Kingdom of Saudi Arabia. Towards the effective management of the Arabian oryx Oryx leucoryx in the Kingdom of Saudi Arabia. By W. M. STRAUSS, Pretoria.
Z. Jagdwiss. 48 (2002), Supplement, 7-16 ]SSN 0044-2887 National Commission for tffldlife Conservation and Development (NCWCD). Kingdom of Saudi Arabia
Towards the effective m a n a g e m e n t of the Arabian oryx leucoryx in the Kingdom of Saudi Arabia
Oryx
By W. M. STRAUSS,Pretoria
1 Introduction
In Saudi Arabia the historical distribution of the Arabian oryx was closely associated with the distribution of the acolian sands. During the 1930's thc remaining Arabian oryxes in Saudi Arabia occurred in two populations which are, approximately 1100 km apart. These are the Great Nafud in the north, and in the Rub' al Khali basin in the south (Figure 1). Historically, the ad-Dahna sand belt probably served as a migration route between the northern and southern Arabian oryx populations. The demise and the subsequent rescue of the Arabian oryx in the Arabian Peninsula has been well documented (GRIMWOOD,1962; STANLEY-PRIcE,1989) and the rescue operation has been a major success story in conservation (STANLEY-PRICE,1989; SPALTON, 1993).
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Figure 2: The trends in the population size, the survival probability and the heterozygosity of the three existing Arabian oryx populations and a proposed new population (dashed line) in the Kingdom of Saudi Arabia over a lO0-year period when managed in isolation.
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migrations rates on the survival probalityof different Arabian oryx populations in the Kingdom of Saudi Arabia, as modeled over a 100 year peiod. Migration takes place from the Mahazat as Sayd and National wildlife Research Centre populations into the 'Uruq Bani Ma'arid and al-Khunfah populations respectively.
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Metapopulation model Sensitivity analyses showed that an increasing migration rate into the 'Uruq Bani Ma'arid population would result in increasing survival probabilities (Figure 3). A migration rate of 1% into this population increases the population's survival probability to 95%, mainly due to the resultant positive exponential population growth rate (r = 0.0170 • 0.3035). This rate of migration is equivalent to a mean of 0.59 males and 0.91 females entering the 'Uruq Bani Ma'arid population per year during those years that the Mahazat as Sayd population reaches 90% of its ecological capacity. The 'Uruq Bani Ma'arid population is predicted to reach a maximum population growth rate of 4.9% at a migration rate of 7.5% from the Mahazat as Sayd population. Such a high migration rate from the Mahazat as Sayd population does, however, result in an unacceptable survival rate (P( ...... ~) = 0.926) for this population (Figure
13 3). The models also predict that the Mahazat population can sustain migration rates of up to 5% without negatively affecting the survival of this population. A migration rate of 2% into the al-Khunfah population resulted in a 100% survival probability of the latter population (not illustrated), whilst having no negative effect on the survival of the captive population. At a 7% migration rate the captive population will still maintain a positive population growth rate (r = 0.1086 • 0.083) and the probability of survival during the 100-year modeling period at a 7% migration rate will be 99% for the captive population. The effect of the different migration rates on the heterozygosity levels of the source and the recipient populations are modeled in Figure 4. The lowest migration rates have no predicted negative effects on the heterozygosity levels of the source populations. These levels of migration do however, increase the heterozygosity of the recipient populations (compare Figure 4 with Figure 2). The maximum migration rate of 7.5% from the Mahazat population resulted in relatively low levels of heterozygosity (0.932 • 0.043) in this population at the end of the modeling period.
