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theses

Food is an essential for individual survival and reproduction, but intrinsically presents a variety of mechanical obstacles that must be met and nutritional requirements that must be overcome by the consumer. Mechanically, foods may be hard, tough, or stiff enough to inflict dental, damage on teeth, cranium, or facial form while chemically, it may be packed with toxins, nutrient deficiencies or in excess, which may harm the consumers' fitness. Therefore, feeding efficiency and challenges associated with foods provide a strong selective mechanism potentially influencing the evolution of foraging behavior and diet. The problems of accessing food and ensuring sufficient intake of energy and protein are likely to have a greater impact on juveniles than adults, as juveniles are smaller, less experienced and generally more inefficient foragers. Detailed studies testing the effects of these formative factors on juvenile feeding have yet to be conducted, however, and there is a poor understanding of how adult-juvenile foraging differs in nonhuman primates. The main debate on this issue centers on the development of juvenile foraging efficiency, particularly on the effects of body size, nutritional needs, and experience in driving the suggested adult-juvenile differences in feeding. In order to clarify understanding of adult-juvenile foraging differences, I collected data and compared the diet choice, metabolizable energy intake, the mechanical and nutritional properties of foods, and the interactive effects of these properties on food selectivity in the Tana River mangabeys, Cercocebus galeritus. This research addressed the following questions about the implications of mechanical and nutritional properties of foods on foraging. Compared to adult lactating females, how do juveniles differ in: (1) diet, particularly in food choice and energy intake?; (2) the influence of mechanical and nutritional properties on foraging decisions?; and, (3) food electivity as a result of interactive effects of the mechanical and nutritional properties of foods? I collected data on feeding behavior using focal animal sampling from two wild groups (Kitere & Mchelelo groups) in lower Tana River forest fragments, Kenya. I measured the fracture toughness and elastic modulus of the primary and fallbacks foods of the mangabeys using a portable FLS-1 food tester machine. Finally, I performed laboratory analyses to determine the nutritional properties of the foods. Overall, I found that dietary breath (BA) was wider in lactating females (BA = 0.13) than in juveniles (BA = 0.11) and was higher in Mchelelo group (0.22 & 0.17) than in the more anthropogenically impacted Kitere group (0.15 & 0.11) for both age classes, respectively. Juveniles’ mean metabolizable energy intake per metabolic body mass per minute was higher than in lactating females. Juveniles also ingested more available protein per metabolic body mass per minute than the lactating females. Lactating females ingested foods with significantly higher fracture toughness than juveniles, but elastic modulus values of the food did not differ between the two age classes. Moreover, fruit availability and the mechanical and nutritional properties of foods interacted to influence the diet selection across seasons of different fruit availability, but there were no age class differences. These findings supported my predictions that juveniles will ingest more protein and metabolizable energy per unit of metabolic body mass compared to lactating females potentially due to increased nutritional needs for growth. Additionally, differences in the mechanical properties of the foods ingested by juveniles and lactating females support the Need-To-Learn hypothesis that juveniles that require time to learn and acquire competence in feeding skills.

ETD_8683

Ph.D.

Includes bibliographical references

by Stanislaus Kivai

doi:10.7282/T3TT4V5X

ETD doctoral

The author owns the copyright to this work.