Exotic oryx interact with shrub encroachment in the Chihuahuan Desert

Abstract

Biotic invasions can interact with ongoing landscape transitions in introduced ranges, acting synergistically to accelerate landscape change. The African oryx (Oryx gazella), a large ungulate native to the Kalahari Desert in southern Africa, was intentionally released into the Chihuahuan Desert of southern New Mexico to provide increased hunting opportunities. Oryx have subsequently dispersed widely, including into the adjacent Jornada Basin Long Term Ecological Research site, which contains native grassland communities imperiled due to shrub encroachment. We examined how landscape use and diel activity of oryx interacts with shrub encroachment at Jornada Basin. We hypothesized that oryx would be more common on unencroached grasslands that provide preferred forage, and that oryx would be most active at dawn and dusk (crepuscular) when ambient temperatures were favorable and predator surveillance was possible. We sampled 24 sites across a broad gradient of shrub encroachment from 2014 to 2018 using camera traps to evaluate our hypotheses. Oryx relative abundances were higher on unencroached grasslands, especially in years of low to moderate precipitation. We found oryx were most active during crepuscular periods, and this behavior was consistent across the shrub encroachment gradient. Our research suggests exotic oryx could contribute to shrub encroachment by focusing their foraging on remaining grasslands, especially during drier years, which may adversely affect livestock production and other ecosystem services.