Influence of exotic horses on the use of water by communities of native wildlife in a semi-arid environment

Introduced species can impact native communities by altering competition dynamics. Large exotic species, such as the horse (Equus caballus), may have a competitive advantage over smaller native species and could exclude them from access to limited resources. Our objective was to determine the influence of the exotic horse on the use of water by native species in a semi-arid environment where availability of water is limited. From July 2010 to August 2011, we used remote cameras to monitor water sources in the Great Basin Desert where horses had drinking access and where horses were excluded (with fencing) to compare 1) composition of native communities and 2) water usage by native species. We captured 96,601 images representing 40 species of birds (29,396 images) and 13 species of mammals (67,205 images). Of the 67,205 images of mammals, 79% contained horses. Horses were associated with decreased richness and diversity of native species at water sources. Furthermore, native species had fewer visits and spent less time at water sources frequented by horses. Our results indicated that horses displaced other species at water sources providing evidence of a negative influence on how communities of native wildlife access a limited resource in an arid environment.