Sympatry Increases Predation Risk for an Endangered Ungulate

ABSTRACT

Predation risk for depleted prey populations is known to be influenced by prey abundance. However, predation risk may also be influenced by the abundance of sympatric prey species, particularly when the sympatric species is abundant. This suggests that predation risk estimates for low‐abundance prey may also need to account for the abundance of sympatric species. To understand how sympatry between two prey species with differing abundances affects predation risk, we used an unstudied system in arid Southern California where the co‐occurrence of federally Endangered Peninsular bighorn sheep ( Ovis canadensis nelsoni ) and southern mule deer ( Odocoileus hemionus fuliginatus ) is thought to affect the predation risk bighorn experience from pumas ( Puma concolor ). We characterized predation risk for bighorn and deer across their ranges to understand how topography, habitat, forage, and prey habitat suitability affect where pumas are likely to kill both species. The presence of the second ungulate species increased predation risk for both species, but had the greatest effect on bighorn, with predation risk strongly increasing with deer habitat suitability. The importance of deer habitat suitability to bighorn predation risk confirmed how spatial overlap between low and high abundance prey species can lead to increased predation risk, particularly for lower density ungulate populations. Our results provide more accurate estimates of bighorn predation risk, which is critical to the success of ongoing population recovery, and demonstrate how the density of sympatric species can be considered in population models and management.