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4 Discussion
The captive Arabian oryx population is secure due to the high levels of management at this facility, which results in higher productivity and higher survival rates of all age classes. Epidemiological catastrophes were not modeled due to the stringent veterinary-monitoring programme that is in place at this facility and the difficulty of estimating the probability of such a catastrophe occurring. Even though the Mahazat as Sayd population is subject to catastrophes and natural mortality rates, the management activities in the area is likely to have a positive effect on the population's persistence. An example is the lower multiplicative effect that catastrophes are likely to have on reproduction. Because supplementary food and water
14 results in the females being in better condition and they are more likely to conceive and breed successfully, even though drought conditions may exist. In Oman it has been shown that food quality and the subsequent physical condition of the females are important for successfully reproducing during any particular year (SPALTON, 1995). It is well known that the variability in rainfall increases as one moves south in the Kingdom of Saudi Arabia (MANDAVILLE, 1986). The variability in the rainfall and the subsequent fluctuation in food quantity and quality are reflected in the probability of survival of the 'Uruq Bani Ma'arid population. Because of this variable environment the Arabian oryx population in the Rub al Khali probably always had a relatively low density at the best of times. Additional factors such as the changing grazing patterns of the livestock of the now less-nomadic Bedouin, due to the accessibility of supplementary food and water, further limits the spread of the Arabian oryxes outside the core protected area. This in turn affects the long-term viability of this population in a way that has not yet been determined. The fact that the 'Uruq Bani Ma'arid Protected Area has been nominated as an IUCN World Heritage Site, the wild experience offered due to its remoteness, the relatively unscathed environment and the scenic beauty of the area preclude management actions such as artificial waterholes and supplementary feeding. The further fact that the area is unfenced and that the supplementary food and water would attract and possibly largely only favour livestock, also makes this option undesirable. An alternative management approach would be to manage the oryx populations in the Kingdom as a single metapopulation. Establishing another free-ranging Arabian oryx population in the al-Khunfah Protected Area would spread the risk that ti'ee-ranging populations face in the Kingdom, while also recreating the aboriginal north-south Arabian oryx populations. The al-Khunfah Protected Area contains a section of the an-Nafud desert (CHILD and GRAINGER, 1990) and has previously been identified as an oryx reintroduction site. The modeling results showed that the captive facility at the National Wildlife Research Centre could supply enough animals for reintroduction, without affecting the captive population negatively. The suggested fate of reintroduction enables the al-Khunfah population to bypass the slow establishment phase typical of a new population (BOTHMA, 1996). Instead the population quickly enters the exponential growth phase due to sufficient numbers of breeding age oryx males and females in the area. This is essential, as it has been shown that the size of the founder population is important in successfully establishing a new population (WOLF et al., 1996). This population would, however, also be relatively small. Consequently it would also be subjected to the threats that all small populations face, as is illustrated by the relatively low probability of surviving the 100-year modeling period. In addition, changing livestock grazing patterns in the north of the Kingdom are also important limiting factors of this population. The collective management of different small populations of a particular species, distributed in various reserves is by no means new and has been suggested for the management of the roan antelope Hippotragus equinus in Rwanda (BEUDELS, et al., 1992). A similar approach is also being followed with small lion Panthera leo populations in private reserves in South Africa, although this mainly deals with the exchange of genetic material through artificial insemination and other procedures. The "metapopulation through management" approach as proposed here is predicted to show increased population persistence and heterozygosity, even at low levels of migration, for those populations most prone to extinction compared to when they are managed in isolation. A modest level of connectedness has also been shown to increase the probability of persistence of wild dogs Lycaon pictus (VUCETICH and CREEL, 1999). There are several deficiencies to the model proposed here. These are based on the
15 assumptions made and on some conservation issues that still has to be addressed, such as security concerns in the al' Khunfah Protected Area. Nonetheless, the models indicate that the collective management of all the Arabian oryx populations in the Kingdom of Saudi Arabia is likely to be advantageous to the free-ranging populations, which are most at risk. Acknowledgements The National Commission for Wildlife Conservation and Development in the Kingdom of Saudi Arabia is thanked for the opportunity to conduct fieldwork in the 'Uruq Bani Ma'arid Protected Area, and for their support during this time. The Centre for Wildlife Management at the University of Pretoria is thanked for their continued support. Prof. J. du P. BOTHMA reviewed the manuscript and provided helpful suggestions.
