Soutenance mémoire
CONCEPTION D’UN NOUVEL ESTIMATEUR DU DOMAINE VITAL
Introduction
Space-use dynamics and habitat selection by wild ungulates are shaped by the spatial and temporal heterogeneity of biotic and abiotic factors (Bailey et al. 1996; Fryxell et al. 2004). In addition, critical resources often are segregated spatially (e.g., the best places for feeding, drinking, resting, or lowering the predation risk might occur at great distances from each other), and such spatial segregation can vary across scales (Mueller et al. 2009). In this context animals are expected to adopt space-use and habitat selection strategies that allow them to minimize detrimental effects of the main limiting factors so as to reach, at different scales, suitable trade-offs between several constraints and needs that must be addressed simultaneously (Godvik et al. 2009; Massé & Côté 2009). We analyzed how space-use and habitat selection patterns of the West African savanna buffalo (Syncerus caffer brachyceros) are conditioned by the spatiotemporal segregation of limiting resources and by spatial segregation between neighboring herds at both annual and seasonal scales.
The African buffalo is a large gregarious grazer common in most sub-Saharan ecosystems. This species has a variable morphology, and 4 subspecies have been recognized. So far, most studies have focused on the Cape buffalo (S. c. caffer), which is found in eastern and southern Africa. The Cape buffalo is characterized by a large body mass (400-800 kg) and herd sizes averaging 350 individuals. Several authors (Halley et al. 2002; Prins 1996; Ryan et al. 2006) have suggested that Cape buffalo herds might use exclusive home ranges, and Korte (2008a) suggested similar spatial arrangements for the forest-dwelling buffalo (S. c. nanus). By contrast, the ecology of the West African savanna buffalo remains poorly known. To date, knowledge of this subspecies comes from sporadic aerial surveys, trophy records, and a few pioneer publications (Boy 1958; East 1998; Stark 1986). The West African savannah buffalo differs from the Cape buffalo by having a smaller body mass (350-450 kg) and smaller herd sizes (40-50 individuals—Boy 1958; Cornélis 2000). The total population covers 13 West African countries and has been estimated to comprise 20,000-27,000 individuals (East 1998; Estes 1991). Buffaloes are strongly water-dependent and need to drink daily (Sinclair 1977). In semiarid areas water availability often is restricted to a few permanent river segments during the dry season, and forage quality is low. In these conditions buffaloes face a tradeoff between nutritional and water requirements (Redfern et al. 2003), and were shown on some occasions to perform relatively large interseasonal movements (Funston et al. 1994; Halley et al. 2002). In West Africa perennial grasses are a key foraging resource for grazers Déterminants écologiques de l’utilisation de l’espace et du déplacement (Breman & De Ridder 1991; Stark 1986), as they generally present a higher feeding value (biomass, palatability, and nutrient content) than annual grasses. In addition, the energy stored in the root system of perennials allows a longer period of vegetative activity. In our study area perennials occur in high proportions mainly in remote areas where surface water is available only during the wet season. The buffalo herds living in our study area therefore were expected to face particularly severe conditions due to a spatiotemporal segregation in the availability of water and perennial grasses.
We investigated at both large (interseasonal) and small (intraseasonal) spatiotemporal scales how breeding herds use space, in relation to surface water locations and rainfall timing, and the extent to which they show marked preferences in habitat use and share space with neighboring herds. We monitored the movements of 7 herds for several months, including the dry-wet season transition, which was expected to generate the largest change in space-use patterns. We expected space-use patterns to be constrained strongly by access to surface water in the dry season and by spatial segregation between neighboring breeding herds all year. At the dry-wet season transition buffalo were expected to shift to areas encompassing both higher quantities and qualities of forage, as measured respectively by the primary production and the proportion of perennials. At the intraseasonal scale buffalo also were expected to display a preference for the areas characterized by high primary productivity and dominated by perennials.
Material and Methods
Study area
The field study was conducted from March 2007 to November 2008 in the « W » Regional Park (WRP), a transboundary (Benin, Burkina Faso, and Niger) Biosphere Reserve located in the upper Niger basin (1.98–3.08°E, 11.37–12.58°N). The WRP covers 10,339 km2 and supports a population of about 3,000 buffaloes. Despite occurring at a relatively low density in comparison with buffaloes in other ecosystems, buffalo are the most abundant ungulate of the WRP (Bouché et al. 2003; Hibert et al. 2004 ). The area exhibits a climatic gradient along a north-south axis from Sahelian to Sudanian climatic zones, with a mean annual rainfall ranging from 685 mm (north) to 850 mm (south). The wet season extends from April-May to September-October. Topographically, the WRP is a peneplain drained by 5 main rivers (Figure 20 p129). After the onset of the dry season the eastern rivers generally dry out completely, and the Tapoa River shrinks to a permanent portion 4 km in length, located immediately upstream of a catchment dam. In contrast, Mekrou River dries out only partially, turning into an irregular chain of ponds. In the wet season a multitude of small depressions retain water throughout the WRP, but most of them dry out rapidly, except for a few (<5) that are fed partially by natural springs or supplied with water pumps (Hibert 2007).
