In group living species animals commonly compete for limited resources such as food (Darwin 1859). Winning competition for food may be beneficial for an individuals survival or reproductive success (Williams 1966; Clutton-Brock 1988; Metcalfe et al 1995) but conflict with group members may be costly as it typically involves aggression (Huntingford&Turner 1987, Mesterton-Gibbons&Adams 1998). Asymmetries between individuals are predicted to determine the outcome of competition (Maynard-Smith&Parker 1976), and individuals are expected to steal food when the benefit to them is greatest (Barnard 1984; Trivers 1972). I therefore investigate what determines the outcome of competition for food between group members, and what factors affect whether group members try to steal food in the cooperatively breeding meerkat (Suricatta suricatta). Meerkats competed for food items infrequently and the owner of a food item typically won competition, but dominant individuals and breeding females were more likely to win competition than other group members. This provides support for models of conflict over resources in group living species which predict that ownership may determine the outcome of competition, thereby avoiding frequent costly conflict (Maynard-Smith 1982). Furthermore, where large asymmetries exist between contestants in dominance status or the value of a resource, these may determine the outcome of competition (Maynard-Smith&Parker 1976; Grafen 1987). Meerkats varied in how frequently they tried to steal food depending upon the costs and benefits of competition. Dominant individuals competed for food more frequently which is likely to reflect reduced costs of competition as subordinate individuals may avoid conflict with them (Packer&Pusey 1985). Females competed for food more frequently than males and more frequently during breeding, reflecting the higher costs of reproduction to females compared to males (Williams 1966; Trivers 1972). Meerkats compete more frequently for food when food availability is low, which indicates that food items may be more valuable when they are rare. Meerkats in smaller groups competed more frequently. In cooperatively breeding species group members undertake a large number of costly helping behaviours. Individuals in small groups each contribute more effort to helping than individuals in large groups and suffer higher costs which may increase the benefit of food to them (Clutton-Brock et al 1998a; Clutton-Brock et al 2001a). Competition for the opportunity to breed in cooperatively breeding meerkats has resulted in despotic dominance hierarchies where a dominant female monopolises breeding and reproductively suppresses subordinates (Clutton-Brock et al 2001b). Dominant females stole more food than any other group members. This is likely to be a consequence of the high costs of reproduction for the dominant breeding female in species with high reproductive skew (Creel&Creel 1991; Clutton-Brock et al 2001b). Furthermore, dominant females were more aggressive and more successful in competition for food with their reproductive competitors. Dominant females may therefore use competition for food as a means of asserting dominance over their reproductive competitors which could contribute to reproductive suppression (Creel et al 1992; Williams 2004; Kutsukake&Clutton-Brock 2006b; Young et al 2006). / Dissertation (MSc)--University of Pretoria, 2011. / Zoology and Entomology / unrestricted

L’objet de ce travail de thèse est le regroupement des essences bois du bassin du Congo en quatre groupes en fonction de la similitude de leurs propriétés mécaniques essentielles. Le module d’élasticité (MOE), propriété indicatrice, est estimé par une méthode non destructive : l’essai vibratoire. Pour chaque classe, le fractile à 5% d’exclusion supérieur d’une propriété mécanique est calculé à partir d’une théorie clairement exposée. Le bassin du Congo est un patrimoine en danger à cause des pressions anthropiques au premier rang desquelles figure la coupe hyper sélective des essences bois. Le résultat de ce regroupement permet de proposer comme substitut aux essences menacées d’extinction des essences aux propriétés mécaniques similaires plus disponibles en terme de ressources sur pied. D’où la contribution à la gestion durable et au maintien de la biodiversité du bassin du Congo. On montre que le MOE vibratoire est quasi-invariant avec la teneur en eau et qu’il est bien corrélé au MOE statique, à la masse volumique et à la contrainte à la rupture. C’est donc un bon prédicteur du module de rupture (MOR) à 12% du taux d’humidité du bois vert. Ceci valide l’organisation en groupe d’essences réalisée dans ce travail. Les valeurs caractéristiques des propriétés mesurées sont calculées pour chaque classe. Parce que l’Eurocode 5 exige que les bois utilisés en structure soient classés, nous proposons, in fine, un système de classement en structure des bois du bassin du Congo voué à une meilleure utilisation des forêts pour la conservation des écosystèmes forestiers et la satisfaction des besoins fondamentaux de l’homme. / This Ph.D. work deals with a non-destructive experimental approach organizing the species of the Congo basin in four groups according to the likeness of their main mechanical properties, and to guarantee for each group the 5th percentile characteristic value of mechanical properties such as the modulus of elasticity (MOE). For the sustainable management of forest and conservation of exotic biodiversity of the Congo basin, it is necessary to promote the exploitation of less-consumed species with equivalent mechanical characteristics. The aim of the present work is to propose a scheme for grouping species with similar values of modulus of elasticity (MOE) obtained through vibratory method. Only small clear specimens are tested. The assignment of a given specie to one of the four groups takes place in return for a homogeneity test of comparison of the random variables of species to the random variable of the group. Results of the present grading show that some species can be interchangeably consumed in the construction industry and that the procedure must include more species of the Congo basin. This property grouping will facilitate substitution of underutilized species for ones that are being more exploited. Thus, wood designers and constructors might have a wide variety of choices in their decision-making while promoting less-consumed species and reducing the demand of traditionally most wanted extinguishable species. The MOE obtained by intrinsic vibration of wood versus is not influenced by moisture content. So, the non destructive method bases on longitudinal vibrations can be used in industrial production of timber to certify the modulus of rupture (MOR) at 12% moisture content of green wood by direct correlation. Finally, we propose a grading system of tropical wood.