As an indicator of above ground net primary productivity, the Normalised Difference Vegetation Index (NDVI) has been identified as important tool in understanding the resource requirements and distribution patterns of large herbivores. The efficacy of NDVI as an ecological tool is however, strongly contingent upon the scale of the foraging hierarchy at which data are interpreted. In this study I investigated whether vegetation greenness, as represented by MODIS NDVI 250 m resolution imagery, is a driver of zebra (Equus quagga) foraging patterns at three spatial/temporal scales, namely location within sixteen day home ranges, sixteen day home range within seasonal home range and seasonal home range within total home range, during both wet and dry periods. I also investigated how tree canopy cover influences the ability of MODIS NDVI to see the greenness at which zebra respond. During the wet season, the zebra clearly demonstrated evidence of selecting for greenness and a tendency to avoid areas of high woody canopy at all three scales. Conversely, during the dry season the zebra showed no preference for greenness and no consistent preference for or against woody cover across the three scales. I also noted that despite a positive relationship between ΔNDVI and woody canopy cover, the relationship is not significant and suggests that in savanna ecosystems tree densities may not be high enough to affect overall MODIS NDVI readings. These results indicate that zebra foraging behaviour is complex and differs according to the scale of analysis, season, and even between individual zebra herds. The ability of MODIS NDVI to elucidate zebra movements is therefore limited to specific spatial and temporal scales and should be accompanied by an understanding of non-forage related factors.

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The effect of intracerebroventricular (ICV) injection of corticotrophin releasing hormone (CRH) and related compounds on appetite, behavior, and gastric motility in lines of chickens, one selected for low body weight (LWS) and the other high body weight (HWS), was determined. Nucleotide sequence and expression patterns of the CRHr2 receptor, involved in appetite regulation, were also determined. Some individuals of the LWS line are anorexics and many die simply from not eating while some individuals in the HWS line are compulsive eaters and exhibit obesity. CRH is a 41 residue peptide that initiates an organism's stress response and is a potent inhibitor of appetite. An ICV injection of CRH dose-dependently decreased feed intake in both lines but did not effect water intake. When CRH receptor antagonists were ICV injected an increase in feed intake in the LWS line but not in the HWS line was observed, however the appetite reducing effect of CRH was attenuated in the HWS line but not in the LWS line. The LWS line has higher concentration of corticosterone than does the HWS line. In both lines at all times treatment with CRH caused an increase in locomotion and no CRH-treated chicks from either line slept post injection. Chicks from the LWS line that were treated with CRH exhibited other anxiety related behaviors sooner than the HWS line. The LWS line showed a liner increase in crop emptying time as the dose of ICV CRH increased. The HWS line responded with a quadratic dose response to CRH treatment. Polymorphisms in the CRHr2 receptor were found in both lines in the same positions, thus we concluded these differences do not significantly contribute to body weight differences. However, differences detected in expression patterns between lines for the CRHr2 receptor may contribute to their different body weights. We conclude that differences in the CRH system, its concentrations and differential receptor action, of these two lines may be partly responsible for their altered body weight phenotype. / Ph. D.