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Abstract

Introductions of exotic species can benefit certain publics but can also have many unanticipated consequences. South African oryx (Oryx gazella gazella) were introduced into the Chihuahuan Desert on White Sands Missile Range (WSMR), New Mexico, USA to alleviate a perceived lack of large mammal hunting opportunities. Because of conflicts with oryx as the population increased, we modeled population growth and determined survival of radio-collared oryx to identify rates of population increase, limiting factors to population growth, and levels of harvest necessary to control population growth. Following introductions in 1969–1977, oryx significantly increased their range and showed a rate of increase of approximately λ = 1.22 through 2000, reaching approximately 3,500 individuals. This rate was marginally positively influenced by total precipitation received the previous year and near the species maximum based on fecundity (approx. λ = 1.26–1.29). In response to concerns over conflicts with oryx on WSMR, intensive studies of oryx limiting factors, 2001–2003, found annual survival of oryx excluding recovered harvest was ≥0.95 for adults and 1.00 for subadults. Most of the mortality was unrecovered hunting loss, further indicating that oryx had few nonhuman limiting factors. Modeling of the oryx population indicated that adult female harvest must be approximately 0.22–0.25 to control population growth. Intensive harvesting aimed at controlling oryx numbers removed an average of 30 (SE = 2.0)% of the estimated population, 2001–2013, which decreased the population to approximately 1,700 by 2013. Decreased harvest intensity from 2014–2017 to approximately 16 (SE = 1.6)% of the population subsequently allowed oryx to increase again at approximately λ = 1.14, rebounding to around 2,900 by 2017. Introduction of oryx succeeded in increasing recreational opportunities and revenue for management agencies. However, negative impacts on military missions, vehicle–oryx collisions, possible disease impacts on native ungulates, impacts on protected areas, the logistics of managing hunting programs on a closed military reservation, and optimizing oryx-related revenues continue to be significant management challenges.

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