Summary Traditionally the distribution of the Arabian oryx in the Kingdom of Saudi Arabia has been closely associated with that of the major sand deserts, notably the Great Nafud in the north and the Rub' al Khali in the south. Due to a successful captive breeding programme the Arabian oryx was reintroduced in the 'Uruq Bani Ma'arid Protected Area, on the western edge of the Rub' al K_hali during 1995, thereby re-establishing the southern population in the Kingdom of Saudi Arabia. Population viability analysis is used to demonstrate the re-establishment of the northern oryx population, the vulnerability of certain populations and to suggest a management approach that should enhance the survival of the free-living populations in the Kingdom of Saudi Arabia. Population models predict that the 'Uruq Bani Ma'arid population could be subject to extinction (Psurvival = 0.38) when modeled in isolation. Associated with this is a low heterozygosity. The proposed release strategy of oryxes into a northern protected area results in maximum population growth during the first 20-years and continued positive population growth during the 100-year modeling period. The latter free-living population is, however, also subject to extinction due to its relatively small size. By managing all of the Arabian oryx populations in the Kingdom of Saudi Arabia as a single metapopulation, survival of the free-living populations are enhanced, without negatively affecting the other populations. Keywords: Arabian oryx, reintroduction, management, Population Viability Analysis
Zusammenfassung Zur tffektiven Bewirtschafi der arabischen O~x (Or)'x leucor3'x) im KOnigreich Saudi Arabien
Yraditionell ist die Verbreitung der arabischen Oryx im K6nigreich Saudi Arabien eng verbunden mit der Vcrbreitung der groBen Wfistenfl/ichen, insbesondere der GroBen Nafud im Norden und dem Rub' al Khali im Sfiden. Auf Grund von einem erfolgreichen Zuchtprogramm yon gefangenen Tieren konnte die arabische Oryx 1995 wieder in das Schutzgebiet 'Uruq Banii Ma'arid auf der westlichen Seite vom Rub'al Khali eingesetzt werden. Somit wurde die stidlichste Population im KSnigreich von Saudi Arabien re-etabliert. Die Analyse der Lebensffihigkeit der Population dient zur Demonstration der folgenden Gegebenheiten und MaBnahmen: die Wiederherstellung der nSrdlichen Oryx Population, die Gef'fihrdung yon bestimmten Populationen und den Entwurf yon einer
16 Bewirtschaflungsmethodc um das I~'bcrleben der frcilebenden Populationen im K6nigreich von Saudi Arabien zu fiSrdern. Populationsmodelle sagen voraus, dass die "Uruq Bani Ma'arid Population aussterben k6nnte (P ..........' 0,38) ~enn das Modellverfahren auf der Basis einer isolierten Population durchgeffihrt wird. Damit verbunden ist eine niedrioe Heterozygotie. Die vorgeschlagene Freilassungsstrategie yon Oryx in einem n6rdlichen Schutzgebiet ergibt einen maximalen Populationszuwachs wS.hrend der ersten 20 Jahren und verzeichnet weiterhin einen positiven Populationszuwachs wfihrend der gesamten 100 jfihrigen Modellperiode. l)iese letztere fieilebenden Population ist wegen ihrer geringen GraBe jedoch auch vom Erlaschen bedroht. Wenn alle arabischen Oryx-Populationen im K6nigreich x on Saudi Arabien als eine einzige Gro6population bewirtschaftet werden, dana wird die t~berlebensrate der freilebenden Populationen gel~Srdert ohne die anderen Populationen negativ zu beeinflussen. Schlii,s,selwSrter: arabische Oryx, Wiedereinbfirgerung, t3ewirlschaflung, Analyse der I,ebensl,ihigkeit der Population
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