Effect of predation on adult pronghorn Antilocapra americana (Antilocapridae) in New Mexico, Southwestern USA

Abstract

Abstract The effect of predation on ungulate populations remains contentious, despite a lack of evidence showing impacts in arid Southwestern USA populations where low precipitation and frequent drought limit ungulate nutritional condition. These conditions can increase predisposition of prey to mortality, which is prerequisite for predation to be compensatory. Consequently, we tested the effect of predation on adult pronghorn Antilocapra americana (Ord 1815) in two populations in arid New Mexico by modeling transformed annual survival rates as a function of predation rates. For this conservative test, a slope=0 indicates complete compensation, whereas a slope=−1 indicates complete additivity. The corrected slope of mortality potentially attributable to predation was >−0.14, and this result was consistent among individual populations. Thus, predation was primarily compensatory. Primarily compensatory predation was related to the relatively low condition of pronghorn individuals, as predated individuals were all below the mean condition of the population, similar to results seen in previous tests of the compensatory versus additive predation hypothesis in the arid Southwest USA. Conditions that predispose individual ungulates to mortality are present more often than not in arid environments, and thus managers should not assume that predation is limiting, regardless of predation rates.