Population Status and Some Ecological Aspects of Soemmerring's Gazelle (Gazella Soemmeri11g1) in Aw Ash National Park and Alledeghi Wildlife Reserve, Ethiopia
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Date
2001-06
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Addis Ababa University
Abstract
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 AfiĀ·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
tluĀ·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.
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Biology