A Dynamic Test of Spatial Independence Among Bighorn Sheep

Abstract

The spatial interactions of marked study animals are often of interest in studies of wildlife ecology. All forms of resource selection analysis assume that marked individuals move and select resources independently, and this is often violated when animals are social or territorial. For this paper we deal with relocation data collected from a gregarious species, bighorn sheep (Oiis canadensis), and wish to assess the spatial independence of marked animals. Many commonly used methods for quantifying spatial interactions do not include the spatial and temporal details of simultaneous relocation data. In their place, we used a modified nearest-neighbor method and data from three small herds of bighorn sheep in western Montana to test for independence among marked animals. Results suggested that marked ewes within each study area were not selecting habitat independently of one another. Consideration of spatial independence can be important in a posteriori analysis and interpretation of data, as well a priori consideration of necessary sample sizes.