Comparability of three analytical techniques to assess joint space use

Abstract

The degree of space‐use overlap among adjacent individuals is a central focus of many wildlife investigations. We studied the comparability of minimum convex polygon and fixed‐kernel home‐range overlap indices and Volume of Intersection (VI) scores using simulated data. We simulated pairs of point patterns to represent telemetry locations of adjacent individuals and varied the amount of potential overlap in the simulation region (100%, 50%, and 10%) and the point distribution (random, loosely clumped, and tightly clumped). We created 1,000 pairs of point sets (60 points in each individual set) for each of the 9 potential overlap and point distribution combinations. In all 9 treatment combinations, VI scores were highest followed by kernel and then polygon estimates. Raw differences among estimates within a treatment were greatest when there was 50% potential overlap, and overlap indices decreased as the degree of clumping increased. The relative differences among overlap indices within a treatment were affected most by potential overlap; differences generally were greatest at 10% and least at 100%. Correlation between index values was lowest for random point patterns, and highest for loosely clumped and tightly clumped point patterns. Although the VI tended to indicate the most overlap and minimum convex polygon the least, there was no consistent correction factor among techniques because of the interacting effects of the overlap index, distribution pattern, and potential overlap. Interpretation of overlap measures requires careful consideration of assumptions and properties of animals under study.

Female breeding dispersal in wolverines, a solitary carnivore with high territorial fidelity

“…From the UD, a specific proportion (isopleth) of the animal's use of space can be retained; we used the 90% isopleth as the annual territory and the 50% isopleth as the core area . We quantified fidelity by estimating the overlap between annual UDs using the volume of intersection index (VI) for both the territory and core area levels (Millspaugh et al 2004). VI values range from 0 (no overlap) to 1 (identical UDs).…”

Are migrant and resident elk (Cervus elaphus) exposed to similar forage and predation risk on their sympatric winter range?

“…We described winter home ranges of elk with utilization distributions (UDs), which define the home range boundary (x-y plane) and intensity of use (z-axis) throughout the home range (Millspaugh et al 2004). We estimated monthly UDs for each GPS-collared elk based on 2-h relocations collected during the winters (15 October to 15 April) of 2001-2005 using fixed kernel analysis (Worton 1989) with the plug-in method to determine the smoothing factor.…”

“…To measure home-range overlap between pairs of elk, we used the volume of the intersection index (VI), which estimates the volume of overlap between two UDs (VI ranges from 0 to 1, with 0 indicating no overlap and 1 indicating complete overlap) (Seidel 1992). The use of UDs and VI to estimate home-range overlap is more descriptive than traditional measures (e.g., minimum convex polygon) because the intensity of use within overlapping portions of the home ranges is accounted for (Millspaugh et al 2004;Fieberg and Kochanny 2005).…”

Spatial and Temporal Analysis of Contact Rates in Female White‐Tailed Deer

“…The JUD describes the joint probability that 150 both members of a pair will be found in the same area, assuming independent movements. The 151 JUD thus indicates both the amount of space jointly used and how similarly the 2 animals use 152 space within that overlap zone (Millspaugh et al 2004 ground-truthing to identify and delineate landcover types . 163 We used compositional analysis (Aebischer and Robertson 1992, 1993) to test for 164 nonrandom distribution of direct contacts between a deer pair among landcover types.…”