Browsing by Author "GebreMedhin, Berihun"

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    Population Status and Some Ecological Aspects of Soemmerring's Gazelle (Gazella Soemmeri11g1) in Aw Ash National Park and Alledeghi Wildlife Reserve, Ethiopia
    (Addis Ababa University, 2001-06) GebreMedhin, Berihun
    The distribution of Soemmerring's gazelle (Gazella soemmerillgi), which had a wide range in the East Ali"ica, is currently dwindling with the increasing human population density in the previous range. In Ethiopia, it had a wide range in the Eastern and Northeastem part 0 f the country. However, the population is declining, because of the loss of important habitats as a result of overgrazing, indiscriminate killing and other human factors. Field study on the population status and some ecological aspects of the species was conducted every month from January to December 2000 for eleven months in I1ala Sala (Awash National Park) and for nine months (April to December) at Alledeghi Wildlife Reserve. The result indicated that mean populations of 457.8 individuals were found in the selected study site in Alledeghi Wildlife Reserve, and 41.9 individuals were counted at IIala Sala - Awash National Park. Grouping pattem showed that cohesion was stronger. TelTitorial males detain females and other members of the group. The difference in mean group sizes of the gazelle between the two areas was significant. In comparing the two populations based on the main categories the difference was not significant (p=0.795). Mean group size for ANP was 4.4 while for A WR it was 16.8 individuals. A paired-sample t-test comparison of the total fi'equency of categories of the group sizes for the two areas showed a significant difference (p=0.026). Local variation in group size did exist in AWR (p=0.021). But this variable showed no significant difference (p= 0.414) in ANP. Herds of 6 - 10 were most common at Ilala Sala and 20 - 50 at AWR. However, herd size ranges Ii-om 3 - 250 individuals at A WR. Compating seasonal variations in group sizes showed no significant difference. The proPOliioni of time budgets apportioned to the five types of activities vatied among seasons and month~' Feeding activity comprises much of the time budgets of Soemmerring's gazelle ranging fr, m 39.8 to 50.7% during the dry season from 38.4 to 45.7% in the wet season in male an from 51.0 to 59.6% in dry season and from 59.8 to 64.6% in wet season in female. Df:.S:tribution of group sizes in grassland habitats of the two study sites showed a very high si ificant difference (p=O.OO). High proportion of groups of Soemmerring's gazelle was obsen ed in short-sized grass cover in Alledeghi Wildlife Reserve, where as in Awash National Ii frk most were observed in medium-sized grass cover. Open grassland habitat was the best p; rferred habitat to other. V111 ungulate evolves behavioral and morphological adaptations that optimize the tradeoffs between these problems. Thus, within the constraints of effective strategies against predator and successful mating, one would expect strong selective pressures towards efficient use of energy and nutrients for maintenance and reproduction. Ungulates show variation in ecological behavior in response to environmental stress through time and space. Some move to higher elevations in spring and summer in search of nutritious, new growing forage (Festa-Bianchet, 1988), while others migrate to exploit temporal differences in vegetation phenology (Berger, 1991). Forage quality, quantity and predator avoidance influence the migratory behavior of certain mammals (Festa-Bianchet, 1988). Habitat selection by an animal reflects a strategy that enhances survivorship and successful reproduction (Bowyer et ai., 1998). One solution offered to explain how animals deal with conflicting needs to forage efficiently and avoid predation is selection of habitats that minimize the ratio of predation risk to available forage (Pulliam and Danielson, 1991). Conversely, such animals would tend to avoid other habitats in which predation risk is higher and value of food lower. In areas where there is an inverse linear relation between risk of predation and forage, animals would be distributed mostly in the habitat with low predation and high forage. If, however, animals are displaced from this optimal habitat, because of inter-specific competition or dominance interactions with superior individuals, sub-optimal habitats could be selected until predation become too severe or forage too limiting for them to persist (FestaBianchet, 1988). Many of the life history characteristics of ungulates are shaped by risk of predation (Berger, 1991; Festa-Bianchet, 1988; Hilih, 1977), and predators are capable of regulating populations of ungulates under celiain conditions (Van Ballenberghe, 1987; Van Ordsol, 1984). Selection of habitat is likely to depend upon a dynamic set of conditions that include the 'state' of the individual, its environment, and perhaps its past and potential future state (Mangle and Clark, 1986 cited in Festa-Bianchet, 1988). Behavioral information is essential to the full understanding of the ecology of a species. Different animals show different behavioral responses to the ecological changes that occur in their habitats, seasonal changes of the year, and presence or absence of predators, etc. Vigilant behavior, as one of the behaviors observed in response to various changes in the environment, may help an animal to locate food source and avoid capture by predator (Bertram, 1980). Underwood (1982) investigated vigilance behavior in several African antelopes in relation to finding food as well as in avoiding predation. Large predators prefer tall grass for successful hunting. Van