Exploring the Influence of Vertical Relief on Large Mammal Home Range and Occurrences of Illegal Activity
Date
2024-05
Authors
Pinon, Andrea E.
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Abstract
Home range analyses that do not incorporate topography may result in miscalculation of a species home range size. It is especially problematic where conservation of endangered species and habitat rely on robust and accurate estimations to determine areas of high priority. Mountain gorillas, African buffalo, and antelope that occupy Volcanoes National Park (VNP) within the greater Virunga Conservation Area (VCA) in Central Africa range across a geomorphically unique region shaped by intense volcanism and tectonic activity. The extent to which terrain influences the home range size of the endangered mountain gorilla and the co-occurrence of illegal activity with targeted buffalo and antelope populations remains largely unstudied. Estimates calculated using traditional planimetric methods are poor approximations because they are calculated using bivariate locational data (x,y) which assumes a flat terrain. Given the complexity of the region’s physical geography, relying on bivariate home range estimates grossly underestimates the actual spatial area occupied by an animal when landform structure is excluded from analysis. This research is exploratory in nature and focuses on incorporating topography to generate a topographic home range. Mountain gorillas move within multiple dimensions of a spatial unit. Adding a third dimension (z) to home range geospatial analyses accounts for their vertical movement along an elevational gradient. Home range models derived from multi-dimensional (x,y,z) inputs provide more robust size estimates while accurately representing the physical landscape species occupy. Furthermore, we can test how home range models perform under different digital elevation surface spatial resolutions to derive the most accurate estimates using the finest resolution possible. Improved home range estimates expose patterns of overlap between species and illegal activity (e.g., snare poaching, beehive extraction sites), informs conservation management and guides antipoaching patrols. This study intersects spatial ecology with geomorphometry and geospatial analysis techniques. Digital elevation models (DEM) of varying spatial resolutions and kernel density estimation (KDE) methodology were applied to derive home range estimates. Terrain surfaces were generated to determine which variable; elevation, slope, or aspect has the greatest impact on size estimates. These terrain parameters including terrain ruggedness index were used to determine patterns of spatial cooccurrence of illegal activity and targeted species populations. Results indicated that topographic home ranges were larger than planimetric estimations and that slope, not elevation, had the greatest impact on size increases. Fine resolution DEMs produced more accurate and larger topographic home range sizes compared to coarse resolution DEMs. Among all terrain parameters, elevation and slope had the greatest impact on the co-occurrence of unauthorized activity and targeted animals.
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Keywords
home range, mountain gorilla, topographic home range, African buffalo, bushbuck, duiker, planimetric, topography, fixed kernal density estimation
Citation
Piñon, A. E. (2024). Exploring the influence of vertical relief on large mammal home range and occurrences of illegal activity (Unpublished dissertation). Texas State University, San Marcos, Texas.