the known EO, the species lives primarily in forests and these account for only 43% of the total EO. Although forests are still widespread in eastern Nigeria and western Cameroon, they do not form a large uninterrupted block: the fragmentation indexes show that suitable areas and moderately suitable areas compenetrate each other thus forming an intricate mosaic (NP, MPS and LPI). The AWMSI of the total AO indicates that a mosaic with the unsuitable areas is also widespread. This is most obvious in the northern part of the range in Nigeria and western Cameroon. About 2.8% of the total AO is included in existing protected areas: although the species is classified as Lower Risk, this percentage is far too little to protect a species with such a small distribution range.
|
SUITABILITY CLASS |
inside |
outside |
Total |
|
suitable |
1.64 |
40.94 |
42.58 |
|
moderately suitable |
0.71 |
38.06 |
38.78 |
|
unsuitable |
0.88 |
17.76 |
18.64 |
|
Total |
3.23 |
96.77 |
100 |
Tab 2.1.2.d: Percent of environmental suitability classes within EO (as derived from the categorical-discrete distribution model) inside and outside the protected areas.
References
Bourlière F. (1985). Primate communities: their structure and role in tropical ecosystems. Int J. Primatol.: 6, 1-26.
Charles-Dominique P. (1971). Eco-éthologie des prosimiens du Gabon. Biol. Gabonica: 7, 121-228.
Charles-Dominique P. (1977). Ecology and Behaviour of Nocturnal Primates. Prosimians of Equatorial West Africa. Columbia University Press, New York.
Charles-Dominique P. (1979). Ecology and feeding behaviour of five sympatric lorisids in Gabon. In: Sussman R.W. (Ed.). Primate Ecology. Problem-oriented field studies. Wiley, Chichester & New York: chap. 1:1-22.
Eisenberg J.F., Muckenhirn N., Rudran R. (1979). The relations between ecology and social structure in primates. [reprinted from Science (1972), 176: 863-874]. In: Sussman R.W. (Ed.). Primate Ecology. Problem-oriented field studies. Wiley, Chichester & New York. chap. 23: 455-484.
Estes R.D. (1991). The Behaviour Guide to African Mammals. Including Hoofed Mammals, Carnivores, Primates. The University of California Press.
Kingdon J. (1997). The Kingdon field guide to African Mammals. Academic Press, London and New York: Natural World.
Lee P.C., Thornback J., Bennet E.L. (1988). Threatened Primates of Africa. IUCN, Gland - Switzerland and Cambridge, UK.
Oates J.F. (1996). African Primates Status Survey and Conservation Action plan. IUCN/SSC Primate Specialist Group.
Stuart C., Stuart T. (1997). Field guide to the larger mammals of Africa. Struik Publishers.
Wilson D.E., Reeder D.M. (Eds) (1993). Mammal Species of the World: A Taxonomic and Geographic Reference. Second edition. Smithsonian Institution Press, Washington D.C.