Assessing the role of woody cover in resource selection by sable antelope (Hippotragus niger) in northern Kruger National Park
Date
2010-02-17T11:42:57Z
Authors
Dabengwa, Abraham Nqabutho
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Abstract
The relationships between woody cover and habitat use by sable antelope (Hippotragus niger) in Kruger National Park (KNP) are poorly documented. Previous studies of sable antelope habitat did not explicitly measure space use and its relationship to habitats attributes. Global positioning system (GPS) telemetry permits the accurate collection of animal locations, which can be used to estimate home ranges and utilisation distributions (UDs). Resource utilisation functions (i.e., functions regressing probabilistic space use by animals such as UDs on landscape attributes) were used to analyse relationships between habitat use and woody cover with historical black and white aerial photographs. The dot-grid and object-based image analysis (OBIA) methods were used to estimate woody cover from digital aerial photographs and the results validated with field collected woody cover data. The dot-grid method was used to estimate woody cover by expressing canopy hits as a percentage of total dots using a regular lattice of evenly spaced dots overlaid on digital aerial photograph sections. The OBIA approach selected homogeneous groups of pixels (i.e., objects) and incorporated image aspects such as shape, size, texture, and brightness into the woody cover classification. The size of the objects depended on the scale selected for identifying single woody plants and the resolution of the aerial images. The two woody cover estimators (i.e., the dot-grid and object-based image segmentation) produced contrasting results. However, more confidence was placed in the use of the dot-grid method. The linear regression models revealed weak/ non-significant relationships between woody cover and space use by sable antelope. However, woody cover was more abundant in the wet season home range (36 ± 1%) when compared with the dry season home range (30 ± 1%) (t 0.05, 163 = 3.8, P < 0.001). Woody cover in the dry season non-core areas (31 ± 1%) was significantly more than that in the core areas (28 ± 1%) (t 0.05, 182 = -1.7, P = 0.04). The avoidance of home range areas with more woody cover during the dry season suggests that sable antelope are risk sensitive foragers that maximise the intake of available low quality food resources. The results from this study also indicate that sable antelope may be selecting for woody cover at scales larger than the one used here.