The populations of the endemic gelada outside protected areas are less studied and population estimates are not available. As a result, a study was conducted to investigate population structure and distribution of geladas in Kotu forest and associated grasslands, in Northern Ethiopia. The study area was stratified into five habitats namely; grassland, wooded grassland, plantation forest, natural forest and bushland based on dominant vegetation type. Each habitat type was further divided into blocks and total counting technique was employed to count the individuals of geladas. The total mean number of gelada in the Kotu forest was 229 ± 6.11. The mean ratio of male to female was 1:1.178. Age composition of geladas comprised: 113 (49.34%) adults, 77 (33.62%) sub adults and 39 (17.03%) juveniles. The mean group size of gelada was 18± 2.0, out of which 2.5± 0.5 (13.89%) was all- male unit (AMU) and 15.5± 1.5 (86.11%) was one male unit (OMU) social system. The average band size was 45.0± 2.53. The highest number of geladas was recorded from grassland habitat 68 (29.87%) and the lowest from plantation forest habitat 34 (14.74%). Even though, the sex ratio was female biased, the proportion of juveniles to other age classes was very low, indicating negative consequences for the future viability of the gelada populations in the area. Geladas were widely distributed over open grassland habitat. For sustainable conservation of the geladas in the area there is a need for integrated management of the area with special attention on the conservation of the grassland habitat.
Key words: Age sturcutre, habitat, group size, band size, sex ratio
Introduction
Geladas are large primates with dark brown to buff coarse pelage with dark brown faces and lighter, pale eyelids (Ankel- Simons, 2007). Females have a shorter pelage than males (Puff & Nemomissa, 2005). Adult males are larger than adult females and marked sexual dimorphism is the characteristics of the species, with adult females around two-third the size of adult males. Adult females weigh on average around 11 kg, while adult males weigh 18.5 kg (Jolly, 1972). The unique, distinct characteristics of gelada are the hairless hourglass-shaped pink or red area of the skin located on the chest (Yalden and Largen, 1992).
There are two sub-species of geladas that occur in Ethiopia. These are:Theropithecus gelada gelada and Theropithecus gelada obscure. The former occur in the northern highlands and the latter occur in the centralhighlands of Ethiopia (Yalden, 1983; Gippoliti, 2010). The differences between in T.g. gelada and T.g. obscure are minimal; there are a few visible differences.Theropithecus gelada obscure has darker coloured dorsal fur and flesh coloured face (Belay and Shotake, 1998). This sub species inhabits the north-western area of the Great Rift Valley in Showa (Menz, Debrelebanos and Muger areas), and in the Wollo and Gojjam Provinces (Yalden, Largen, & Hilman, 1996); Moges, 2015; Abie and Bekele, 2017). However, Theropithecus gelada gelada (Gippoliti, 2010), has a lighter fur appearance. This subspecies inhabits the northern highlands particularly in Simen Mountains National Park (SMNP) and associated highlands (Yalden et al., 1996; Boehner, Bergman & McCann, 2008; Ejigu and Bekele, 2014) and few populations recently reported from in the highalnds of Tigray (Girmay and Dati, 2020). According to Mori and Belay (1990) and Moges (2019), there is also sub population of gelada distributed in the southeastern part of the rift valley in the Arsi province near to Bale Mountains National Park. Some pilot survey showed that the Arsi gelada populations can be regarded as yet another distinct subspecies, T. gelada arsi (Belay and Mori, 2006; Gippoliti, 2010; Shotake, Aijunth, Agatsuma & Kawamoton, 2016; Zinner et al., 2018). Arsi gelada population lives in a lower- elevation habitat ranging from 1,800 to 2, 300 m asl (Belay and Mori, 2006; Moges, 2019).Theropithecus gelada obscure located in Wolo province is the current study species.
