ETD Collection

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Subject: search.filters.subject.Gemsbok.

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    Movement ecology of gemsbok in the central Kalahari in response to vegetation greenness as assessed by satellite imagery
    (2016-01-22) Relton, Claire E
    Arid African savannas experience seasonal, variable rainfall, resulting in unpredictable patterns in vegetation distribution. Understanding the spatio-temporal variability in primary productivity and the resulting behavioural responses of native herbivores is essential for the analysis of the vulnerability of savanna ecosystems to climatic and human-induced threats. The Central Kalahari Game Reserve (CKGR), Botswana, is open to free-ranging wildlife to its south and west. The mostly homogeneous dune landscape is interspersed with valley and pan systems, which deviate considerably from dune regions in their soil and vegetation structures. I assessed the phenology of green vegetation across the pan-valley and dune habitats of the northern CKGR, using Normalized Difference Vegetation Index (NDVI) imagery, and related variations in greenness to the ecology of gemsbok (Oryx gazella), a herbivore species that is highly adapted to arid conditions. Eight female gemsbok were collared in the northern CKGR, and their patterns of habitat selection and responses to three greenness measures (NDVI, ΔNDVI and Relative Greenness) were assessed using logistic regression models. Gemsbok 12-hour displacement distances for each herd were compared seasonally to assess whether gemsbok in the northern CKGR differ in their movement strategies depending on the prevailing environmental conditions at that point in time and space. The northern CKGR experiences high inter-annual variability in NDVI greenness and phenology. Pan-valley and dune habitats did not have significantly different rates of green-up or green season durations, but dune habitats had higher NDVI levels. Patches with the highest greenness levels showed little spatial persistence from year to year. Gemsbok did not select for higher NDVI or ΔNDVI, but they selected for categories of relative greenness that were higher than the lowest relative greenness level. Gemsbok selected pan-valleys over dunes during the green season, but were not selective during the brown season, probably as a result of the loss of green grasses in pan-valley habitats during this period. Finally, gemsbok had no specific general trend in seasonal displacement distances. Gemsbok in the CKGR are likely to be opportunistic feeders, and herds probably made varying behavioural decisions based on their immediate environmental conditions.
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    Using remote sensing to explore the role of ambient temperature in determining gemsbok (Oryx gazella) usage of a heterogeneous landscape in the central Kalahari
    (2016-01-20) Tromp, Leon Rocher
    The central Kalahari is likely to become hotter and drier as a result of climate change in the region. These changes may result in behavioural changes in Gemsbok due to temperature induced stress, in spite of physiological and behavioural adaptations, and are likely to manifest in a preference for particular landscape patch classes. Recent Landsat 8 satellite imagery and classification analysis were used to map landscape patch classes in a heterogeneous landscape in the central Kalahari. The classification map of the research area identified 6 classes of landscape patches used by Gemsbok. Eight collared Gemsbok were tracked by satellite to monitor their movement in their respective home ranges over a period of 9 months. Gemsbok locations were plotted on to the classification map, and location frequency distributions were produced for each landscape patch class. Gemsbok home ranges were calculated using minimum convex polygon geometry, and the available patch class areas within each home range were analysed against the usage patterns of each animal. The analysis showed less preference for shade producing classes and more preference for open classes. Exploration of the role of temperature in landscape patch selection showed that temperature is a weak predictor of patch class, that critical temperature thresholds have not yet been reached, and that Gemsbok preference for pans is more likely related to seasonally available forage and reduced predation risk in a “landscape of fear” (Laundré, Hernández, & Altendorf, 2001).