Examining the Spatial Structure of Woody Cover Within a Highway Road Effect Zone for Ocelots in Texas

Abstract

Assessment of locations where wildlife species cross highways is a key question in mitigating future wildlife-vehicle mortality. Examination of the spatial structure, complexities, and patterns of vegetation or other land-use types (i.e., cropland, urban areas) near roadways allows scientists to identify any thresholds that influence where animals are likely to die or successfully cross the roadway. We used a historic 1982 to 2017 dataset of ocelot (Leopardus pardalis pardalis) mortality locations and approximate road crossing locations of telemetered ocelots in the Lower Rio Grande Valley in Texas to examine the spatial structure of woody vegetation within a hypothesized road effect zone. We determined if there were differences in the spatial structure of woody cover within a 1050 m buffer of each successful crossing and roadkill location using PERMANOVA and principal component analyses. We used a similarity percentages analysis to determine the relative contribution of each aspect of spatial structure on differences in successful crossing and roadkill locations. We found statistically significant differences in spatial attributes of patches at the locations of successful crossing versus roadkill locations of ocelots at the 150 m spatial extent (pseudo-F1,41 = 4.85, P(perm) = 0.008, permutations = 9949). Largest patch index contributed most to the differences between successful crossing and roadkill locations (15.94%), followed by mean patch area (15.44%), percent woody cover (15.18%), aggregation indices (14.53%), Euclidean nearest neighbor (13.47%), edge (13.08%) and patch densities (12.36%). Roadkill locations were clustered in locations with lower-quality woody cover within 300 m of the highway. This suggests areas immediately surrounding roads need to contain woody patches that are larger and closer together to reduce the barrier-effects of roads. Such information is important for informing highway planners about where to encourage crossings or to build wildlife crossing structures to promote movement across the highway.