Understanding an ecological tug of war: Disentangling competition between native and domesticated ungulates

Abstract

Competition is a complex ecological process involving individual and community interactions at ecological and evolutionary time scales. Individuals within and between species can compete through two mechanisms: exploitative and interference competition. These mechanisms often co‐occur, making it difficult to develop a mechanistic understanding of competition. We used movement data from 19 GPS‐collared white‐tailed deer (Odocoileus virginianus) associated with an experimental cattle (Bos taurus) stocking event to disentangle exploitative from interference competition between deer and cattle. We assumed any effect of exploitative competition on reduced forage availability for deer would not occur immediately, whereas interference competition would occur immediately after cattle stocking, and antagonistic interactions between deer and cattle would alter deer behavior and degrade habitat quality. We evaluated the effects of the experimental stocking event on deer for 30‐day intervals before and after the cattle stocking event as this period was assumed to be too short for cattle to reduce deer forage resources through exploitative competition. We assessed the effects of interference competition using the movement metrics of home range size, speed, and resource selection. We used home range size as a proxy for habitat quality, assuming cattle would degrade deer habitat through means other than loss of forage. We used speed and resource selection as indicators of deer behavior. We experimentally stocked cattle at densities ranging from 0 to 15.7 animal units/km2 to previously destocked pastures. Stocking densities did not influence home range sizes ( = 17.033, 85% CI: −189.471 to 235.322) of deer. However, as stocking density increased, deer decreased speed ( = −0.014, 85% CI: −0.020 to −0.008) and increased selection for woody cover ( = 0.047, 85% CI: 0.031 to 0.063) and sandier soils ( = 0.062, 85% CI: 0.033 to 0.090). Our results suggest cattle density altered deer behavior and their realized niche within our system. Our results demonstrated mechanisms by which competition with livestock could influence native wildlife populations, which can be used to inform management of multiuse working landscapes.