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Table des matières
A.1. Avant propos
A.2. Résumé
A.3. Summary
A.5. Remerciements
A.6. Liste des manuscrits
CHAPITRE 1. INTRODUCTION GENERALE
A. Contexte et enjeux
B. Problématique et questions de recherche
C. Structure du document
D. Etat de l’art
D.1. La démarche « patrons-processus » en écologie
D.2. Les questions d’échelles en écologie
La théorie de la hiérarchie
Des échelles et de leur identification
D.3. Le domaine vital : un patron spatial clé en écologie animale
Un sujet d’étude en soi
Les estimateurs déterministes et statistiques du domaine vital
Les estimateurs mécanistes Vers une intégration des approches
D.4. Le concept de la sélection de l’habitat
Cadre théorique
Le concept d’habitat
La sélection de l’habitat : protocoles, procédures analytiques et limites
D.5. L’écologie du déplacement : un cadre conceptuel innovant
D.6. Revue des outils et protocoles applicables à l’écologie du déplacement.
Echantillonner le déplacement
Evaluer l’état interne
Caractériser les facteurs externes
CHAPITRE 2. MATERIEL ET METHODES
A. La zone d’étude
A.1. Milieu physique
A.2. Végétation
A.3. Faune
B. Le buffle africain
B.1. Organisation sociale
B.2. Alimentation
B.3. Domaine vital
B.4. Reproduction
C. Le dispositif experimental
C.1. Tracking GPS
Matériel
Dispositif d’échantillonnage
C.2. Variables environnementales
C.3. Echantillonnages fécaux
CHAPITRE 3. CONCEPTION D’UN NOUVEL ESTIMATEUR DU DOMAINE VITAL
A. Abstract
B. Introduction
C. Methods
D. Results
E. Discussion
F. Acknowledgments
CHAPITRE 4. ANALYSE COMPARATIVE QUANTATIVE D’ESTIMATEURS DU DOMAINE VITAL
A. Abstract
B. Introduction
B.1. Criteria for selecting home range metrics
B.2. Statistical comparison of home range metrics
B.3. An AUC-based comparison of home range metrics
C. Results
D. Discussion
E. Acknowledgements
CHAPITRE 5. DETERMINANTS ECOLOGIQUES DE L’UTILISATION DE L’ESPACE ET DU DEPLACEMENT
A. Abstract
B. Introduction
C. Material and Methods
C.1. Study area
C.2. Sampling designC.3. Herds movements and activity monitoring
C.4. Home range and space sharing computation
C.5. Habitat selection analyses
C.6. Statistical analyses
D. Results
D.1. Buffalo concentrations and herd size
D.2. Large scale space use dynamics
D.3. Small scale habitat preferences
D.4. Space sharing and spatial fidelity
E. Discussion
F. Acknowledgments
CHAPITRE 6. COMPORTEMENT SPATIAL ET BIORYTHMES
A. Introduction
B. Material and Methods
B.1. Study area and buffalo population
B.2. Data recording
Movement and sensor data
Environmental covariates
B.3. Data analyses
Seasonal and sub-annual space use patterns
Biorhythm analyses
Statistical analyses
C. RESULTS
C.1. Space use and selection patterns
Herd 1
Herd 2
Herd 3
Herd 5
Herd 7
C.2. Biorhythms
Movement speed
Activity patterns
Diurnality index
Degree of functional coupling
D. Discussion
D.1. Space use and habitat selection patterns
D.2. Biorhythms
D.3. Conclusion and future directions
E. Figures
CHAPITRE 7. STRESS, REGIME ALIMENTAIRE ET CHARGE PARASITAIRE
A. Abstract
B. Introduction
C. Material and Methods
C.1. Study area and African buffalo population
C.2. Collection and processing of faeces
C.3. Faecal glucocorticoid assay
C.4. Diet quality analysis using NIRS
C.5. Coprological investigation for parasites
C.6. Statistical analysis
Indices of diet quality
Indices of parasitism
Description of variation between herds and seasons
Quantification of the variation between herds and seasons
Relationship between FC levels, parasitism and diet quality indices
D. Results
D.1. Faecal cortisol levels
D.2. Diet quality
D.3. Parasitological investigations
D.4. Influence of diet quality on faecal cortisol levels
D.5. Influence of parasite infection on faecal cortisol levels
E. Discussion
E.1. Glucocorticoid patterns
E.2. Faecal cortisol levels and parasitism
E.3. Faecal cortisol and diet quality
F. Conclusions and future directions
G. Acknowledgments
CHAPITRE 8. SYNTHESE GENERALE
A. Résumé des principaux résultats
Développements méthodologiques
Ecologie du buffle de savane Ouest-africain
B. Limites de l’étude
Echantillonnage
Sélection de l’habitat : les limites d’une approche dynamique
Suivis fécaux
C. Ecologie du déplacement du buffle au PRW
Patrons et processus de déplacement
Ressources alimentaires et état interne
Compétition intra-spécifique
D. Implications pour la conservation et la gestion du buffle de savane Ouest-Africain
E. Perspectives
Identification de patrons de déplacement récursifs Du comportement de déplacement au budget d’activité
CHAPITRE 9. BIBLIOGRAPHIE
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