Full screen
Artiodactyla
Id code: amd220Bovidae
Tragelaphus buxtoni
(Lydekker, 1910)
(Eng) Mountain nyala
(Fre) Nyala de montagne
Taxonomic notes
No significant taxonomic notes.
IUCN threat category
Endangered (EN: criteria A1a, C1).
Available information
Literature available on the ecology of this rare species is very limited. Ecological notes, distribution, and conservation issues are reported in Yalden & Largen (1992) and Yalden (1988). General information on its ecology is found in Kingdon (1997), Stuart & Stuart (1997) and Haltenorth & Diller (1980). Status and distribution are discussed in East (1988); the author also gives some information on its ecology, particularly habitat requirements.
Known extent of occurrence
The mountain nyala is endemic to Ethiopia (East, 1996), being found only to the east of the Rift Valley (Wilson & Reeder, 1993). Its distribution map was acquired from the accurate country map in East (1988) and was revised by Dr. R. East (23 June ‘97), who underlined that the only certain refuge for this species is currently represented by the Bale Mts. Fig. 8.6.38.a shows the whole range as "certain" even if the nyala has been eliminated from most of it.
Categorical-discrete (CD) distribution model
The species is currently found in a mosaic of high altitude woodland, bush, moorland and associated grassland (Kingdon, 1997; East, 1988).
Based on these environmental preferences, the following scores were assigned (Fig. 8.6.38.b) (Tab. 8.6.38.a):
|
Score |
|
|
1 |
Drier woodlands, bushlands, shrublands and grasslands within montane and altimontane vegetation zones. |
|
2 |
Moist woodland and savanna mosaic within montane and altimontane vegetation zones . |
|
3 |
Croplands, forests and all vegetation types in lowland zones. |
|
suitable |
moderately suitable |
unsuitable |
Total |
||||
|
km2 |
% |
km2 |
% |
km2 |
% |
km2 |
% |
|
18 314 |
44 |
5 226 |
13 |
17 982 |
43 |
41 522 |
100 |
Tab 8.6.38.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 |
21 |
899 |
3 657 |
72.94 |
1.49 |
6.75 |
|
moderately suitable |
49 |
97 |
122 |
2.75 |
1.3 |
1.78 |
|
Total AO |
14 |
1 689 |
5 635 |
93.02 |
1.66 |
6.53 |
Tab 8.6.38.b: Area of Occupancy fragmentation indexes.
Probabilistic-continuous (PC) distribution model
The output of the probabilistic-continuous (PC) distribution model is shown in Fig. 8.6.38.c.
Validation
No occurrence of the species within the four sample areas.
Comments and conservation issues
The species is restricted to the high mountains of Ethiopia and the suitable range is significantly smaller than the total EO as drawn in Fig. 8.6.38.a. The total AO seems to be about 23 500 km2. Even though the number of patches seems to be high for the small AO, the LPI of the suitable areas indicates the availability of at least one larger patch that accounts for about 73% of the total AO. Actual fragmentation is probably much higher as the species’ presence is restricted to the higher mountain ranges. Much of the actual distribution is included in local protected area: about half of the total EO and the percentage increases to 65% if only the potential AO is included. Given the small AO, the small population size, and the difficulties in enforcing protection, even these high percentages may not be sufficient to ensure the conservation of the species.
|
SUITABILITY CLASS |
inside |
outside |
Total |
|
suitable |
29.48 |
14.63 |
44.11 |
|
moderately suitable |
7.48 |
5.11 |
12.59 |
|
unsuitable |
15.23 |
28.08 |
43.31 |
|
Total |
52.19 |
47.81 |
100 |
Tab 8.6.38.c: Percent of environmental suitability classes within EO (as obtained from the categorical-discrete distribution model) inside and outside the protected areas.
References
East R. (Ed.) (1988). Antelope Global Survey and Regional Action Plans. Part I: East and North East Africa. IUCN/SSC Antelope Specialist Group.
East R. (Ed.) (1996). Antelope survey update. IUCN/SSC Antelope Specialist Group: n° 2.
Haltenorth T., Diller H. (1980). A field guide to the mammals of Africa, including Madagascar. Collins, London.
Kingdon J. (1997). The Kingdon field guide to African Mammals. Academic Press, London and New York: Natural World.
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.
Yalden D.W. (1988). Small mammals of the Bale Mountains, Ethiopia. Afr. J. Ecol.: 26, 281-294.
Yalden D.W., Largen M.J. (1992). The endemic mammals of Ethiopia. Mammal Rev.: 22(3/4), 115-150.