Spatiotemporal Effects of Free-Roaming Horses on White-Tailed Deer Distribution in Northwestern Costa Rica

The study of interspecific interactions helps scientists and conservationists understand the ability of species to coexist in a given area, improving the conservation and management of ecological communities. Here we present a case study where we tested whether spatial and temporal interactions of whitetailed deer (Odocoileus virginianus), an ungulate native to Costa Rica, and horses (Equus caballus), a domestic ungulate reintroduced to a protected area, might result in avoidance. We used a paired field design with 40 camera traps deployed in two adjacent 228-ha fields within northwestern dry forest of Costa Rica during the wet season. We used general linear models to evaluate the effect of horse presence and vegetation type on white-tailed deer spatial distribution, as well as the Pianka's index to assess evidence of spatial overlapping. In addition, temporal overlap between horses and deer was assessed using the overlap coefficient, and the temporal response of white-tailed deer to horse presence was assessed using a spatially explicit null model approach. Evidence indicated that white-tailed deer used sites with horses more than sites without horses and used grass and shrubland sites more than forested sites. Within the area with horses, spatial overlap between horses and white-tailed deer was intermediate, suggesting insights of a moderate degree of spatial partitioning. Horses and white-tailed deer both showed similar activity patterns with a high degree of overlap, but our null model approach suggested neutral interaction; thus, our results indicated non-negative effects of horse presence on white-tailed deer spatiotemporal activity. Our results are limited by spatial and temporal replication, so caution is recommended when using this information to make decisions in other sites where horses and deer coexist. However, this effort provides relevant and novel information for our study area and can help decision makers to better manage ecological communities in the northwestern dry forest of Costa Rica. (c) 2022 The Society for Range Management. Published by Elsevier Inc. All rights reserved.