According to Mori and Belay (1990), the distribution of gelada population on the Ethiopian plateau is associated with the availability of easily digested montane grasses. Geladas occur between an altitude of 1800 and 4400 m asl. The Blue Nile gorge and the upper Shebelle rift valley (east of the Bale massif) mark the western and southeastern borders and the range correspondingly (Gippoliti and Hunter, 2008). The highest population of gelada occurs in SMNP (Beehner et al., 2008; Asfaw and Subramanaian, 2013; Woldegeoriges, 2015). The second largest population of gelada is found in GCCA) (Moges, 2015). More recently, , populations of gelada are reported from Wof-Washa Forest (Gosh-Meda Area), central Ethiopia (Goshme and Yihune, 2018) and from eastern escapments of Tigray (Girmay and Dati, 2020). Gelada population is limited to the highly grassland cliff in the deep gorges in the central plateau, of the south wollo in Azwa and Arego patches of valley forest and associated grasslands ( Ayalew, 2009), north wollo specifically, in Mount Abune Yosef community conservation area (Eshete et al. , 2015), in Gondar area (Yalden et al., 1996), Borena Sayint National Park (Denknore forest) (Adem, 2009; Kifle, 2018) and population of gelada also occurs in the Wonchit valley in Amhara regional state between north shoa and south wollo (Kifle, Belay & Bekele, 2013). The southern isolated population of gelada is distributed over valley and forest escarpments of Robe, Amigna and Bele districts (woreda) in Arsi zone (Abu, 2011; Moges, 2019).
The population size of gelada in different parts of Ethiopia is surveyed with the help of direct counting method and population estimate is available for its well known ranges. According to Beehner et al.(2008), in the SMNP, the population size of gelada estimated to be about 4620 individuals. The GCCA population estimate is 1502 individuals of gelada (Moges, 2015). The population in and around Borena Sayint National Park (Kifle, 2018), Azwa and Arego forest patch (Ayalew, 2009), Wof-Washa forest (Gosh Meda area) (Goshme and Yihune, 2018), Debrelibanos highlands (Abie and Bekele, 2017) and Arsi (Robe, Amigna and Bele districts) (Moges, 2019) were estimated to be 2786, 914, 435,1608 and 1315 individuals respectively. A recenty survey in estern escarpments of Tigray estimated the poulation of gelada around Hawzien and Ganta-Afeshum to be 105 individuals (Girmay and Dati, 2020). According to the gelada population estimate above in its different ranges, the current gobal poulation estimate is about ten thousand individuals. However, Beehner et al. (2008), estimated the global population estimate of gelada over all its potential ranges from 50,000 to 60,000 individuals indicating wide gap in population estimate that imply poulations in most of its ranges remain unexplored.
Geladas that live in protected area received high conservation attention and have been studied very well at different time by different researchers (Hunter, 2001; Beehner et al., 2008 and WoldeGeorgis, 2015). However, populations of gelada have been known to face habitat degradation, fragmentation and loss throughout its range (Yihune, Bekele & Tefera, 2009; Andarge, 2010; Moges, 2015; Abi and Bekele, 2017). Particularly, populations of gelada that lived outside protected area receive little conservation attention (Kifle et al., 2013) and there is no sufficient study on such small fragmented forest habitat of the endemic primates that serve as population stock source with significant economical, ecological, social and cultural values. The gap between the total population estimate (50,000 to 60,000 individuals, Beehneret al. 2008) and the population clearly estimated so far is wide, indicating to explore all possible ranges of the species to come to sound global population estimate.
In the present study area (Kotu forest) anthropogenic activities such as livestock encroachments, logging and firewood collection are causing habitat degradation and fragmentation of the habitats of gelada in particular and wildlife in general (DelantaWoreda Agricultural and Natural Resource Development Office (DWANRDO), 2016). Furthermore, there is an active mineral (Opal) extraction activities going on in the area that degrades the habitat of the gelada. This mineral naturally occurs embedded within a rock in the cliffs (Rondeau et al., 2010), which are ideal habitat for gelada in providing cover against extreme temperatures, predator and serve as breeding sites. As a result, the active extraction of the mineral is severely reducing the cover requirement of the species. At the mean time , there is no exact population estimate of the geladas and information on population distribution of gelada among dominant habitat types.
In the field of population ecology accurate population estimates of wild animal populations are essential for a number of reasons. Primarily, population estimate across a time will help to determine whether the numbers of particular species in the given habitat are being maintained, in decline or in recovery (Beehner et al., 2008). Secondly, establishing accurate numbers for each species is a first step in conservation and to draft effective wildlife policy. Thirdly, it is also important to estimate the wildlife population and describe its distribution for managing human-wildlife conflict in and around protected areas and outside protected areas. Therefore, the present study is aimed at determining the population size and population distribution of geladas among dominant habitat types of Kotu Forest nexus for sustainable population conservation.
Methods