In search of the optimal management strategy for Arabian oryx

Abstract

Extirpated from the wild in 1972 by overhunting, Arabian oryx (Oryx leucoryx) were re-introduced in Saudi Arabia in March 1990; 17 oryx were released into Mahazat as-Sayd, a 2244 km 2 fenced reserve in westcentral Arabia, which lies at the periphery of their historical home range. The population has increased to 346 animals. The National Commission for Wildlife Conservation and Development, and those that manage the herd, have recently asked, 'What is the optimal management strategy to assure long-term persistence of the species, given the absence of immigration and predation?' Food resources, determinants of rates of mortality and birth, covary with unpredictable rainfall in Mahazat as-Sayd. Using data-driven assumptions, we developed a computer model that evaluated the probability of extinction (P ex ) under various management strategies: no intervention, removing a fixed number of animals each year, removing a fixed percentage of animals each year, and removing all individuals above a threshold. In addition, we explored the probability that oryx populations would decline below two thresholds, called the probability of quasi-extinction (P q-ex ) under various management schemes. Our analyses suggested that, without intervention, the oryx population had a high P ex . Removing 15% of the current population provided a low P ex , but this method also produced high values for P q-ex and, as a by-product, wide fluctuations in population size (N). Although it required an assessment of both N and carrying capacity (K), the most successful management plan consisted of removing all oryx above 70% of K. Adoption of this plan resulted in low P ex, low P q-ex , and smaller fluctuations in N. Our study may provide a useful model for evaluating management plans for a variety of threatened animal populations in desert ecosystems.

Heterothermy and the water economy of free-living Arabian oryx (Oryx leucoryx)

“…In 1990, Arabian oryx were reintroduced into Mahazat as-Sayd, a large protected area 160·km north-east of Taif, Saudi Arabia. Captive-reared animals survived and reproduced without supplemental food and water; the population has increased significantly over the past decade and now numbers more than 450 individuals (Ostrowski et al, 1998;Treydte et al, 2001). Arabian oryx can live without access to drinking water in arid and hyperarid deserts , including the Rub al-Khali, one of the driest regions in the world (Meigs, 1953).…”

Do Harvest Refuges Buffer Kangaroos Against Evolutionary Responses to Selective Harvesting?

“…For example, sanctuaries for endangered species are occasionally so successful that managers are forced to control population density through translocations or culling (e.g., Sukumar 1991, Armbruster and Lande 1993, Chapman et al 1998, Treydte et al 2001. In this case, potential indirect genetic effects of ''harvesting'' cannot be ignored.…”

Optimal Conservation Effort for a Population in a Stochastic Environment

“…The optimal management of natural biological resources has been studied in various situations n (Haight, 1995;Mo¨lsa¨et al, 1999;Senina et al, 1999;Bulte & van Kooten, 2001;Treydte et al, 2001). For example, Milner-Gulland et al (2001) developed a computer simulation model for an animal population in a stochastic environment, and compared different harvesting strategies with respect to the achieved revenue and its variability.…”