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A social group of 37 mandrills, with composition resembling a wild group, maintained in a 5.3 ha enclosure of natural relict gallery forest at CIRMF, Gabon was studied over 29 months. The 14 wild-caught founders (7 adult females, 2 adult and 5 subadult males) were the subjects of detailed behavioural study (15 months, 1200+ hours observation). Mandrills were captured at least annually to obtain blood samples, data on body weight, dental and reproductive status, and testicular volume. Breeding was seasonal, with a 4-month mating season in which 92% of oestrous periods occurred. Oestrus synchrony was evident, with up to 5 females maximally swollen on any one day. Most (92%) copulations occurred at maximum swelling, with ejaculation in a single mount. 'Mate-guarding' of pen-ovulatory females by the alpha male involved sustained proximity to her and 'warning grunts' to other males. No herding behaviour was observed. Spatial, grooming, and agonistic relationships were examined in detail. During anoestrus, males were rarely near females; three males were never recorded allogrooming. The alpha male spent significantly more time close to anoestrous females, grooming with them significantly more than the other males. Females spent time near each other, groomed with their offspring, and gave three-quarters of their grooming to and received nearly all grooming from founder females. During oestrus, male-female proximity increased, females spent more time grooming, groomed with fewer age-sex classes, groomed mostly with male founders, and received more grooming from males. Stable, linear dominance hierarchies existed within each sex. Various aspects of mandrill biology - colouration, scent-marking, vocalisations - were interpreted as adaptations to ecological constraints of living semi-terrestrially in tropical forest. Results were used to assess models of single- and multi-male social organisation and male mating strategies. It was suggested that mandrills form one-male units, different from those of hamadryas and gelada baboons. Instead similarities with an Asian ecological analogue of the mandrill, the pig-tailed macaque, were emphasised.

Le régime alimentaire est un élément clé de l’écologie des espèces et dépend à la fois des besoins nutritionnels des individus et des ressources alimentaires disponibles. Ainsi, les stratégies alimentaires peuvent varier en fonction de l’âge, du sexe ou de l’état physiologique des individus, mais également de paramètres environnementaux et, en particulier, de la saisonnalité. Reconstruire le régime alimentaire d’espèces cryptiques ou difficiles à observer en milieu naturel nécessite l’emploi de marqueurs capables de détecter les variations du régime alimentaire sur le court terme. L’analyse des patrons de micro-usures dentaires et des ratios d’isotopes stables du carbone et de l’azote constitue une approche pertinente pour distinguer le régime alimentaire entre différentes espèces ou entre populations. Dans le cadre de cette thèse, nous avons évalué le pouvoir prédictif de ces deux types de marqueurs sur les variations saisonnières et interindividuelles du régime alimentaire dans une population naturelle de mandrills (Mandrillus sphinx) sur laquelle des données comportementales étaient disponibles. Conformément aux comportements alimentaires observés, les patrons de micro-usures dentaires et les signatures isotopiques varient en fonction de la saison, de l’âge et du sexe des individus. L’ensemble de nos résultats nous indique que la diversité importante d’aliments consommés à faible fréquence par les mandrills ne peut être détectée par les marqueurs analysés qui semblent être, en revanche, pertinents pour identifier des changements significatifs de consommation d’aliments majoritaires tels que les fruits et les feuilles. Enfin, les signatures isotopiques varient en fonction du cycle reproducteur des femelles et de leur rang de dominance, nous indiquant que l’utilisation de tels marqueurs peut permettre la mise en évidence d’aspects de la physiologie des individus non reportés par des observations comportementales. Les résultats présentés dans cette thèse apportent des données de référence essentielles pour la reconstruction du régime alimentaire d’espèces éteintes partageant des traits communs avec le mandrill, telles que des primates généralistes de forêts tropicales. / Diet is a critical factor of species’ ecology and depends on both individuals’ nutritional needs and availability of their food resources. As such, feeding strategies may vary with age, sex or physiological condition of the individuals but also depend on environmental factors and, in particular, seasonality. In cryptic species and those that are difficult to observe in their natural habitat, diet reconstruction requires the use of proxies with the ability to detect dietary variations over the short term. Analyses of dental microwear patterns along with carbon and nitrogen stable isotopes constitute a relevant approach to discriminate between diets of different species or populations. In the framework of this thesis, we assessed the predictive power of these two proxies on seasonal and inter-individual variations of diet in a natural population of mandrills (Mandrillus sphinx) for which behavioural data was available. According to the feeding behaviours observed, dental microwear patterns and isotopic signatures vary depending on the season as well as individual’s age and sex. Taken together our results indicate that the large diversity of rarely consumed food items cannot be detected by the proxies analysed, which are however, relevant to identify significant changes in the consumption of major foods such as fruits and leaves. Finally, isotopic signatures vary across females’ reproductive statuses and dominance ranks, indicating that the use of those proxies may allow the highlighting of some aspects of individuals’ physiology not detected by behavioural observations. The results presented in this thesis provide a baseline data essential for dietary reconstruction of extinct species sharing similar traits with mandrills, such as generalist primates from tropical forests.