Ordsol (1984) noted that hunts by lions were more successful in tall grass than in short grass. On the other hand, prey species like reedbucks of the family Rudincinae prefer long grass to avoid predators (Irby, 1982; Roberts and Dunbar, 1991). Jamlan (1974) suggested that non-cryptic animals have tlll'ee major strategies available to avoid predation: (i) detecting the predator before it initiates the attack, (ii) outLUnning the predator during the attack, or (iii) attacking the predator. This study will examine, in part, the response of the Soel11l11ert'ing's gazelle to predation in different heights of grass cover. Seasonal movements in water-dependent large communities show a wet season dispersal and dry season concentration which can be related to the seasonality of rainfall and water availability, but those similar pattems do not prevail in the water-independent species (Durant et al., 1986). It is suggested that seasonal migration of herbivores in the grassland ecosystems of Eastern Afi'ica is correlated to the availability of green vegetation and hence in the proportion of important nutrients. Different species of animals make seasonal movements between habitats. In areas where food resources change with seasons, populations of mammals are known to move fi'om one type of habitat to another depending upon the season (Began et al., 1986). The availability of food resources affect the population dynamics and distribution of an animal species (Caughly and Sinclair, 1994). Knowledge of the relationship of an animal with its habitat is essential in understanding the ecological requirement of the species (Caughly, 1977). In addition knowledge in the feeding habits of an animal are essential for making and designing strategies for management. Many studies have dealt with the various ecological and behavioral aspects of the Wildlife in Afi·ica. Of the nearly dozens of gazelle species found in Africa, only few are well studied: Thomson's and Grant's gazelles are the most studied fi'om East Africa (Estes, 1967; Walther, 1977), while the dorcas (Gazella dorcas) and dama (Gazella dama) (Salah, 1987; Yoram Yom-tov, 1987; Grettenberg, 1986) gazelles fi'Om North Afi'ica and the Middle East have been studied to some extent. Excessive hunting by people, excessive grazing by domestic livestock, agricultural el(pansion, and other habitat modifications are identified as the main factors that adversely affected most population of the gazelle in the Middle East and Nm1h Africa (Salah, 1987). Little is known about the ecology and population status of SoenmlelTing's gazelle. Soemmerring's Gazelle (Gazella soemlllerillgi) belongs to the family EOl'idae, subfamily Antelopini. This Gazelle is large in size, with an elongated head and a relatively short neck (Dorest and Dandelot, 1970). It is adapted to bush and acacia scrub in hilly areas as well as open grassy plain (Kingdon, 1997). This gazelle generally inhabits thorn bush, open and grassy plain in hilly country and is considered to be both browser and grazer (Estes, 1991). It feeds on grass and herb, but may also browse on leaves of shrubs. Like other African wildlife species, Soemmerring's Gazelle is affected by the rapid growth of human population, which has an increasing demand of new land for agricultural expansion and grazing livestock (Hillman, 1988). In most of its habitats, Soennnerring's gazelle has suffered from decades of uncontrolled hunting with firearms and severe habitat degradation caused by man and domestic livestock, accentuated by recurrent droughts. These factors have reduced this formerly abundant gazelle to scattered, remnant populations and its 10ng-teJID survival is tlu·eatened. It occurs in few conservation areas such as Awash and Yangudi Rasa national parks, which have been considered as the important areas for the conservation of this gazelle. The status of Soemmell'ing's Gazelle is classified as "Vulnerable" in the IUCN's (International Union for the Conservation of Nature and Natural Resources) Red Data Book (IUCN 1990). The species is under high pressure of threat to extinction within its highly restricted distribution. The distribution of Soemmerring's Gazelle in Ethiopia was described as locally common in the N0l1heastell1, Eastell1 and Southeastell1 lowlands (Hillman, 1988). However, recent reports indicate that the species is exterminated over the greater part of their range, and occurs in numerous pockets (Kingdon, 1997). Schloeder et al. (1997) have repot1ed that large propot1ion of the population of the species in the Rift Valley of Ethiopia occurs in the Alledeghi Wildlife Reserve and the adjacent Afdem-Gewane Controlled Hunting Area. Thouless (1995) recorded 2,650 gazelles at the Alledeghi plains on the grassland plain to the West of the A wash River and North of the central part of the Awash West Controlled Hunting area. Soemmerring's Gazelle has also wide geographical range in Eastem Ethiopia. Their status was assessed in Aysha-Jijiga region by Thouless (1995) and in the Ogaden Region by Wilhemi (1997). These repot1s indicated that the population of the species is greatly on the decline. Although the status of Soemmerring's Gazelle is considered stable in the Awash Valley (Schloeder et al., 1997), its size in the Awash National Park (ANP), which is legally protected, has declined as compared to other antelopes (Almaz Tadesse, Personal Communication). The population has declined by over 82% in 27 years and its important habitat shrunk by a similar margin (Schloeder et al., 1997). Assessment of the current status and ecology of So emmer ring's gazelle is impot1ant for the park management and will also provide some information on the existing knowledge gap on ecology of this gazelle.